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Synthroid (Levothyroxine) & Weight Gain: An Uncommon Reaction

Synthroid (Levothyroxine) is a medication commonly prescribed for the treatment of hypothyroidism, and is also a popular intervention for goiters, nodular thyroid disease, and thyroid cancer.  Administration of synthroid reverses neurophysiological irregularities associated with insufficient thyroxine (T4) and reduces concentrations of TSH (thyroid-stimulating hormone).  Within several months of synthroid administration, many individuals report improvements in mood, energy, and overall well-being.

Although synthroid is a synthetically-engineered form of thyroxine called “levothyroxine,” and isn’t bioidentical to endogenously secreted thyroxine (via properly functioning thyroid glands), it is similar enough to improve hypothyroidism biomarkers and symptoms.  Assuming the dosage of synthroid is properly calibrated for the specific user, severe side effects and/or adverse reactions are unlikely.  Most people are able to tolerate synthroid over a long-term (many years) without complaints of unwanted side effects.

Despite the favorable tolerability of synthroid for most users, a subset of users report significant unwanted synthroid side effects, one of which is often weight gain.  It is unclear as to how synthroid may cause weight gain as most literature suggests that it is “weight neutral” or unlikely to affect body weight.  However, there is some evidence to suggest that older adults (ages 45 and up) may gain weight as a result of synthroid treatment.

Synthroid (Levothyroxine) and Weight Gain

Firstly, it is important note that most medical literature suggests that synthroid does NOT cause significant weight gain.  However, assuming you haven’t made any profound changes in eating habits, activity/exercise level, etc. while taking synthroid, yet you’ve packed on a noticeable amount of poundage – it’s probably safe to assume that it was triggered by the drug.  Just because the majority of synthroid users are unlikely to gain weight, does not mean that synthroid-induced weight gain should be dismissed as a medical impossibility.

There’s never a one-size-fits-all response to medications – responses (and especially synthroid side effects) are subject to interindividual variation.  While most people may not gain weight from synthroid, you may happen to be the outlier who ends up packing on the poundage; possibly to a significant extent.  It may be frustrating to inquire about synthroid as the culprit for your weight gain to a medical professional, especially if you are told “synthroid does not cause weight gain.”

This may lead you assess any recent changes in: dietary intake, exercise level, sleep, stress, etc. – only to realize that nothing much has changed.  At this point, you may want to talk to your doctor about going without synthroid and/or switching to another medication to see if your weight normalizes.  That said, you should keep in mind that temporary fluctuations in body weight may be common over the first few weeks or months of synthroid treatment; these may subside with continued synthroid administration.

How Synthroid May Cause Weight Gain (Possibilities)

There are numerous possible ways in which synthroid administration could cause weight gain in a subset of users.  Understand that there may be interindividual variation in the causative factors responsible for the weight gain.  Some individuals may gain weight as a result of the fact that their appetite increases while taking synthroid, yet another person may realize that synthroid causes bloating and/or changes in gut bacteria that lead to weight gain.

  • Appetite increase: Though some individuals find synthroid beneficial for reducing appetite, others notice a significant increase in appetite during synthroid treatment. Any increase in appetite, regardless of whether small or large, will increase the likelihood that you’ll consume more food (and calories throughout the day).  The more food that you consume throughout the day, the more likely you’ll be to gain weight.
  • Bloating: A side effect that synthroid users report is stomach bloating characterized by heightened build-up of fluid and/or gas. If you feel bloated while taking synthroid, you’re certainly not alone.  Some people report such severe bloating, that they appear as if they’re pregnant.  It may be necessary to consider that the extra weight retained as a result of bloating may be perceived as minor weight gain.
  • Constipation: In addition to bloating, some individuals note that synthroid induces constipation. If you find it difficult to pass a bowel movement, some of the increased weight that you notice may be a result of your constipation.  It may be helpful to intervene with increased dietary fiber, hydration, and/or laxative agents.  Keep in mind that constipation is unlikely to cause a significant amount of weight gain, but may contribute slightly to your overall weight increase if you experience it.
  • Food cravings: Although fairly rare, some users report hunger pains and/or substantial food cravings while taking synthroid. You may find yourself craving unhealthy foods such as: candies, cookies, and various sugary treats.  Assuming you are unable to resist these cravings, you’re probably going to gain some weight.  To minimize your chances of falling victim to food cravings, you may want to avoid purchasing any foods that reinforce these cravings during synthroid treatment.
  • Gut bacteria: Pharmaceutical medications, especially synthetic ones like synthroid, may be altering your gut microbiome. In other words, regular administration of synthetic thyroxine (levothyroxine) may alter the densities of particular gut bacterium.  As a result of changes in gut bacteria associated with synthroid, users may gain weight without any dietary or exercise changes solely resulting from bacteria in the gut.
  • Low energy: Not everyone feels energetic and spry after taking synthroid. Some individuals report feeling lower energy after taking synthroid than prior to treatment.  If you notice that you become increasingly fatigued and/or lethargic throughout treatment, chances are that you’ll gain some weight.  Fatigue makes it difficult to remain physically active, engage in regular exercise (to burn calories and keep metabolism high), and also difficult to make healthy decisions regarding foods to eat.
  • Neurotransmission: Regular administration of synthroid may decrease concentrations of dopamine. Precursors such as tyrosine appear to decrease in the brain of rodents regularly administered synthroid.  It is plausible to consider that humans who’ve taken synthroid for a long-term may end up with low dopamine (at least in certain regions of the brain).  Reductions in dopamine could lead to poorer appetite control, feeling less satiated after eating, etc. – possibly contributing to weight gain.
  • Sleep disturbances: It is understood that a quality night’s sleep is beneficial for maintaining a healthy body weight. Adequate deep sleep keeps the metabolism within a healthy range and allows the body to produce hormones to prevent weight gain.  Lack of sleep increases ghrelin (the hunger hormone) and may disrupt other metabolic processes, ultimately leading to weight gain.  Since synthroid administration may cause insomnia and sleep disturbances in some users, its interference with a good night’s sleep may indirectly contribute to weight gain.  (Source: http://www.ncbi.nlm.nih.gov/pubmed/18564298).
  • Synthetic reaction: The fact that synthroid is a synthetic, rather than bioidentical hormone is problematic for many users. The chemical structure of synthroid differs from endogenously produced thyroxine (T4), and as a result, it may provoke abnormal and unpredictable neurophysiological reactions in users.  Weight gain may be one of many possible implications associated with using a synthetically-manufactured hormone, as opposed to one that is endogenously secreted (or even bioidentical).

Variables that may influence weight gain from Synthroid (Levothyroxine)

Whenever contemplating the weight you’ve gained from synthroid, it may be helpful to consider influential variables.  Examples of such variables to consider that may affect weight gain include: synthroid dosage, duration of administration, other medications or drugs, and your lifestyle.  Some users may find that they were gaining weight from an improper synthroid dosage, while others may realize that weight gain could be caused by other pharmaceutical medications.

  1. Synthroid dosage

The dosage of synthroid that you’re taking may affect whether you’re likely to gain weight.  Individuals taking extremely high dosages are more likely to lose weight than gain weight.  High dosages of synthroid are thought to increase basal metabolic rate (BMR) and the number of calories burned at rest.

On the other hand, those taking low dosages of synthroid may end up gaining weight as a result of inadequately treated hypothyroidism.  At extremely low dosages, you may not attain enough synthroid to counteract the metabolic slowing that occurs with hypothyroidism.  It may take your doctor awhile to find the optimal dosage to get your TSH levels within a normative range.

Synthroid dosing is known to have an NTI (narrow therapeutic index).  In some cases, even high-dose users may end up gaining some weight – assuming their neurophysiology reacts unusually to the synthroid.  A properly calibrated dosage by a medical professional (e.g. endocrinologist) should help reduce likelihood of weight gain (or loss) while taking synthroid.

  1. Duration of administration

The duration over which you’ve taken synthroid (levothyroxine) may affect how likely you are to gain weight.  It is possible that some users may gain weight over a short-term (e.g. less than 3 months of treatment), while others may notice some weight gain over a longer-term (e.g. 3+ months or years).  The shorter the duration over which you’ve taken synthroid, the more likely you are to experience transient weight fluctuations.

Short-term: Those that have taken synthroid for just a short-term may be undergoing a transient physiological adjustment in which some weight is gained.  However, with continued treatment (e.g. over the course of months and/or years), body weight is likely to normalize and weight that was initially gained may be lost.  If you’ve gained weight over the short-term (e.g. less than 3 months), don’t rule out the fact that you may eventually lose this weight.

Long-term: It is possible to consider that individuals who didn’t gain weight over a short-term, may end up gaining some weight over the long-term.  If you lost weight over the short-term with synthroid, it could’ve been a result of a neurophysiological overreaction.  Additionally, short-term weight loss may be a result of too high of a synthroid dosage.  Once the neurophysiology adjusts to synthroid (over a long-term) and/or an abnormally high dose is reduced, users may gain back some of the excess weight that was initially lost.

  1. Other medications

When taking synthroid, it is necessary to consider that other medications and/or dietary supplements may be affecting your weight.  Certain medications and/or supplements may decrease the absorption of synthroid (especially if you take them within 4 hours of synthroid).  This may lead you to gain weight while taking synthroid due to the fact that you’ve reverted back to a state of (subclinical) hypothyroidism as a result of poorer synthroid absorption.

It is also necessary to reflect upon the fact that other medications may be the sole cause for your weight gain.  Although you may suspect that your weight gain is caused by the synthroid, other medications and/or dietary supplements should be ruled out as potential causes.  If you have any questions as to whether another drug (or supplement) is leading to weight gain – talk to a medical professional.

  1. Individual factors

It is necessary to consider that individual factor such as: dietary intake, exercise/activity level, sleep (quality/quantity), and stress – can each affect body weight.  A person’s age and genetics may also affect how they respond to the synthroid and whether they gain weight.  If you’ve gained weight while taking synthroid, you may need to assess whether: diet, exercise, sleep, and/or stress changed throughout your treatment.

  • Age: Research indicates that adults over 45 year of age are most likely to gain weight with synthroid treatment. Studies suggest that the average amount of weight gained among older adults is 4.85 lbs (2.2 kg).  While this isn’t necessarily a large amount of weight gain, it may be noticeable in certain users.  If you are a younger individual (under the age of 45), significant weight change is considered unlikely.
  • Dietary intake: If your diet changed significantly after starting synthroid and you’ve gained weight, it is impossible to chalk your weight gain up to the synthroid. On the other hand, if your diet has stayed nearly the exact same during treatment (as it was pretreatment), diet can be ruled out as an influential factor.  That said, you should make a conscientious effort to eat healthy foods to minimize likelihood of weight gain.
  • Exercise: Some individuals end up gaining weight while taking synthroid because they stop exercising and/or become physically less active. If you stop working out at some point during synthroid treatment and gain weight, it’s most likely not a result of the synthroid.  Getting plenty of exercise and staying physically active during synthroid treatment is often helpful for weight management.
  • Genetics: It is possible that individual genetics may predict responses to synthroid, as well as weight changes. Certain individuals experience severe side effects while taking synthroid, yet others don’t experience any side effects – this may be a result of genetics.  Your genes may determine how you react to synthroid in terms of weight change.
  • Sleep: Although synthroid can cause sleep disturbances (which could indirectly lead to weight gain), poor sleep hygiene may also cause weight gain. If you don’t get enough sleep as a result of your personal decision to stay up (e.g. to hang out with friends, use the computer, etc.) – realize that you may gain weight.  Managing sleep hygiene is important to ensure that you won’t gain weight while taking synthroid.
  • Stress: Your stress level experienced while taking synthroid could affect whether you end up gaining weight. Those who experience a sudden increase in stress may find it difficult to get proper sleep and/or may end up gaining weight as a result of stress-induced hormonal changes.  You may want to avoid blaming synthroid for weight gain if you’ve recently experienced high stress.

Synthroid (Levothyroxine) & Weight Gain (The Research)

There is limited scientific evidence to support weight gain associated with synthroid.  Few studies have taken the time to investigate whether synthroid (levothyroxine) administration could cause weight changes, especially when administered over a long-term.  There’s only modest evidence from a 2010 study suggesting that older adults (ages 45+) may gain a little bit of weight from synthroid treatment.

2010: The effects of levothyroxine substitution on body composition and body mass after total thyroidectomy for benign nodular goiter.

Research by Ozdemir et al. (2010) documented the effects of levothyroxine (synthroid) on body mass index and composition among individuals subject to a total thyroidectomy (removal of the thyroid gland via surgery).  Their motive for investigating how thyroxine effects body mass and composition stemmed from the fact that many thyroidectomy patients complain of weight changes following surgery.

Researchers measured BMI and composition of all patients prior to the thyroidectomy, and then again 3-weeks post-surgery.  After the thyroidectomy, all patients received levothyroxine at dosages of 50 to 200 mcg per day.  All dosages were adjusted with the intent of optimizing TSH, FT4, and FT3 levels.

Upon comparison of the pre-thyroidectomy measures in body weight, there appeared to be no significant change in weight among the 22 participants that completed the study.  However, upon closer analysis, older adults (ages 45-64) experienced slight weight gain as a result of levothyroxine.  Older adults gained an average of 4.85 lbs (2.2 kg), whereas younger adults (under 45 years of age) didn’t experience any weight changes.

Although this is a small-scale study and it is unclear as to whether results can be generalized to other older adults taking levothyroxine (or non-thyroidectomy patients), and/or whether weight loss would be more significant over a longer duration – the study provides some evidence to suggest that levothyroxine may cause weight gain.  Follow-up research is necessary to confirm preliminary findings in this study.  That said, older adults (particularly thyroidectomy patients), may gain weight during levothyroxine treatment within 3-weeks of starting treatment.

  • Source: http://www.ncbi.nlm.nih.gov/pubmed/21077724

How much weight will you gain from synthroid (levothyroxine)?

Assuming you gain weight from taking synthroid (levothyroxine), it is unlikely to be an overwhelming amount.  Even if you do gain quite a bit of weight when starting treatment, keep in mind that it may take your neurophysiology awhile to accommodate and/or adapt to the drug.  Once your body adapts to the presence of synthroid, you may end up losing some of the weight that you initially gained.

However, others may notice that they actually lose weight when starting treatment, but over a long-term, they end up gaining a significant amount of weight.  Although it’s difficult to prove that the synthroid was the cause of weight gain over a long-term, it should be considered as a possibility.  User reports have documented weight increases throughout treatment ranging from 5 lbs to 30 lbs, however, it is unclear as to whether other factors played a role in the weight gain.

Does everyone gain weight from taking synthroid (levothyroxine)?

No. In fact, many people report weight loss from synthroid treatment.  Individuals with severe hypothyroidism often gain weight due to slowing of BMR (associated with hypothyroidism).  When basal metabolic rate is sped up to a normal range after treatment with synthroid, most users end up losing some weight.

Additionally, many individuals taking synthroid notice zero change in weight or remain “weight neutral” throughout treatment.  Don’t be surprised if your weight stays relatively similar throughout treatment as it was pre-treatment.  Only a small subset of synthroid users are thought to gain weight, and in these cases, it is unclear as to whether the weight gain was caused directly by the medication.

Have you experienced weight gain from synthroid (levothyroxine)?

If you’ve taken synthroid, leave a comment mentioning whether you’ve gained weight as a result of treatment.  To help others get a better understanding of your situation, mention: the amount of weight you gained, your synthroid dosage, as well as how long you’ve been taking it.  Do you believe that the weight you’ve gained is a solely from the synthroid or from a combination of factors (including synthroid)?

For those that experienced short-term weight gain (e.g. gain in less than 3 months), did it stabilize with long-term synthroid treatment?  Is there any way you can be sure that the weight gain was from synthroid?  Did you rule out other potential causative factors such as changes in: sleep, diet, other medications, exercise, etc. – to know that the weight gain was from synthroid?

If you have any particular theories as to how synthroid may cause weight gain, include an explanation in your comment.  Additionally, if you have any tips for regulating body weight while taking synthroid that you’ve found effective, be sure to mention them.  Although most users will remain weight neutral while taking synthroid, you may be one of the (unlucky) few who ends up gaining weight.

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48 thoughts on “Synthroid (Levothyroxine) & Weight Gain: An Uncommon Reaction”

  1. I had a total thyroidectomy 8 years ago and have been on Synthroid ever since. I went from 162 to 182 and lost all my zip. I always had lots of energy and now I want to do things but am too tired to do them. Four months ago I changed the way I was taking Synthroid.

    Instead of taking it when I woke up around 7 am I now take it during the night between 2:30 and 4 as that’s when I seem to wake up and roll over each night. My TSH went from 1.22 to .06.

    My endocrinologist changed my 112 to 100 and will see him next month (in the mean time I went to my family doctor and my TSH was .35. Going up but still low). Curious to see what it will be in another month and what my endocrinologist will do.

    • I have been on Thyroid medication for around 10 years now. Prior to going on replacement, my measured TSH was > 250. That zero is not a typo. At the time, I weighed 180 pounds (6’0 male in 20’s back then) and could trivially run 2 miles under 12 minutes.

      I also lifted regularly…no super athlete but clearly in good shape. At the time, I ate 2800 calories per day, both before and after treatment. Maintaining same diet and exercise, I gained 50 pounds in six months on levothyroxine.

      Normally, this would be a huge red flag in medicine but apparently it’s “in the heads” of a large subset of thyroid patients, never mind the implication that I suddenly lost track of 1000 calories per day for six months after maintaining weight for years. SURELY, that’s the explanation.

      Anyway, after a long struggle, a few years ago I went to a place to measure RMR and got a value of 2256 calories/day. I then began tracking this again, consistently eating 2200-2400 calories per day and exercising 3 times per week (no longer in the great shape I was above).

      I lost no weight after two months. According to what we’re led to believe… that’s not mathematically sound. But I did this meticulously, because it was important piece of evidence for my own reasoning and sanity. I then switched to desiccated thyroid and have lost around 15 pounds. Useful, but far from the 50 I’d gained. I remain there today.

      The switch was a result of desperation, a result of reading a large amount of the literature myself. This is still far from ideal. Even a few years ago, I’d noticed a few studies regarding T2 (diiodothyronine) and its metabolic effects in mice/rats. In the years since, I’ve read up on how bodybuilders take this hormone (effectively experimenting on their own bodies), how in high doses it’s TSH suppressive, and that it influences metabolism differently than T3.

      Now, how much of this hormone is in my medication? No idea (none if you’re on Synthroid/Levo, but I’m on Armor now so maybe some). How do my T2 levels compare to a normal person? No idea, you can’t even test for it!

      But why? If T2 significantly influences the lead diagnostic tools for diagnosing hypothyroidism and maintaining proper levels (TSH, free/reverse T3/T4), why is there no method to even determine if this is normal in thyroid patients, despite a large volume of subjective complaints post-medication?

      Risky bodybuilders + published literature alike have sound evidence at this point that taken in sufficient quantities T2 can both normalize TSH *and* cause some of the problems taking too much T3 can cause (which is why I called the bodybuilders risky – cardiac hypertrophy and screwing around with hormone levels isn’t something one lightly brushes off as risk factors… though to their credit they seem aware of the risks).

      If I wanted to do something stupid, I could probably get mostly normal thyroid ranges with a non-functional thyroid by buying over the counter T2 supplements… but let’s not do stupid things. The amount T2 influenced the rodents when compared against T3 varied between studies; a possible but no where near statistically confirmed trend is that it makes less of a difference in euthyroid rodents than hypothyroid… which even if true does not necessarily translate well to human beings.

      Unfortunately, there aren’t a lot of naturally hypothyroid voluntary self-guinea pig bodybuilders that are carefully tracking blood work as a result of mixing in T2 with other thyroid medication levels to see the weight loss results as compared against euthyroid people doing this.

      TL:DR – There is ample evidence to suggest interactions between hormones affecting thyroid patients that settled science does not understand, because it’s barely even looked at them. I would, however, be extremely wary of any physician managing thyroid levels if you ask them about T2/diiodothyronine (any of the types, there are multiple) and they claim it does nothing. At this point, the literature evidence alone is too strong for such an answer.

    • My doctor lowered mine from 112mc to 100mc and I am hoping I do not gain. I work out 5-8 hours a week and do not overeat dessert binges once in a while. I think I will change the way I take it also. Maybe before I fall asleep. I am curious to know how you do on the lower dosage.

  2. Hey guys, my symptoms just have me completely lost. I feel like another comment I read, you feel like you’re crying out to the Drs, and they think you are crazy. I’ve been on 50 synthroid for almost a year due to hypothyroidism. At the very beginning, I felt a bit better, but throughout the year I have been miserable!

    My doctor checks my TSH, t4, & t3 every 3 months, she says since my numbers are in normal range, she’s keeping on same meds/dose. I’ve begged her to understand, something is not right! GLOBS of my hair falls out, I literally cannot work full time because I can Barely stay outta bed, always tired.

    No family friends get togethers, and my weight is higher than ever and will actually move a few pounds only but only on the scales. My body fat will not move, even though I may lose some weight through diet and exercise, it simply only shows on the scale. My clothes and measurements are the same.

    I still get moments where I freeze! And a new symptom is my nerves are shot, like lately I feel like just simple things of every day living tears my nerves out of the frame! I’m literally at a loss, anyone have or had a similar situation on synthroid?

    I wanna stop taking it, but I’m kinda afraid to just stop cold turkey.

  3. This medication absolutely does make you gain weight. It raises your blood sugar and blood pressure too. For 6 years on it I couldn’t lose a single pound. But after having horrible side effects I decided to stop taking it against my doctor’s wishes and I lost 20 pounds!!!

    I also feel better off it than I ever did on it. Now I take vitamin D, K2 and lots of C everyday and do much better with that. Don’t let doctors tell you it’s all in your head!

    • I am experiencing the same thing! Are you noticing weight loss now? I immediately gained almost 10 pounds when I started it. They told me I was crazy. Thinking I should stop taking it as well.

      • Yes I lost 20 pounds really quickly without changing anything. My face is less puffy now too. I’ve learned on my own that a lot of times people get hypo symptoms because of vitamin deficiencies but doctors don’t really test for that. I started taking D3 and C and I think both have made a big difference.

  4. I’ve been on Synthroid 88 mcg for 6 months and have gained 10 pounds. My doctor says to eat better and exercise more and I have but no change. And the old song about you’ve never been 49 before, etc.

    But I know my body and this is totally new for me. I’ve never had a problem before taking this medication.

    • Try Armour Thyroid. It supplies both T3 & T4 from natural pig thyroid. I also gained weight while taking Synthroid and no doctor would listen. Finally I found one that did, changed to Armour, feel great and weight has stabilized back to normal.

  5. I had a total thyroidectomy in 2012. I was always very thin, active, ran 5 miles every morning before work, went to the gym daily after work. I worked in healthcare, I had a trainer, ate specified meals, etc. I have been on synthroid ever since. I have gone from 115 pounds at 5’2″. To 165 lbs!!!!

    I am miserable. Miserable… I cannot take anymore! I was on 75 then 88 then 112 now back to 100… I am always HYPO. They say, lower the dosage to raise the the thyroid level. From what I read on here, it seems that everyone who was put at 100 and more gained a lot of weight.

    This medicine has ruined my life. I have gut issues now, my hair is brittle, my skin is horrible. I sleep a lot. I’m seeing my doctor this week and I’m going to discuss maybe putting me back down to 75 and see what happens. They never check my other levels, T3 T4 or free T3.

    I hate to say this, but I feel better knowing that there are others out there who are experiencing the same thing. I know I’m not crazy…

    • I had a total thyroidectomy in 2011. Been on as much as 175mcg, mostly 150mcg, and currently at 137mcg. I am 49 and in the past 2 months (since switching to 137mcg), have gained 12 pounds!!! I feel SO big and uncomfortable!

      It seems every day my weight bumps up a little more. I’ve been walking every day for 40 mins, sleep hasn’t changed, nor has stress level or eating habits. I know my doc will say my thyroid numbers are right where they should be, but I’m tempted to say I want back on the 150. So very frustrating!

  6. I am a 63-year-old female and started on 112 dosage of Synthroid on 12/17/17 because of a total thyroidectomy. Initially I did not gain weight but have managed to gain 8 pounds in the last 3 weeks. I’ve noticed a dramatic increase in my appetite and cravings for sugar and carbohydrates.

    I am resuming a diet without gluten, dairy, sugar and processed foods to see if the weight will drop because I need to lose these eight pounds and can’t afford to gain any more weight!

  7. I started levothyroxine in Spring 2016 at 25 mcg. My doctor was initially great in gradually increasing my dosage as needed. In December 2017, she increased it to 88 mcg. I am still feeling tired, cold, foggy. I am now at my heaviest weight without much change in my diet since before the medication.

    I eat relatively healthy, and I walk my dogs every day and workout with weights and cardio 3-5 times per week. I’d say I easily gained about 20lbs+ due to my medication. I’ve asked my doctor multiple times to allow me to switch to another brand or add a T3 or switch to NDT. She instead referred me to a nutritionist and finally an endocrinologist. I’m at a loss for what to do… I feel awful about the weight gain and it’s so frustrating.

    • Very similar experience, 20 pounds even attempting to control diet. I have been a gym goer and diet watcher about 25 years with no change but the levo and weight gain. Doc says” Oh, it usually reduces weight.” This is not working for me.

  8. My psychiatrist did blood work on me and found my numbers went from 3 to 12 in six months. He sent his findings to my reg doc and he prescribed the Levothyroxine. Started me on 88 and trust me when I say, I had absolutely no reason as far as feeling sick or tired.

    I was moving at this time so I was pretty busy for the first two months and now I’m on my third month. My hair has thinned and I’ve gained 15 pounds in the tummy. IN 3 MONTHS!! My appetite has not changed, I eat once a day. No junk food for me but lots of protein from meat.

    I’ve always been around 116 or 118 lbs and am 5’2”. NOTHING in my life has changed. I decided last nite that that was the last pill I was gonna take. DONE!!! Oh, and when I asked what caused my number to shoot up like that? My answer was, “We don’t know”.

    • Hi. Have you lost any of the weight since your last pill? I’m overly curious as I’m 5’2 and have always weighed between 116-118 pounds. Am now 124.6 pounds!! I’m only on 25 mg of levothyroxine. Thanks!

      • Hi Jennie I don’t know if your reply was to me, but I quit taking it back in October and I lost 20 pounds almost instantly. I was shocked when I stepped on the scale. This is after years of exercising and starving and not being able to lose a single pound.

        I lost 20 without even trying and without changing my diet at all. All I did was stop taking levothyroxine. It makes me so mad because so many doctors told me it was my fault I couldn’t lose weight and that it wasn’t the medication.

      • Hi Jennie, Have you stopped taking levothyroxine? I am only on 25 mcg and I have gained over 20 lbs! I want to stop taking it but want to know if it worked for anyone? Thanks!

        • I am 67 years old and have been on Synthroid 25 mcg. about 10 years. I have gradually gained 10 pounds, heart palpitations, mild headaches occasionally and have little energy even though I walk 16-20 miles a week. Two days ago I stopped Synthroid.

          My TSH was never higher than 5.0 and I don’t think I should have ever been put on it to start. At this age I have read that anything under 8.0 is safe. This is crazy. I have lost 5 pounds already. Doesn’t make sense. It has to be the Synthroid.

  9. I took Synthroid for 1 year. Never felt worse and gained 16 pounds. I stopped taking the 100mcg of Synthroid and felt much better in a few days. Found another doctor. He put neon Armour Thyroid. 90mcg once daily and I feel great. TSH is where it should be and my weight has returned to normal. Synthroid provides T3, Armour provided both T3&T4 which some of us need. So try Armour if Synthroid is giving you problems. It works for me.

  10. I have been on levothyroxine for 2 years now. I was started on 75 mcg, then 88 mcg, and now at 100 mcg. With in months I started gaining weight like crazy. I never had weight issues prior to taking this drug and now I have packed on 55 lbs! I am convinced that it is the drug as I work out 4-5 times a week with a trainer. I lift weights and do a lot of cardio.

    My diet hasn’t changed much and any changes are actually more healthy than before. The doctors I’ve been seeing just will not hear what I’m telling them. I’m so frustrated at this point. So now I’m on the hunt for someone who will hopefully listen. Maybe an integrative/functional doctor. Any advice from is always welcome!

  11. My story is similar to Deborah and Leanne. I had thyroid cancer and thyroidectomy in 1984. I have been on synthroid since that time. I am currently alternating 100 and 112 mcg daily. I have been thin all my life. I workout several days a week, lift weights and run. Over the past 4 months, I have gained 8-10 lbs with no change in my activity or diet.

    I have increased my activity and reduced my calories and still have not lost any weight. In the past, weight loss has been easy for me. I also just received a call from my endocrinologist that my dose is reduced now to 100 mcg daily, but he is also ordering a complete blood work up. I don’t know if it’s the length of time I’ve been taking Synthroid or if it’s just my age (55 yrs), but I work hard to stay fit and I am very frustrated at the weight gain.

  12. I started taking Synthroid (Generic) 11/2016. After my levels normalizing, but not noticing any relief from symptoms – and weight gain from 162 to 169lbs. I asked my Dr about switching to non generic Synthroid and began taking that 01/25/2017. Since that time, I am still freezing cold all the time, my skin is cracking and painful, my sleep is terrible and my brain is foggy.

    Nothing has improved. Worst of all, I was 5’9 – 162 lbs when I started. This morning I weighed 180 – and I have don’t nothing different except work out more and improved my diet (which I started after the initial weight gain). If this is the way life will be, I will stop taking the medication and be hypothyroid.

    I may have all the same symptoms, but I will not be 20 pounds heavier! I am so frustrated and angry. Talk about depression – I didn’t have it before – but I may have it now.

  13. I have been on synthroid for 9 months and have gained 12 lbs! I exercise 150 minutes per week at the gym plus hike 3-6 miles on the weekend. I track my food and 4 years ago had gastric bypass surgery. In the 4 years since my bypass surgery my weight has been stable (no gain) but since the synthroid I am gaining weight. I am thinking it’s better to live with hypothyroid than to continue to gain weight. It’s frankly alarming after I worked so hard to take off 100 pounds.

  14. I started taking Levothyroxine in August after a year of fatigue and aches, and TSH level at 18. Since August, my dosage has increased to 200 mcg, and I have gained 17 lbs in 3 months. Diet and exercise hasn’t changed at all, in fact, I’ve had a decrease in appetite! Weight is mostly in bloated stomach and thighs – none of my clothes fit. My hair is now extremely dry (I’ve always had dry how, but now it’s even worse!!) any my eyelashes and hair are falling out!!! I go back for a follow up appointment on Monday… will post Dr. comments!

    • Hi there, I was on euthyrox 25 mg for 5 months, tomorrow will be my second week of not taking it anymore as the second doctor I have seen said I do not need the medication as my levels are now fine. I went for a second opinion as my appetite has dramatically increased these last months and I have gained a lot of weight due to the uncontrollable need to eat, even if I am not hungry or craving something, if food is close I feel moved to eat it. I have seen a psychiatrist but it is not due to emotions, I have never been in a better place in my live, no trauma and never an emotional eater, when I am stressed I have less of an appetite as normal.

      I thought I was loosing my mind then the doctor informed me that the medication can increase my metabolism making me eat more, or the whole day. I wonder how long it will take for it to be out of my system. I know there was another girl with a similar scenario and she said it took 3 months for her appetite to normalize. Does anyone have any advice?

  15. I am 44 and was dx with hypothyroidism when I was 19 so I’ve had it for 25 years. Started at a fairly low dose and seems like every 5 years or so adjustments needs to be made. I am a former athlete so am very physically active, eat well (I’m a dietitian), usually get my 7 plus hours of sleep and am not a “stressed” person. That all being said, I definitely have periods of unexplained weight gain.

    I’ll put on 5 lbs in a couple of weeks (so frustrating) and then have to work like crazy to try and lose it. We don’t know everything about this disease and I do believe the body has natural fluctuations and when the thyroid is not functioning optimally (those of us on synthroid), the body may not adapt to these occasional fluctuations. No research to support this but given my professional and activity background, I know this isn’t a result of my diet or activity.

    When these fluctuations happen, I almost fall asleep in the car and work, gain weight, get constipated, am exhausted and just feel like I’m in a hypothyroid state. Crazy enough when I get my bloodwork done, my TSH will be low (suggesting hyperthyroid) and my T4 is normal. My endocrinologist tells me some can get “synthroid-induced hypothyroid”. I’ve gone lower in my dose and it is seems to be the same. I’ve been as high as 175mcg and am now at 137mcg. I see my endo next week and just saw my result.

    Yup, low TSH and normal T4. Gained 5-7 pound in the last 2 months. I am sure she will lower it again. Hang in there everyone. Sometimes I feel like I am going crazy since my experience doesn’t follow the general literature. All I can suggest to all is stay the course (eat well, be active and sleep) and develop good relationship with your endocrinologist or GP. If they aren’t listening, find a new one. Good luck to all. I believe all of your experiences and know that what you are going through is real.

  16. I have been on Synthroid for 6 months and have gained 20lbs that I can not get rid of. An hour of constant jogging/running every morning and every evening on the treadmill, eating fruits and vegetables all day with a modest healthy dinner has not resulted in one lb being dropped. I complained to my Primary Dr who could not even understand what I was complaining about.

    All he kept saying was exercise, you didn’t get this weight gain from Synthroid. I went to see an Endocrinologist who attributed my fatigue to sleep apnea (really?!) and raised my synthroid to 100!… No one listens to me about how this weight gain (and hair loss… have I mentioned the hair loss!) is from the medicine and I hate that I have lost all input into how I should be treated.

    I am made to feel like an idiot when I try to tell the doctors how depressed I am, but when no one wants to understand what is happening to you, or cares to discuss it, or even acknowledge it, it makes the depression more difficult to handle.

  17. I was diagnosed with hypothyroidism in 2007 and have been on Levothyroxine since. I am now 52 years old and am stuck at 185 lbs. Luckily I’m 5’8″ so it doesn’t look as bad however, my Dr. said I’m overweight and need to go on a diet because I should weigh 164! Well that would’ve never been a problem if I didn’t have this thyroid issue.

    I go to the gym and water aerobics an hour each, three times a week and I volunteer in the horticulture department at our local gardens. I get at least 10,000 steps a day and eat lots of vegetables, protein and some fruits, but no change whatsoever; even with portion control.

    The Dr. just keeps saying the same thing over and over “Your thyroid levels are good, you just need to diet and exercise”; I could scream!!!! Anyway, it’s gotten to the point that I don’t feel as if it’s worth killing myself when I see no results. I’m very depressed over it.

  18. I have been on thyroxine for approx 1 year post thyroidectomy for metastatic papillary cancer. I started on 100mg then they increased it to 150mg to keep me in a suppressed state following radiation therapy for recurrence. Over a period of 12 months, I have gained over 10kg in weight and am still going. I feel like I am never going to stop. Although my blood readings show I am hyperthyroid, I have all the symptoms of hypothyroid. Help.

  19. I have battled thyroid issues for 14 yrs. It began with rapid weight gain. I had always been extremely thin (115 lbs when I was 45). By the time I was 46 I had gone up to 160 lbs and my doctor told me “face it, you are getting older” but she did a blood test that showed hyperthyroid and sent me for a scan where a nodule was found and I was diagnosed with Graves disease.

    My thyroid was removed at age 47 and I was at 180 lbs. I was prescribed 80 mg of synthroid and increased to 223 lbs within the next 2 years. I was miserable…the weigh gain happened so quickly it felt as if my ribs ached from spreading to make room for the fat; my feet ached if I walked on them and my lower back pain caused me to walk stooped over to try to relieve the pain. My endo simply stated that I would not need to see him again if the next blood test came back in the “normal range”.

    I told him he needn’t worry…that he wouldn’t see me again and I never went back. After several attempts at doctor shopping to find they refused to listen and one simply handed me a sample bottle of cymbalta. By the time I was 52, I finally found a doctor that listened to me and on the first visit I had copies of my previous blood work and he stated I was very hypo. He explained that he uses blood tests but also the way I feel to determine the appropriate medication and dosage.

    I told him about the synthroid weight gain and he changed me to levoxyl and at some point unithroid and I was on 175 of each of those. With time I learned to change my diet and eating habits and proudly weighed 155 by the time I was 57. I watched my diet but managed to stay in the 155-160 range for 4 years. Now due to insurance I can no longer see that doctor and had to change.

    Over the last year I have gained 20 lbs. The new doctor did blood work and reduced the levothyroxine to 150 and now 125. The doctor says he does not see where I have gained an extreme amount of weight. I weighed 172 when I first started seeing him in March. I now have to eat basically one meal at day…a healthy lunch…to keep my weight at 180 but I have been up to 183 if I eat in the evening.

    I also have COPD and take a corticosteroid inhaler daily…they also say that does not cause weight gain. Now I am reading that thyroxine actually causes some individuals to gain weight…but I am not seeing any alternative other than armour. Always searching for answers and help in order to live a “normal” life… and a doctor that will listen!

  20. I have been taking 125 mcg levo upped dosage myself. Mostly ignore GPs as find they’re not overly interested in thyroid patients. Have to practically beg to have my blood done and when I ring for results usually get told its normal when TSH is around 5. Receptionist last time I rang, didn’t even know what TSH was!!

    Maybe they don’t like us as we get our medication for free? Believe me its not by choice I take levothyroxine, think its a horrible drug. I too have put on weight particularly round belly and thighs, like fluid retention. Its called levothyroxine SODIUM, and what does sodium do? Causes fluid retention.

  21. Started out severely hyperthyroid, Graves’ disease. Dr’s decided that ablation would be the route to take, and during this time I actually gained weight. I went from 119 to 150 in 9 months. When I finally went from hyperthyroid to hypothyroid I gained another 15 lbs in a month and have been on Synthroid for a few weeks. I’ve seen a few lbs drop but was just informed by my Dr that I will probably gain some weight and if it gets “too significant” to call her but otherwise I have to wait 12 weeks for an up in dosage.

    She never explains anything, I have no idea what to expect or where I’m going with my condition and I’m pretty lost in this T4 T3 thing. She’s horrible and the first dr was worse. He told me since I was gaining weight and it wasn’t a symptom of hyperthyroid then I must be over eating. I’m a pretty active 5’2″ 39 year old, averaging 16,000 steps a day, gym 5 days a week before this all started and eat pretty well.

    I just need answers. Am I going to gain another 40lbs? I’m packing on the lbs and it can’t be good for someone so short right? Help.

  22. I had a slightly low T4 level, a 4.3. I asked my Doctor if I needed to pay attention to that since both my mom and my sister have sever Hypothyroidism. He thought we could try a low dose of Synthroid. Started .25 mcg back in June. Since then, I have gained about 6 lbs. I watch what I eat and exercise. This is very frustrating and mostly because I am not sure I even needed the meds to begin with.

    My previous Doctor thought I didn’t need anything and there was nothing to worry about. Not sure how this will affect me long term but as of today, I stopped the medication. Hoping that with my healthy lifestyle, my weight will go back to what it was. I am 45 years old, 5’4″ and was at about 150lbs before all this. Hoping that I stabilize and just get back to normal.

  23. I have also had the weight gain and try as I might, can’t lose an ounce. I never weighed much over 125 but add 50 pounds and wow. Never thought I would have a weight issue. Took my calorie consumption to 800 per day. Go to the gym, walk, etc etc just like everyone. Weight is not moving.

    Quit taking the meds and the old symptoms came back for the hypo. Even my hair falling out, etc. Started taking it again. Amazing all the symptoms went away. Turning 60 next year and I DO NOT want to head into the 60’s carrying the extra weight. Any suggestions?

  24. I have been taking levothyroxine for past 3 months. Began on 25mcg then bumped to 50mcg after 6 weeks. I have noticed a steady weight gain of about 4-5 lbs over that time. No significant changes in diet or sleep (I have a toddler so it’s not great…) and have actually improved my exercise habits in an attempt to stave off this weigh gain, to no avail.

    My endocrinologist looked at me skeptically when I mentioned the weight gain at my last appointment, so it’s nice to find this article. Reading the article, I wonder if my gain is water/bloating, as it has mainly affected my waist and my thighs a bit. We’ll see in a few more months… If I knew it would level out I could live with it (and buy some new clothes!)… but going to be very stressful if it keeps increasing.

  25. I am commenting to add my voice to the anecdotal evidence of an unexplained weight gain associated with taking Levothyroxine. I am available to discuss further by email.

  26. I have been on Levothyroxine for about four years now and have gained about 20 pounds which will not come off whatever I eat (or don’t eat). Most of it is carried on the front so I look pregnant and can’t wear any of my jeans. Skirts ride up and sit around the lower ribs. The Endo has gradually increased the dose to now 100 micrograms and energy is a little better.

    I’m arguing with him to get him to add T3 to the mix to see if it makes any difference to my energy levels and the weight. I also have episodes of vertigo which I understand can be linked to hypo. If I reduce the levothyroxine dose the thyroid becomes uncomfortable, feeling swollen. I was only tested for hypo when an MRI for something else showed a large nodule on the thyroid.

  27. I have been on synthroid for 6 years and have gained 30 pounds in that time. Before synthroid, I was always thin and fit. Now I starve and exercise like crazy and the weight just doesn’t come off. I also started experiencing hyper symptoms and felt so tired and fatigued all the time. Two weeks ago I decided I’m not taking it anymore. I already have more energy, am sleeping better and feel thinner. My belly looks smaller too.

    • How are you feeling now since you posted this in June of last year? I am desperate and continue to gain weight yet I am so very diligent on what I eat and exercise on a regular basis. Been on a high dose of Synthroid for many years. I am fed up.

  28. These comments have been so helpful. I’m 2 years post total thyroidectomy and being 32 at the time I just assumed it was an age vs. metabolism issue. I’ve always been active and had a great metabolism. Since synthroid I’ve had a steady gradual increase of weight – even when I reduce/burn more calories. I would love to know what could be done to change this.

  29. I’ve been on for 6 years, low dose .25mg. The month my doctor upped me to 100mcg I gained 50lbs in 3 months!! My life was great, I had no stress or worries. I’m a vegan and have a trainer… I 100% believe I gained weight from synthroid. Not only that, I started having daily migraines. My neurologist suggested I get off the drug, and boom! More energy, no migraines in 2 weeks.

  30. My first experience with levothyroxine began in 1998, after a CT revealed benign nodules all over my thyroid. I did not initially gain weight, in fact lost a few pounds with this treatment. After several years my bloodwork and symptoms seemed to be indicating that Levo – was no longer as effective as it had been, and I was switched to Armour Thyroid.

    Being totally vegan, I objected, but my symptoms of insomnia, freezing in 90 degree temps, and fogginess were so overwhelming that I gave in to this path of treatment. It was a very successful course of treatment for over 5 years for me. My insurance company recently decided to stop covering Armour, so my MD switched me back to levothyroxine. (Insurance will not approve visit to endocrinologist until we start over with the step-by-step standard treatment plan, which makes me furious!)

    Within 3 weeks I am now up 12 pounds with zero change to my extremely active lifestyle (no less than 5 miles per day – typically more, plus yoga, weights – kettle bells daily and outdoor activity with my kids) and zero change to my vegetable – heavy, plant-only diet. I’m floored at the rapid weight gain and severely uncomfortable bloating and constipation.

    I have to assume it’s the change in my gut microbiota, due to the components in the Levo – and I’m disgusted. I am nearing 45 years-old, so I’m afraid I am beginning to fall into the above mentioned age-bracket of sample patients in article. Thank you for this well-written information and I wish the best to all of you seeking treatment!

    • The same as me!!! I’m also vegan and active, I gained 50lbs in 3 months and can’t get it of me! I just stopped taking it, feel amazing!!! Got the BioTE pellets instead and life is great!

  31. I’m 5 weeks post total thyroidectomy with removal of one parathyroid gland that appeared necrotic, and was implanted back into the sternocleidomastoid. I’m on levothyroxine 112 mcg, started a few days after surgery. I have gained 30 pounds in 5 weeks. Pending an appointment with my endocrinologist I increased the levothyroxine to 140 mcg, thinking that might stop the weight gain but it hasn’t.

    I did have a small adenocarcinoma that was completely removed. I was only able to see the NP, not an MD at the endocrinologist’s office who did not know why I gained weight, didn’t know if related to the levothyroxine or change in dose. She basically was not able to answer ANY of my questions, so I’m researching as this weight gain, sometimes several pounds a day, has GOT to stop.

    My fear is that I have returned to my old hypothyroid metabolism where I had to reduce calories down to below 499-800 a day to lose weight. My diet is very low fat and under 1200 calories a day. Exercise is weed whacking, weeding and caring for livestock and gardening, which I barely have energy for now. I’d appreciate any suggestions! Thank you for a great article!

  32. I have been on Synthroid since 1996 when I had a total thyroidectomy for treatment of thyroid cancer. I definitely believe being on Synthroid has caused weight gain and increases the ability to remove it. I am a very active person and since 1996 have completed marathons, half-marathons, week long bicycle rides, as well as exercise every day and I stand and walk all day for work.

    On a typical work day I get 17,000 steps just by going to work. I also lift weights, do Pilates, some yoga, bicycle, hike, garden, snow shoe and just about anything else active. I eat lots of vegetables and greens. I limit fruit and sugary things, I don’t put sweetener in my beverages. I drink water, sparking water unsweetened or unsweetened green tea.

    I eat lean proteins and limit starches. I focus on whole grains like Ezekiel Bread which is sprouted grain. If I eat a protein bar it’s usually Quest brand, as it is low in sugar. I do eat dark chocolate and occasionally have ice cream. I am very educated in healthy eating and I continue to update. Regardless of any of what I do, I can put on weight.

    I am trying to spend more time relaxing but I honestly don’t feel stressed out. I have always felt like something has never been quite right once my thyroid was taken out. I cannot explain it and I don’t know how to describe it to a doctor, but something changed and it has never gone back to what I would say normal.

    My grandma had a goiter and she struggled with weight all the time. I don’t even say anything to the doctor anymore because they don’t listen and at the end of the day I don’t have cancer and I have two arms and two legs and if it’s the worst thing. That’s going to happen then that’s not that bad, but it would be nice to figure it out one day.

    • You sound like me. I am an exercise participant doing all you do all my life. I am strong in body and cardio but have too much body fat for the effort and food. My body is turning to fat and I eat similar to you above. All my family went on whole 30 and I did all the preparation. They lost 10 to 15 lbs and I gained for a bit. My doctor just told me he is lowering my dose so now I feel I will gain more…


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