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Synthroid (Levothyroxine) & Weight Loss: A Common Experience

Synthroid (Levothyroxine) is among the most popular pharmaceutical medications in the United States; over 120 million prescriptions were filled for the drug within the past year.  It is a synthetically engineered form of thyroxine (T4), an endogenous thyroid hormone produced by follicular cells within the thyroid gland.  Among individuals diagnosed with hypothyroidism, the body is unable to produce adequate T4 (thyroxine) via the thyroid gland, which has deleterious effects upon DNA transcription, protein synthesis, and a multitude of neurophysiological processes.

As a result, individuals with hypothyroidism often exhibit symptoms such as: cognitive deficits, depression, dry skin, fatigue, malaise, and weight gain.  Regular administration of synthroid (levothyroxine) is thought to reverse the aforementioned symptoms of hypothyroidism and improve functionality of the user.  After several months of properly-dosed synthroid, users often report: clearer thinking, increased energy, mood improvements, and perhaps most noticeably – weight loss.

Weight loss is often among the most discussed synthroid side effects due to the fact that nearly everyone wants to look good and maintain a healthy physique.  Additionally, many individuals had gained a significant amount of weight prior to using synthroid (as a result of hypothyroidism), a condition which slows metabolism.  When metabolic processes are corrected as a result of synthroid, users end up losing weight and the weight loss comes as a pleasant surprise.

Synthroid (Levothyroxine) and Weight Loss: A Common Experience

If you’ve lived with hypothyroidism, there’s a chance that you may have gained some weight as a result of the condition.  The chief purpose of thyroid hormone is to regulate the body’s metabolism, and when an individual is struggling with a thyroid deficiency, basal metabolic rate (BMR) plummets.  Individuals with hypothyroidism may: cut calories, eat a healthy diet, exercise plenty – yet still end up gaining weight due to their slower basal metabolic rate; fewer calories are being burned at rest.

During treatment with synthroid, the body receives a synthetic version of thyroxine (T4) which upregulates the hypothyroid-induced metabolic downregulation and facilitates weight loss.  Users that are prescribed an optimal dosage of synthroid should lose all weight that was gained specifically as a result of their hypothyroidism.  Weight loss from synthroid is usually most prominent during early stages of synthroid treatment because the body hasn’t yet adapted to the increase in basal metabolic rate (BMR).

As synthroid treatment is continued for an extended duration, the body will have adjusted to the increase in basal metabolic rate (BMR), and additional weight loss will subside.  For some users, weight loss may subside after a few months of treatment, yet for others it may take a year for the weight loss to diminish.  The amount of weight loss that occurs from synthroid, as well as how quickly it occurs, will likely be contingent upon how long you lived with untreated hypothyroidism and the severity of your hypothyroidism.

How Synthroid (Levothyroxine) May Cause Weight Loss

There are many possible ways in which synthroid may contribute to weight loss.  In most cases, weight loss resulting from synthroid usage should be chalked up to the fact that it corrects an abnormal and/or dysfunctional basal metabolic rate (BMR) associated with hypothyroidism.  It is the correction of BMR (by promoting an increase) that leads to weight loss.  Other ways in which synthroid may cause weight loss include: appetite reduction, cognitive enhancement, increased energy, altered neurotransmission, and side effects (e.g. diarrhea).

  • Appetite reduction: Many synthroid users report that the drug decreases and/or suppresses their appetite. Assuming you feel less hungry than usual while taking synthroid, there’s a good chance that you’ll probably eat less food and end up losing some weight.  In a subset of individuals diagnosed with hypothyroidism, an overwhelming appetite is problematic and leads to constant overeating.  Synthroid administration may reduce a large appetite and decrease the urge to eat.
  • Cognitive function: It is understood that those with hypothyroidism often exhibit brain fog, inability to think clearly, and poor cognitive function. As a result, many people with hypothyroidism make impulsive food choices and lack a nutrient-dense diet.  Poor nutrition exacerbates existing cognitive deficits and perpetuates future suboptimal dietary choices.  Upon correction of hypothyroidism-associated cognitive deficits (as a result of synthroid treatment), individuals are able to make better decisions about the foods that they consume and exert more overall self-restraint to avoid unhealthy food choices.
  • Decreased food cravings: In some individuals, hypothyroidism may contribute to food cravings, especially for junk food (e.g. artificial sweeteners, sugars, simple carbs, etc.). With regular administration of synthroid, some individuals may find that food cravings subside.  You may feel as if you no longer are constantly craving carbs, cookies, candies, etc. – all throughout the day.  Assuming you have fewer overall food cravings, you’re likely to consume less unhealthy “junk food” and could end up losing some weight.
  • Energy increase: There’s a stark contrast in the energy level of an individual with an optimally functioning thyroid and someone who’s suffering from hypothyroidism. Most individuals with hypothyroidism slog through the day with considerable fatigue and grogginess, making it challenging and less appealing to stay active and/or exercise.  When taking synthroid, your energy level may skyrocket (compared to what it was) and you may end up going to the gym, moving around more, etc. – all of which can burn calories, enhance your metabolism, and contribute to weight loss.
  • Ghrelin reduction: A hormone responsible for regulating hunger, known as “ghrelin,” is abnormally high among individuals with hypothyroidism. Ongoing administration of levothyroxine (synthroid) appears to significantly reduce ghrelin concentrations.  It is possible that the reduction of ghrelin as a result of synthroid administration leads users to feel more satiated with fewer food cravings than usual. (Source: http://www.ncbi.nlm.nih.gov/pubmed/23339003)
  • Gut bacteria: There is some evidence to suggest that some cases of hypothyroidism may be caused by small-intestine bacterial overgrowth (SIBO) within the gut. It is known that a person’s gut bacteria can be predictive of whether they’re likely to lose or gain weight from eating a certain set of foods.  One person with a specific gut microbiome may differ significantly in terms of weight loss/gain from a particular food – than a person with a different gut microbiome.  It may be necessary to consider that administration of synthroid may alter a person’s gut microbe in such a way as to promote weight loss.
  • Metabolism increase: The primary reason synthroid users experience weight loss is related to an increase in basal metabolic rate (BMR). As was already discussed, individuals with hypothyroidism tend to exhibit abnormally slow basal metabolic rates.  When synthroid is taken, basal metabolic rate is corrected (or normalized) and weight loss occurs without much effort.  This may result in weight loss without any change in lifestyle, dietary intake, etc.  When you’re burning more energy at rest as a result of an increase in basal metabolic rate (compared to pre-synthroid treatment), weight loss is likely to occur.
  • Neurochemistry: There is evidence to suggest that synthroid (levothyroxine) affects neurotransmission and neural activation (of particular regions). For this reason, it should be hypothesized that altered concentrations of neurotransmitters (e.g. monoamines) and/or changes in neural activation following synthroid administration – may contribute (directly or indirectly) to weight loss.  It is understood that neurochemical changes can affect propensity to lose weight.
  • Placebo effect: It may be necessary to consider that in a subset of synthroid users, the placebo effect contributes to weight loss. Some individuals may expect to lose weight while taking synthroid, and the weight loss becomes a self-fulfilling prophesy.  Since the scientific literature reports that synthroid isn’t associated with significant changes in body weight (on average), yet many users still report weight loss – the placebo effect should be considered a potential contributing factor.
  • Side effects: In some cases, users of synthroid may experience weight loss as a result of other side effects. For example, if synthroid is provoking round-the-clock diarrhea, the laxative effect will likely contribute to some degree of weight loss.  Additionally, it could be that synthroid causes nausea and/or stomach aches – each of which may interfere with a person’s appetite, resulting in reduced food consumption.  Consider that some of the weight loss may stem from other side effects, especially if they are severe.

Note: Although weight loss from synthroid is thought to primarily stem from increases in BMR, other potential causative factor should not be dismissed.  Furthermore, the exact causes of synthroid-induced weight loss may be subject to interindividual variability.  One individual may lose weight while taking synthroid primarily from BMR increases and diarrhea, while another may lose weight due to the fact that synthroid increased his/her energy enough to maintain a daily fitness routine.

Variables that may influence weight loss from Synthroid (Levothyroxine)

There are variables that may influence a bulk of synthroid-induced weight loss that you experience.  These variables include things like: synthroid dosage, duration of administration, co-ingested medications, and other individual factors (e.g. stress level, sleep quality, etc.).  When contemplating how much weight you’re likely to lose while taking synthroid, it may be helpful to consider these variables.

  1. Synthroid Dosage

The amount of synthroid that you ingest on a daily basis can affect how much weight you’re likely to lose.  The dosage is determined based upon the severity of an individual’s hypothyroidism, as well as his/her body mass index.  In any regard, those taking higher doses of synthroid are likely to lose more weight than those taking extremely low doses.

This is due to the fact that high-dose users are likely to have severe hypothyroidism.  Severe hypothyroidism may have resulted in significant weight gain prior to synthroid treatment.  As a result, when the individual pursues synthroid treatment, he/she has a lot more weight that is easily lost upon treatment with levothyroxine (synthetic T4).

Additionally, the higher the dosage administered (based on a person’s body size), the greater the neurophysiological effect resulting from synthroid.  When administered at too high of a dose, users may exhibit symptoms akin to hyperthyroidism, abnormally high BMRs (basal metabolic rates), and weight loss.  The greater the dosage you’re taking, the more likely you are to end up losing some weight.

Those taking low doses of synthroid such as for subclinical hypothyroidism are less likely to lose a significant amount of weight.  This is due to the fact that subclinical hypothyroidism is unlikely to cause significant weight gain in the first place.  Since lower doses exert a less substantial neurophysiological effect, BMR may only increase to a modest extent – leading to a small amount of weight loss.

  1. Time span

The duration over which you’ve been taking synthroid can affect how much weight you lose.  Most individuals with severe hypothyroidism report noticeable weight loss after several months of treatment (e.g. short-term).  In some cases, this weight loss may continue over a longer duration as dosage is reassessed and/or readjusted.  In other cases, weight loss may be limited to a short-term and may gradually diminish and/or cease with a longer-term of synthroid treatment.

Short-term: Taking synthroid over an extremely short-term (e.g. a couple days) may not be long enough for noticeable weight loss.  However, most individuals end up noticing some degree of weight loss after several weeks of synthroid treatment.  Short-term weight loss is common due to the fact that your body is adjusting to a faster BMR as induced by the synthetic thyroxine (T4).

Long-term: Over a long-term of treatment, weight loss from synthroid is likely to subside.  You may end up losing weight gradually over a period of months, but eventually your body will adjust to the regularly administered, daily dosage of synthroid.  Following neurophysiological adjustment to synthroid, weight loss tends to diminish and body weight is often maintained.  Additional weight loss after a long-term of treatment may occur among those who are subject to further increases in dosing.

  1. Hypothyroidism details

To understand how much weight you’re likely lose while taking synthroid, it may be necessary to reflect upon the details of your hypothyroidism such as: how long you’ve lived with it and its severity.  If you’ve been living with undiagnosed and/or untreated hypothyroidism for an extended duration, you may have gained a significant amount of weight as a result.  This means you’ll stand to lose more weight during treatment with synthroid.

It is also important to consider that if your hypothyroidism is only of mild severity, it may not have significantly altered your weight in the first place.  Since mild or subclinical hypothyroidism is often treated with low doses of synthroid, weight loss from treatment may be unnoticeable and/or insignificant.  Those with severe hypothyroidism taking high doses of synthroid have the greatest chance of losing weight.

  1. Co-administered substances

It may be necessary to consider that co-administered medications and/or supplements may affect how much weight you lose while taking synthroid.  Some medications are known to interfere with the absorption of synthroid, leading to suboptimal therapeutic outcomes.  Most medical professionals instruct patients to avoid certain drugs and/or supplements (e.g. multivitamins) while taking synthroid.

Co-administered substances may potentiate and/or inhibit weight loss associated with synthroid.  For example, someone prescribed a pharmaceutical psychostimulant (e.g. Adderall) may lose weight from both the synthroid and the psychostimulant.  It may also be necessary to consider that another medication and/or supplement that you’re taking is responsible for nearly all of the weight loss that you’ve experienced on synthroid.

Many people automatically assume that synthroid caused weight loss, without considering that it may have been from an entirely different pharmaceutical.  That said, if you don’t experience much weight loss from taking synthroid, it is possible that another medication and/or supplement is causing weight gain, thereby interfering with synthroid-induced weight loss.  Consider that synthroid and another substance may be effectively “canceling each other out” – resulting in weight neutrality or no change in weight.

  1. Other individual factors

Everyone is quick to automatically assume that synthroid is the sole influencer of weight loss without considering critical individual factors.  Individual factors that should always be considered as affecting synthroid-induced weight loss include: dietary intake, exercise, genetics, sleep, and stress level.  Someone who starts taking synthroid, but also begins eating healthier, exercising frequently, getting better sleep, and lowering his/her stress – may experience weight loss from lifestyle changes.

These lifestyle changes may compliment the weight loss induced by synthroid, resulting in a more significant change in physique.  On the other hand, someone who uses synthroid and: eats junk food, doesn’t exercise, fails to manage stress, and is sleep-deprived – may not lose any weight.  Why? Because poor lifestyle habits such as sleep-deprivation are known to cause weight gain.

When taking synthroid you may want to consider how your lifestyle may have played a role in the weight loss.  It should also be noted that genes (and expression) may make you more or less likely to lose weight from a medication like synthroid.  Individuals with a particular gene (or lack thereof) may not lose any weight during treatment, while others with certain genes may lose a significant amount in response to the medication.

Synthroid (Levothyroxine) & Weight Loss: The Research

Although many individuals report losing weight while taking synthroid (levothyroxine), the scientific literature suggests that weight loss is unlikely.  That said, there are only a few published studies investigating the effects of synthetic thyroxine (T4) on body weight.  Additionally, some of these studies were conducted in horses rather than humans, making it difficult to draw any relevant conclusions.

2014: Changes in body weight after treatment of primary hypothyroidism with levothyroxine.

A study conducted by Lee et al. (2014) investigated the effect of levothyroxine (LT4) therapy on body weight of hypothyroid patients.  Researchers specifically sought to determine the significance of weight changes after LT4 treatments were initiated for primary hypothyroidism.  They set-up a retrospective cohort study that took place from January 2003 to February 2011 consisting of adults diagnosed with primary hypothyroidism.

A total of 101 participants completed the study, each of which had TSH levels exceeding 10 mIU/L.  Prior to treatment with levothyroxine, researchers recorded participants’ weight and TSH concentrations.  Approximately 24 months after the initiation of levothyroxine treatment, body weight and TSH levels were reassessed and compared to (pre-treatment) baseline recordings.

Results indicated that baseline average weight was around 175 lbs (79.6 kg) and after 5 months of levothyroxine treatment, average weight change was 0.22 lbs (-0.1 kg).  Of the 101 participants, 52% lost weight – average weight loss was 8.4 lbs (3.8 kg).  Researchers concluded that no significant changes in weight occur after initiation of levothyroxine (LT4) treatment.

  • Source: http://www.ncbi.nlm.nih.gov/pubmed/24936556

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

A study conducted by Ozdemir et al. (2010) investigated the effect of thyroxine on body mass index (BMI) and body composition among patients who underwent a total thyroidectomy.  Researchers noted that many thyroidectomy patients report weight changes and/or changes in bodily composition after the procedure.  A total of 33 patients were recruited for the study, but only 22 individuals completed it (5 males, 17 females, ages 26 to 64 years).

Following the thyroidectomy, levothyroxine was administered at 50-200 mcg based on the particular patient.  Dosages were adjusted based on postoperative plasma TSH, FT4, and FT3 levels – 3 weeks after surgery.  After treatment with thyroxine, researchers recorded changes in: body weight, body mass index (BMI), and other physical measures.

Results indicated that levothyroxine administration had no effect on body composition.  However, it appeared as though body weight was significantly altered by levothyroxine among the 14 participants over the age of 45 (ages 46 to 64).  In the older adults, levothyroxine administration increased boy weight by an average of 4.85 lbs (2.2 kg).

Younger individuals (under the age of 45) didn’t appear to experience significant weight changes.  Evidence from this study suggests that levothyroxine may cause weight gain in older adults (rather than weight loss).  Since the study was small-scale with limited numbers of participants, it is unclear as to whether the results of the study accurately reflect weight changes among older adults taking levothyroxine; further follow-up research is warranted.

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

2008: Effects of long-term oral administration of levothyroxine sodium on serum thyroid hormone concentrations, clinicopathologic variables, and echocardiographic measurements in healthy adult horses.

A study conducted by Frank et al. (2008) sought to determine the effects of long-term oral levothyroxine (LT4) administration in adult horses with normative thyroid function.  For the study, researchers utilized a total of 6 healthy adult mares.  All horses were administered 48 mg per day of levothyroxine for a duration of 48 weeks.

Physical examinations of body weight were performed in 4 week intervals throughout the entire 48-week term.  Throughout the 48-week term of treatment, horse body weight significantly decreased when compared to pre-treatment baseline.  Results indicated that after 48 weeks of treatment, average horse body weight had decreased by 55 lbs (25 kg).

Additionally, researchers noted that by the end of the 48-week term, insulin sensitivity had significantly increased by approximately 1.9-fold.  The greater the extent to which insulin sensitivity increased, the more significant the amount of weight loss that occurred.  Researchers concluded that levothyroxine significantly reduces weight in healthy adult mares and may be helpful for the treatment of obesity and/or insulin resistance.

It should be noted that results from an animal (horse) study cannot and should not be generalized to humans.  That said, it is possible to consider that humans who lose weight while taking levothyroxine may experience increases in insulin sensitivity.  Since this study was conducted in healthy (euthyroid) horses, it is unclear as to whether similar effects could be observed among horses with hypothyroidism.

  • Source: http://www.ncbi.nlm.nih.gov/pubmed/18167090

How much weight will you lose while taking synthroid (levothyroxine)?

There’s no set amount of weight that you can expect to lose while taking synthroid.  Published studies in humans suggest that weight loss associated with synthroid treatment is unlikely.  As of now, there is no significant evidence to suggest that you’re likely to lose weight from regular synthroid treatment over a period of 5 months.

There is some evidence to suggest that a subset of synthroid users may actually gain weight, particularly those who are “older adults” (ages 45+).  However, there are numerous variables that should be considered whenever contemplating how much weight you’re likely to lose (or gain) while taking synthroid.  Synthroid should be capable of reversing any weight you had gained as a result of hypothyroidism-induced metabolic changes.

If you believe that you gained around 20 lbs from untreated hypothyroidism, synthroid treatment should help you lose the 20 lbs.  That said, synthroid will not reverse weight gained from things such as: eating unhealthy, excess calorie consumption, lack of exercise, high stress, poor sleep, and/or taking another medication.  If you’re unable to lose weight from synthroid, it could be that your dosage is too low, you haven’t taken it for long enough, and/or the weight loss is being offset by an aforestated variable.

Does everybody lose weight while taking synthroid (levothyroxine)?

No.  Clearly not everyone ends up losing weight from taking synthroid.  While weight loss is more commonly reported than weight gain, it is not a guaranteed side effect.  A subset of synthroid users remain relatively “weight neutral” or don’t fluctuate in body weight to a significant extent as a result of the medication.

Another percentage of users may actually gain weight as a result of synthroid.  Whether you lose weight while taking synthroid may be contingent upon variables such as: your dosage, duration of treatment, and/or other medications ingested.  Someone taking synthroid along with a psychostimulant may end up losing weight from the synergistic combination (each of which increase BMR).  Other users taking antipsychotics may gain weight because the antipsychotic has a propensity to decrease BMR.

If you’re taking synthroid and/or about to start treatment, don’t expect any weight loss.  Simply expect the medication to correct many of the neurophysiological abnormalities associated with hypothyroidism.  The goal of synthroid treatment is to improve compromised functionality and/or well-being associated with hypothyroidism – not to lose weight.

Have you lost weight while taking Synthroid (levothyroxine)?

If you’ve taken synthroid, leave a comment mentioning whether you lost weight as a side effect.  To help others get a better understanding of your situation, share some details such as: how much weight you lost while taking synthroid and how long it took to lose the weight.  Discuss whether you believe that synthroid directly caused the weight loss OR whether synthroid indirectly helped the weight loss such as by giving you more energy to work out and/or make better decisions about foods that you eat.

Did you perceive the weight loss as being a favorable aspect of treatment?  Or were you already relatively skinny/small-statured and perceived the weight loss from synthroid as being unwanted?  Understand that if you’re a new synthroid user and haven’t been taking it for a long-term, you may lose weight over a period of months, but the weight loss may decline and/or subside thereafter.

This is because after awhile, your body adapts to the increase in BMR and neurophysiological stimulation provided by the synthroid.  Shorter-term users are more likely to report major weight changes, but it is unclear as to whether these weight fluctuations can be maintained.  To better understand individuals that are likely to lose weight from synthroid (levothyroxine), there is a need for additional scientific research.

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28 thoughts on “Synthroid (Levothyroxine) & Weight Loss: A Common Experience”

  1. I’m 37 and found out 3 weeks ago that I’m hypothyroid. I was started on 50mcg and increased to 100mcg a week later. From Day 7 to day 21 (2 weeks) I have lost 1kg.

  2. I have been on synthroid since 1996. Prior to that I gained 30 lbs in a year when I finally found out I had a thyroid problem. Even 6 years after I had my 2 children, I still only weighed 120 lbs before the thyroid problem hit me.

    I have never experienced any weight loss anytime while taking this medication for 22 years. And over those 22 years, I still experienced some of the effects of hypothyroidism like not remembering things (brain fog), cannot tolerate the cold, and depression. They say I’m on the correct medication, but I don’t feel I am!

  3. I was prescribed Levothyroxine about 1 & 1/2 years ago and started losing weight. I didn’t care about this because I normally lose weight in the Spring and Summer and regain it around Christmas. I lost about 25 pounds and didn’t regain it last Christmas. This is still no big deal because I see no effects from it except needing to get some smaller blue jeans.

  4. I had 1/2 my thyroid removed in Dec. 2017 and was put on 50 mcg Synthroid. I have only lost 7 lbs so far but am afraid I will lose a lot of weight as I’ve been thin all my life. Is there anything I can do to counteract the weight loss?

  5. My 97 year old mother was diagnosed Hypothyroid and was started on Levothyroxine Sodium 25 mcg per day. She is also on diuretics to control her leg edema. She has lost a total of 45 pounds since Feb 3.

    Before she had her room up to 82 degrees and blankets on. Now her room is 76 and she’s using one blanket. Her Sodium was 98 and now it’s 136. She has more energy and feels good. The weight loss is a little bothersome.

  6. I am 54, female, postmenopausal. I had bariatric surgery 15.5 yrs ago at age 38 yrs, & my weight dropped to as low as 146lbs post op. The last 7 yrs however, my weight has fluctuated from between 160 to around 189lbs due to hypo, desk job, no exercise, high stress and poor food choices/portion control.

    I’ve been on levothyroxine for at least the last 7 yrs, starting at 25mcg. However, within the last 4 yrs my endocrinologist has gradually increased my dose to 50, 75, 88 and most recently to 100. My plasma TSH levels were being checked bi-annually whenever there was an increase in dose, but with my bariatric surgery, I have malabsorption issues and don’t always get all that I ingest by mouth.

    The side effects of the hypothyroidism were brutal & disabling the last 3 yrs [chronic unrelenting fatigue, joint pains, migraines, fullness & pressure in my ears, poor sleep, foggy brain/unable to focus, memory lapses, dry cracking & bleeding skin, hair loss, anxiety attacks & depression, etc].

    Now after 3 weeks on 100mcg, and my efforts to eat a primarily plant-based high protein diet (all cooked at home), I’ve recently lost 8-10 lbs (I have 2 bathroom scales and they don’t agree). I attribute this to the levothyroxine increase, primarily because I am serving my husband the same diet (he is on a steady dose of levothyroxine 75), and he exercises, but he hasn’t lost any weight at all.

    Three weeks ago when my dose was increased to 100mcg I did experience an obvious lack of appetite, fullness after eating very little, & an aversion to caloric-dense foods. I fear when I return for my 6-week blood draw after going to 100mcg, that the Dr. will suggest the weight loss is too much and move my dose back down. Truthfully, after 3 weeks I am on the mend, but not yet myself.

  7. I started on 50mcg in summer 2016. I then had surgery in September where I could not work out for 6 weeks. During that time I had used an app to keep track of my food and ended up losing 5 lbs in 3 weeks. Over the course of 6 months I dropped from 219 to 180 and have held that for a long time and then it went back up again. I only used the app and stayed within my calorie intake and worked out 2-3 times a week. I believe the loss was a direct result of being put on levothyroxine.

  8. This is a success story: I am a healthy, active 73 year old woman. During my late 60’s, I began a slow and progressive weight gain, from 145 to 165 pounds. Upon changing to a new doctor, I was diagnosed with hypothyroidism and began taking 50 mcg of levothyroxine daily. During the following several months, I began to feel more energetic, to have quicker mental clarity, and lost 10 pounds.

    Strangely, I have never been a big eater, and have always been a “picky”. Now, while taking levothyroxine, I find I am even less interested in eating (although I do maintain a fairly well-balanced diet). So, overeating was not the culprit. To sum this all up, my doctor continues prescribing 50 mcg, as my ongoing regimen. He required blood-testing every 4 months.

    If anyone is feeling concerned about losing weight, please advocate for yourself and be certain that your doctor runs regular blood-testing… AND TAKES YOUR INFORMATION SERIOUSLY. Best to all, Sherryl V.

  9. Hi, I have been taking levothyroxine for almost 2 years now and within the last 7 months I have noticed that I cannot gain weight and have lost about 5 lbs which for me is horrible because I am very thin (always have been) to begin with. I cannot afford to lose. I am slowly going to take myself off this which I told my Dr. and I am going to see an endocrinologist soon. I am 69 yrs old and was “never” told I had hypothyroid problem and was feeling fine until I started taking the levothyroxine. My question is why didn’t the Dr. see that this was the reason for losing weight?

    • Casey – It sounds like your levels are too high. Have you had a blood test to check it? The Dr. will probably just reduce your dosage a little and then after a few weeks you’ll have a blood test to see if you’re in the right range. It’s not too uncommon to have to adjust the dosage every once in a while.

  10. I am 55 years old, and have been on Synthroid for over 30 years. Prior to entering menopause, I controlled my weight through exercise and eating healthy, despite having a sweet tooth. In the past 7 years, I have been struggling to control my weight, have gained 15 pounds, and am having a lot of trouble losing it. I exercise daily, sometimes twice daily, eat around 1300-1400 calories per day with at least 80g of protein per day, lots of veggies and fruits, low on the sweets.

    In the past 6 months, my TSH levels changed by over 4 points, from being in the low numbers of normal to now being high, over the limit. Not sure what is going on, but my Dr. increased my dosage and I am hopeful that I will see some effective weight loss. It’s only been two weeks, and I don’t expect to see any changes for some time as I have been on the med for so long.

  11. I am 70 and discovered I have Hashimoto Hypothyroidism at approximately age 65. Started out at 25 mg and now at 88mg. I have been trying to lose weight for months. I cut back on what I eat and walk 2 1/2 miles a day and cannot lose any weight and exercise.

    After I retired at age 60 I weighed 175 lbs and lost 50 lbs but know that was due to me sitting at a desk all day. I have weighed 155 lbs for 5 yrs and cannot even lose a lb. So frustrated!!

  12. I was diagnosed with hypo after I have my daughter when I was 41. They started me on 25mg and then increased it to 50 and then 75. I just went for a physical and they said I was below the normal range and they increased it to 88mg. I have always been around 105 lbs and am 5’2″.

    Now my weight fluctuates between 98 and 102. I am concerned that I will lose more weight with the increase in my dosage.

  13. I had a thyroidectomy two years ago. I was started on 150 of Levoxyl and have gone to NDT and back. My weight increased when on a dose lower than 150 and my TSH is zero yet FT4 is high, yet I feel extremely hypo when on a reduced amount.

  14. I was diagnosed with Hyperthyroidism 1 year ago and did the RAI Treatment in January this year. I was put on the Levothyroxine in March. I have steadily gained almost 70lbs in less than 2 years. I have been taking Levothyroxine 150 and have still been gaining weight despite sensible eating and exercise. Now I am borderline diabetic so I am also taking Metformin 1000 per day. I also have PCOS so I am on birth control pills. I am not sure what else to do to lose this weight.

  15. I had a total thyroidectomy in February after being diagnosed with thyroid cancer, I can gratefully say that my 6 month scan came out clean and I am cancer free. However I am miserable, gained 27 lbs in 6 months and feel so tired all the time. I am also 54 years old and know some of that could be premenopausal.

    My endo slowly increased my synthroid levels throughout the year, I am now at 200mcg. I even got a second opinion from an Endo at Mayo and when I asked him what are the chances I will lose this weight. He said highly unlikely. I am taking all kind of supplements. Willing to try anything at this point to get my metabolism back.

    I eat right and am very active. I am frustrated and when I tell my doctors about my frustration, their only response is it’s normal. Are there any safe supplements I can take that will increase the positive effects of weight loss from taking synthroid that I read in this article?

  16. I was diagnosed with hypothyroid over 12 years ago, and stupidly stopped taking medication for it over 10 years ago. 5 weeks ago I started back on it, 100mcg, and have lost approx. 25 pounds in 5 weeks. My energy level has skyrocketed and my appetite is way decreased. I was also experiencing major fatigue and joint pain all over, which has greatly subsided. I will never stop taking synthroid again!

    • Mike, Few and far in between do I see other men commenting on these forums (which makes some sense considering the condition effects more females than males), but if you don’t mind me asking a personal question: we discovered my hypothyroidism about a year ago – though according to my GP who noticed the numbers being off in my blood work, it may have been the root of improperly diagnosed conditions since my early 20’s (now 29).

      I tried using natural supplements for a long time as well as changing eating habits etc, but eventually after minor weight loss, I was stuck due to the lethargy. Now, in my teens – present I’ve had a low libido, which my doctor told me can be caused by hypothyroidism and for some, helped by synthroid – I start at 50mcg tomorrow. Did you notice any increase in libido from the medication? No need to answer if too personal, but if other men wish to speak from experience, that’s appreciated as well! Thanks to all of you!

      • I am in my 40’s but had become tired all the time, foggy gained 30 lbs. in 3 years, and up to a month ago noticed my libido reduced majorly, I never had issues with erections but it became difficult to get one. My naturopath told me to get checked out, my TSH was at 12. I have been on synthroid for 2 weeks and I have lost 5 lbs, am sleeping better, have more energy, not foggy anymore, and no longer have erectile issues, thank goodness!

    • Same is the case with me.. I was diagnosed with hypothyroidism 5 years a go. That time I started thyroxine and lost 23 KGs weight in less than two months.. Then I got my TSH level test and it was back to normal..

      The rubbish I did, I stopped taking medicine. And now I weigh 99 KGs and my TSH level is 16.7 where it should be 4.5. I’m now prescribed Levothyroxine it’s been 4 days I’ve started taking it.. I wish I lose weight soon..

      It’s a kind request if someone can suggest me any other medicine that could help me lose fat, please tell, I’ll use it with consultation of my medical specialist!!

  17. I went to an integrative medicine Dr for migraines that weren’t going away with regular treatment. He started me on a lot of vitamins and I met with a nutritionist so I began eating healthier. And although I am not clinically hypothyroid I was exhibiting signs of hypo (decrease energy, weight gain, brain fog) he started me on levothyroxine.

    Last year I just kept gaining weight up to about 210lbs. I was down to about 182lbs when I first saw him 7 months ago and as of today I am at 150lbs. I’m happy with the weight loss but would like to know when it will stop. I’m sure the medicine is a large factor but the lifestyle changes, I believe, are a contributing factor as well.

  18. I really appreciated the thorough and balanced look at Synthroid in this article. I initially had a great response to a low dose of Synthroid (started at 12.5 micrograms). Within 24 hours I had more energy and my hot flashes (I’m 55, in menopause) were almost completely gone. Now, at 100 micrograms, I’m seeing a return of hot flashes (not to the pre-Synthroid level but still worse than six months ago when I started the drug), and my energy isn’t quite what it was.

    I initially saw a little boost in my libido at the start of taking Synthroid, but that disappeared after a month or so. My joint pain comes and goes, but I also have arthritis and maybe fibro, so I don’t think that symptom is totally due to hypothyroidism. I don’t believe I lost any weight on Synthroid (no scale, but I have pants LOL, had gained 20+ pounds in the last two years–menopause + thyroid disorder + stress + need knee replacement = oh, the horror).

    I felt like I was ready to lose weight, via more exercise and slight adjustments to my diet, but then my energy dipped again. I have felt slightly fewer cravings for carbohydrates and more cravings for protein lately, although I still can’t give up carbs (gun to my head = no). I’m not sure if I should go up on my dose, so will have to have a consult. I do think I get some food effect or medication effect, as I have a hard time taking Synthroid on its own, without any other medications, on a completely empty stomach.

    I’m trying to find information about how much the dose should be adjusted for food effect (I worked in pharma, so I know the data are out there somewhere), but I can’t find it. Meanwhile, I’m tinkering on my own until I see a doc, adding 50 micrograms every other day (I live in a country where I can get Synthroid without a script). I do see an increase in my energy and reduction in my joint pain when I do that, but I also get some occasional racing heart rates and skipped beats (was also an EKG tech, so I know not to push this).

    To compound the matter, I changed to a stronger brew of coffee (crazy work deadlines), so that could account for the cardiac symptoms. And I still don’t know if there are adrenal issues that need to be dealt with, or if adding some T3 might be better than constantly uptitrating and downtitrating my Synthroid dose. Frustrated and ready to figure this out, but not confident I will and even less confident in the medical establishment to do so.

  19. I have been on synthroid meds since I was 28 years old am now 71. Up until about a year and a half ago I pretty much stayed on a dose for a longer period of time All of a sudden my thyroid is making me lose weight. I have been seeing a naturopath and also a thyroid doctor. Each has a different view on what dosage I should be on… Was on 75mcg up until my last blood test 9 days ago am now taking 50mcg for 3 days and 75 mcg for 4 days… I have increased my protein, eating more often, exercising. When I look at myself all I want to do is cry. I weigh 115 right now and am 5’6″.

  20. I am 51 years old and am 5’5″, I have 6 children and work full time and was/am a marathon runner. My weight was always around 120 ish and I always craved a lot of sugar. When I finally was diagnosed with hypothyroidism, while it made sense that I was tired a lot (!), it made so much more sense why.

    I started taking 25 mcg synthroid and gradually have increased to 75 where I have been for the last year and a half, my weight has dropped to 110-112 lbs. This feels and seems reasonable for my activity level but I do feel a lot better. I think the weight loss is directly connected to the adjustment in my BMR, as I have always been a healthy eater and exerciser.

  21. I was at ~125 lbs before the onset of my hypothyroidism. I slowly started losing weight – down to 120, then 117, then 115 and finally 112 lbs, and knew something was up with me. Since my diagnosis of a TSH level of 6.9 and being prescribed 50 mcg of Synthroid this past April – I have lost another 2 lbs. I am now at 110 and my height is 5’6.

    My family, friends and strangers all think I am suffering from an eating disorder – when I really scarf down giant plates of food on a daily basis!!! I am scheduled for another visit soon with the doc, to see if perhaps I am overmedicated and now exhibiting hyperthyroid systems (other side effects I am having include heart palpitations, chest pain, and anxiety & OCD like thoughts/symptoms.) We’ll see how it all plays out, but I would say the weight loss is definitely unwanted. :(

    On the other hand – my brain fog has completely cleared up, my energy levels are back, and the Synthroid has given me some really vivid lucid dreams which can be cool. :)

    • Hi, I am going through the exact same thing. I am so concerned about how much weight I’m losing and now my doctor increased my synthroid amount. Have you gone back to your doctor yet? Is it possible to go from a “hypo” to “hyper” thyroid? I really don’t want to lose any more weight, I’m starting to look to sickly skinny. Thank you, Sarah :)

  22. I have been on synthroid for 1 month and it is the only medication I take. I was at 280lbs when I started. I weighed myself this morning and am at 254lbs. I have not changed my routine or eating habits at all. I take .25 mcg a day. I am only 37 years old so yes I have lost a significant amount of weight and just visiting my doc yesterday she is increasing to .50 as my levels have not come down.

    • Have you had any more weight loss since May? I am also 37, and have had a thyroid level hovering just barely in the low normal range for the past 15 years. Finally it dropped low enough that they started me on meds .25mcg as well. Just started last week and have high hopes. I’ve exercised like a mad woman in the past (2-5 miles running daily, 1-2 miles walking daily, 1-2 hours of classes at the gym 5 days a week, 45 minutes on the weights daily… yes, I’m serious and not exaggerating).

      I also ate STRICTLY. Was smaller than I am now, but still had fat rolls to spare. Am praying this is the boost I need to get back on track with that (I quit because it was too much work for too little reward!)


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