≡ Menu

Too Much Synthroid (Levothyroxine) Symptoms

Synthroid (Levothyroxine) is a synthetic form of T4 (thyroxine), a hormone secreted by the follicular cells of the thyroid gland.  Individuals with insufficient levels of thyroxine (T4) exhibit symptoms of hypothyroidism such as: depression, lethargy, malaise, and sleepiness.  Regular administration of synthroid (levothyroxine) is thought to reverse symptoms of hypothyroidism and normalize all neurophysiological processes impaired by low thyroxine (T4).

When initiating treatment, certain patients may run the risk of taking too much synthroid.  In a majority of cases, individuals that take too much synthroid do so unintentionally.  It is common for patients to misinterpret dosing instructions given by a medical professional and/or pharmacist and mistakenly ingest larger than instructed doses.

In other cases, a doctor may inadvertently prescribe too high of a synthroid dosage for a particular patient.  Since synthroid has a narrow therapeutic index (NTI) for dosing, even slightly too much of the synthetic hormone may provoke a tailspin of unwanted symptoms, most of which resemble hyperthyroidism (or excess thyroid hormone).  If you are taking synthroid and suspect that you may have ingested an excessive amount, it is important to beware of severe synthroid side effects and adverse reactions.

Too Much Synthroid (Levothyroxine) Symptoms

Below is a list of possible symptoms that you may experience if you took too much synthroid (levothyroxine).  Understand that the number and severity of your symptoms will likely be contingent upon how much more synthroid you took than was necessary.  For example, if you were prescribed 100 mcg per day, yet took 300 mcg – you’ll likely exhibit more noticeable effects from too much synthroid compared to someone who was prescribed 25 mcg and took 50 mcg; the contrast is more significant in the first example.

Since synthroid is a synthetic version of thyroxine (T4) that serves as a non-bioidentical replacement, excessive amounts may lead to hyperthyroidism-like symptoms.  Common symptoms experienced from those who take too much synthroid include: anxiety, diarrhea, rapid heartbeat, sweating, and increased body temperature.  Should you experience any of these symptoms while taking synthroid, medical attention is warranted.

  • Anxiety: There is a relationship between excessive thyroid hormone and neuropsychiatric anxiety. If after taking synthroid you feel insanely anxious, jittery, and nervous – it could be a result of an abnormally high dosage.  Some users have reported that taking too much synthroid leads to so much anxiety that they cannot sleep, think clearly, or interact socially with others.  Additionally, anxiety resulting from excess levothyroxine may provoke panic attacks or unpredictable feelings of panic and fear.
  • Bone density decrease: There is evidence to suggest that too much synthroid replacement can accelerate bone loss, which in turn may increase likelihood of fractures. Decreased bone density is most likely to occur among those that have taken too much synthroid over a prolonged duration.  Administration of a single supratherapeutic synthroid dosage is unlikely to prompt significant bone loss.  Decreased bone density may be most noticeable among older adults and elderly synthroid users, but may occur in all ages if an abnormally high dosage is repeatedly administered.
  • Chest pain: If you’re experiencing chest pain from synthroid treatment, it is recommended to immediately seek medical evaluation. Chest pain may be a sign of an adverse cardiac response to the medication.  Since high doses of synthroid can affect heart rhythms and function, it is important to rule out serious complications associated with treatment.  Usually chest pain is most common among those that ingested significantly more synthroid than necessary.  Chest pain may also be interrelated to the physiological anxiety and tension associated with high doses.
  • Diarrhea: It is known that excessive levothyroxine (synthroid) can cause severe gastrointestinal distress and stomach aches. Many people lose weight from high doses simply because they cannot hold down food.  Too much synthroid is thought to expedite the movement of food through the digestive tract, leading to frequent bowel movements or diarrhea.  Diarrhea can occur even at standard doses, but is more likely to occur (and be more severe) among high-dose synthroid users.
  • Difficulty concentrating: Ingesting excess synthroid (levothyroxine) is likely to cause difficulties with concentration and focus. You may feel so anxious, jittery, and wired with disconcerting physical symptoms – that it becomes nearly impossible to stay focused on any cognitively demanding task.  To ensure that your concentrative abilities return, you’ll want to get your dosage adjusted and/or refrain from using unnecessarily large synthroid doses.
  • Fever: Thyroid hormones play an important role in thermoregulation and when modified to extremes (as in the case of taking too much synthroid), body temperature can fluctuate. In the event that you took too much synthroid, you’re likely to feel excessively hot and with a fever.  If the amount ingested wasn’t considerably more than your daily requirements, the fever may be low-grade.  However, in the event of an overdose (or ingesting significantly more than necessary), the fever is likely to be high and possibly fatal.
  • Hair loss: Individuals taking too much synthroid are more likely to experience hair loss than those taking proper dosages. While hair loss can occur as a side effect during the first few months of treatment, most users notice that hair loss subsides as the body adapts to the daily synthroid administration.  If you’ve been regularly ingesting too much synthetic thyroxine (synthroid), hair loss may be more substantial and may never subside until the dosage is reduced.
  • Headaches: Another common symptom associated with ingesting too much synthroid is headaches. While headaches are a normal side effect of the medication (even at standard doses), excessively high doses of synthroid trigger severe headaches (e.g. migraines).  If you feel a throbbing, incessant headache that won’t subside, it could be a sign that you’ve administered too much synthroid.
  • High blood pressure: Synthroid treatment may trigger hypertension, especially when too high of a dose is ingested. Blood pressure spikes and/or irregularities may be most prominent among those who have a history of hypertension, but can occur among any user that has unintentionally (or intentionally) administered too much synthroid.  It is important to realize that if ignored, hypertension (from too much synthroid) could lead to complications such as: blood vessel damage, heart attack, and/or stroke.
  • Hot flashes: Taking too much synthroid can cause hot flashes or sudden waves of feverish heat, usually localized in the facial region. The hot flashes may be accompanied by profuse sweating, and in some cases, an actual fever.  Even slightly too much synthroid may be enough to trigger more hot flashes than usual.  That said, hot flashes are also considered a normal side effect of synthroid, so don’t automatically suspect that you took too much if you only experience a hot flash.
  • Insomnia: Individuals that regularly ingest supratherapeutic doses of synthroid are likely to exhibit insomnia or inability to fall asleep (or stay asleep). Those that inadvertently ingest too much synthroid will likely notice that no matter how hard they try to relax and drift off to sleep – they cannot overcome the insomnia.  While mild insomnia may not be too problematic, sometimes it leads to a full night of sleeplessness – which can have numerous deleterious health implications.
  • Irritability: The combination of anxiety, jitteriness, and nerves can lead some individuals that took too much synthroid to feel irritable. You may find yourself angry at every “little thing” and as if you’re ready to snap at friends and/or family over minor disputes.  It is important to recognize that if you weren’t irritable prior to taking synthroid, it’s probably induced by the medication.  Though this is a side effect experienced by many individuals taking standard doses, it is especially common among those who took too much.
  • Menstrual irregularities: Female users that take too much synthroid are likely to experience menstrual irregularities. Some women report that after starting synthroid, their periods are whacky and completely unpredictable – this is a normal side effect.  However, chronically taking too high of a synthroid dosage may cause abnormally light periods and/or even missed periods.  Assuming you’ve been taking unnecessarily high synthroid doses for awhile, time between periods is likely to be prolonged.
  • Muscle weakness: It’s no surprise that individuals who take too much synthroid could end up with serious muscle weakness. High concentrations of levothyroxine can accelerate bone density loss and possibly even muscle loss via increases in BMR.  The reduction in bone density and muscle tissue may be responsible for causing muscle weakness.  Muscle weakness may be most noticeable among older adults and/or elderly synthroid patients.
  • Nervousness: Nervousness can occur as a standard synthroid side effect – even when taken at the proper dose. That said, if you end up taking too much synthroid, nervousness is very likely to occur – leading you to feel uncomfortable and riddled with anxiety.  The nervousness may be accompanied by a racing heart, sweating, thoughts of panic, and muscle tension.  Once your dosage is readjusted to a proper level, nervousness should lessen in severity.
  • Profuse sweating: Taking slightly more synthroid than necessary can increase likelihood of sweating. On the other hand, taking substantially more synthroid than necessary is nearly a surefire guarantee to sweat profusely.  Although sweating is a standard side effect reported at normal doses, profuse and/or excessive unremitting sweats are most likely to be a result of excess levothyroxine intake.  Too much synthroid increases body temperature, causes hot flashes, and alters blood flow – ultimately causing some users to sweat uncontrollably.
  • Rapid or irregular heartbeat: A very common symptom of taking too much synthroid is rapid or irregular heartbeat. Most individuals are consciously aware of changes in heartbeat and/or rhythms as provoked by synthroid.  Ingesting too much levothyroxine can cause atrial fibrillation or even heart failure (especially among those with preexisting heart disease).  The greater the quantity of synthroid ingested over the optimal amount (for you as an individual), the more likely you are to experience heartbeat irregularities.  If you took too much synthroid and are experiencing heartbeat irregularities, immediate medical attention is essential.
  • Shortness of breath: If you took too high of a synthroid dosage, you may feel as if you’re constantly gasping for air or having a tough time breathing. Shortness of breath is common among those who take too much synthroid.  While shortness of breath could just be a result of increased anxiety from too much synthroid, it could also be a sign of a more serious adverse reaction (e.g. heart attack).  For this reason, it is necessary to seek medical evaluation if you have this symptom after taking too large of a synthroid dose.
  • Sleeplessness: If you took more synthroid than prescribed (or too much for your particular condition), you may be unable to sleep at night. While insomnia may occur among those that took slightly more synthroid than necessary, outright sleeplessness is common among individuals that ingested considerably larger doses than medically required.  Someone that overdoses on synthroid will have a difficult time getting any sleep – and if they do get sleep, the quality will be poor.
  • Temperature sensitivity: You may find that warm temperatures are intolerable after taking too much synthroid. This is because excess levothyroxine increases blood flow to the skin, making you feel warmer than usual.  It also generates more body heat than necessary as a result of changes in metabolism.  As a result, you sweat more, feel feverish, and may be unable to tolerate a warm or hot environment.  Upon correction of your synthroid dosing, you may feel as if you can actually tolerate a warm environment.
  • Tremors: Abnormally high doses of synthroid can cause some individuals to shake uncontrollably, particularly in the hands. If you’ve noticed tremors in your hands, legs, facial muscles, etc. – it could be that you’re overstimulated with too much levothyroxine.  A doctor may need to readjust your dosage if the tremors continue throughout your treatment.
  • Vomiting: A telltale symptom that you may have taken too much synthroid is vomiting. Prior to vomiting you may feel extremely nauseous and unable to maintain an appetite.  Although not everyone who takes too much synthroid will vomit, if you’re vomiting, it is likely a sign from your body that too much has been ingested and/or you’re unable to tolerate the drug.  If you constantly vomit and feel like you have the flu, seek medical attention immediately.
  • Weight loss: When initially beginning synthroid treatment, it is common for users to end up losing some weight; this is due to a reversal of hypothyroidism-induced BMR slowing. If you’ve been taking too much synthroid, not only will you likely feel like an anxious, sleepless maniac, but you’ll probably shed more body weight than expected.  Some of this weight loss will be a result of GI changes (e.g. diarrhea), some may be due to decreased bone density and/or muscle loss, and most will be from an abnormally increased BMR (basal metabolic rate).  (Read: Synthroid and Weight Loss).

Note: Not all people that take too much synthroid will experience every last symptom listed above.  Symptoms of taking excess synthroid may be subject to interindividual variation.  If you believe you took too much synthroid and are experiencing any symptoms, consulting a medical professional is advised.

Taking Too Much Synthroid: Interindivdiual Variation in Dosing

Individuals undergoing treatment for hypothyroidism with synthroid are prescribed dosages aimed to optimize TSH (thyroid stimulating hormone) levels.  Excessively high TSH levels signifies that an individual is likely not getting enough synthroid.  Since the severity of hypothyroidism is subject to individual variation and synthroid dosages necessitate patient-specific optimization, “too much synthroid” for one user may be a normal dose for another.

A person with severe hypothyroidism who weighs 200 lbs may take around 1.7 mcg/kg/day – for a daily total dosage of ~154.22 mcg.  Should the individual end up taking 175 mcg per day, he/she may exhibit subtle symptoms associated with too much synthroid.  On the other hand, someone who weighs 140 lbs and is taking 1 mcg/kg/day for subclinical hypothyroidism, a total daily dosage may be just 63.5 mcg.

If the individual instructed to take 63.5 mcg of synthroid ends up taking 175 mcg per day, more severe symptoms are likely to emerge because the recommended dosage will have been surpassed by a significant amount.  The lesser the extent to which an optimally calibrated dosage is surpassed, the less severe and/or numerous the symptoms of too much synthroid are likely to be.  The greater the dosage over the optimal amount of synthroid needed for optimal function, the greater the symptomatic severity associated with the “overdose.”

Reasons patients may take too much synthroid

There are several hypothetical reasons as why a patient may end up taking too much synthroid.  While taking too much is certainly not the “norm,” it could be a result of: misinterpreted dosing instructions, improper dosage (as prescribed by a doctor), or intentionally taking more than usual (either to improve symptoms or to inflict self-harm).  Most individuals that take too much synthroid do so unintentionally and/or unknowingly.

  1. Misinterpretation of dosing instructions: Some synthroid users may misinterpret dosing instructions as given by their doctor. While dosing instructions are generally confirmed with a pharmacist prior to administration of synthroid, some individuals are more absent-minded than others. It is possible to consider that a simple slip-up on the end of the patient may lead to ingestion of a dose that is larger than necessary.
  2. Improperly calibrated dose: Although most doctors attempt to prescribe patients with a minimal effective dose of synthroid, not all patients respond to low doses when beginning treatment. For this reason, a doctor may slightly overshoot the necessary dosing needs for a particular patient. Regular administration of an improperly calibrated dose can provoke symptoms of too much synthroid.
  3. Faster symptomatic relief: In rare cases, a patient may try to play “doctor” on themselves by making personal adjustments to their dosing. A patient may experiment with higher-than-necessary dosages in attempt to reverse hypothyroidism symptoms as soon as possible. Although the patient may believe that he/she will attain faster relief by taking a greater dosage than prescribed, this may lead to adverse effects and complications associated with too much levothyroxine.
  4. Intentional overdose: Another small percentage of patients may feel anxious, depressed, and possibly suicidal while taking synthroid. These individuals often have an underlying comorbid neuropsychiatric diagnosis (e.g. major depressive disorder, bipolar disorder, etc.). It is possible that the patient may attempt to inflict self-harm by overdosing on synthroid (levothyroxine).  In the event of an overdose, very severe symptoms are likely to arise – requiring immediate medical attention.

What should you do if you took too much synthroid?

If you know (or suspect) that you may have ingested too much synthroid, seeking emergency medical attention is necessary.  Complications arising from a synthroid overdose could be fatal if they aren’t addressed in a timely manner.  Thereafter, you should take steps to minimize the likelihood of future dosing errors by reviewing and confirming dosing instructions with your doctor.

  1. Seek medical attention: Since taking too much synthroid could prove to be fatal, it is necessary to seek medical assistance as soon as possible after your dosing. If you know that you overdosed and/or intentionally took too much, call emergency medical services and/or get yourself to a hospital. In rare cases, individuals may die of hyperthermia and/or cardiac arrest associated with elevated levothyroxine concentrations.
  2. Refrain from synthroid usage: If you know you took too much synthroid, your doctor may instruct you to refrain from synthroid usage for a day or two after your abnormally high dose. Don’t immediately stop taking synthroid without medical instruction, but be cognizant that in the event of an overdose, ingestion of additional synthroid may exacerbate adverse effects. Work with your doctor to determine when it is safe to resume normative synthroid administration.
  3. Optimize future dosing: Sometimes you may need to work with your doctor to review your current dosing regimen. This may involve blood testing for TSH, FT4, and FT3 to determine how you are affected by the synthroid. Assuming concentrations of TSH aren’t within a normal range (e.g. are too low), you may need to reduce your synthroid dose.  The goal should be to take a minimal effective dose of synthroid – or just enough to optimize TSH levels without inducing side effects from too much levothyroxine.

Have you ever taken too much synthroid (levothyroxine)?

If you’ve ever taken too much synthroid, leave a comment detailing your experience.  Share the symptoms you experienced, how much synthroid you took, and whether taking too much was accidental or intentional.  If the dosing error was unintentional, did it result from misinterpreting in the dosing instructions as given by a doctor or your pharmacist?

For those who intentionally took a higher-than-prescribed dose of synthroid, share your motive for doing so.  Document the most prominent symptoms you experienced as a result of ingesting excess levothyroxine.  How long did it take you to get over these symptoms and did you discuss them with a medical professional?

Related Posts:

{ 16 comments… add one }
  • Laura June 7, 2016, 11:05 pm

    I have been over medicated on thyroid hormone. It is definitely not comfortable. I feel sick, dizzy, sharp headache, anxious, impaired cognition, and all the symptoms mentioned in above article. Symptoms will subside at lowering the dose. It takes about a week to feel a difference, not completely better.

    That takes a good 8 weeks. But if still feeling hyper at 10 weeks, another decrease may be in order. I just recently got a super potent dose of Synthroid 100 mcg. and developed hyper symptoms after taking only 8 days of pills. Not a happy camper. Hope this helps someone.

    • Nancy July 9, 2016, 5:26 pm

      I too was over medicated, just recently went down to 112mg from 200mg. Switched endocrinologist and that’s where the problem was found. I had been dealing with high anxiety, sleepless nights, night sweats and rapid heartbeat… I have to go back in 3 months to see where I stand. Dr doesn’t think I should have labs in a month because 3 months would be a more accurate way to determine.

      I’m hoping like everyone says I’ll feel some side edits subside within 2 weeks but I know I won’t be completely side effect free til I am on the right dosage. I have congenital hypothyroidism (born without thyroid gland).

    • Laura L Powers September 6, 2016, 9:08 pm

      I have been overmedicated accidentally for a while. I have had a hard time getting my dosage right. Do the symptoms of heart disease go away once you have gotten the right dosage? I have been on high dosage for awhile. Does anyone know if there is permanent damage?

  • Cathy June 12, 2016, 1:25 pm

    I had been taking 75mcg one day 100mcg the next. My GP said I needed to increase my dosage to 100 a day. This happened months back. I have reduced it back to 75 now as I was living in a permanent state of being awake. If I slept it would be for about an hour to 90 mins and was ratty and irritable.

    I was also worrying about my work for no apparent reason. After routine tests my GP said to reduce my meds and only have the higher dose on two days a week. Well, today I realized… I’ve started sleeping again.

  • Raven June 25, 2016, 10:18 pm

    I was prescribed 200 mcg. I was so upset I couldn’t loose weight because of this condition and unstable levels I increase my own dosage by take 800 mcg. That night I had horrible leg cramps that hurt for two weeks and I never did that again. I was stupid.

  • Nancy July 4, 2016, 3:23 pm

    I was over medicated by my Dr. I knew these last 2 yrs I wasn’t feeling right. I brought to her attention we did labs and I was always told too high she said or low at times. But never did my dosage change just a day cut out or half of my pill on a Sunday instead of whole. I experienced of the symptoms and even worry that this long on a high dosage could have hurt my heart.

    I’ve had 2 ekgs done and both normal. I recently was told I was given too much meds after a new endocrinologist told me I was on a high dosage for my weight. 200mg at 130lbs. Now I am at 120lbs from loss of weight that happened within 3 weeks. I feel my body just went through a crash and said I can’t keep up no more.

    Right now I’m at 150 mg until my next labs, guessing my Dr is cutting it down little by little til we get to the right dosage. I hope these symptoms go away, and I get back on my old self.

  • Cindy August 5, 2016, 9:35 am

    I purposely took 150mcg instead of 50mcg because I felt I needed that extra jump to get me thru some days… side effects of that are throbbing headaches, excessive body heat, and insomnia so far…

  • Julie August 10, 2016, 4:41 am

    I have been on 0.5 mcg of synthroid for a while and was fine. But I started exercising a lot more,ingesting coconut oil and taking vitamins. I then began having these horrible, horrible bouts of panic, flushing, shaking, shortness of breath and nausea. One time I even threw up. When I realized it could be the synthroid, I quit taking it for a whole week to let me body calm down. Now I only take half – 0.25 mcg. I would not wish these symptoms on anyone! I probably should have gone to the hospital because it was that bad.

  • Nancy Lazenby August 20, 2016, 6:50 pm

    I am prescribed 100 mcg per day. This morning I accidentally took tomorrow’s dose, forgetting that I had already taken my pill. Frankly, I don’t feel any different 4 hours later. I am always depressed, in spite of taking Prozac and Trazodone along with .25 Xanax daily, and I sleep whenever I want to. I live in the deep south and no AC in the world can keep up with our heat, therefore if I am sweating I hardly notice it.

    It scared me when I discovered that I took two days worth of synthroid in one day, but otherwise I don’t notice side effects. Should I go to ER? Only option here in my town. I am caregiver for Alz husband and don’t want to get out needlessly, but this website has me worried that I might have a cardiac event!

  • Ann September 3, 2016, 10:09 am

    About 7 years ago I had thyroid cancer and had my thyroid completely removed. Afterward I stayed cold all the time, so cold I had a blanket year around. I was taking over 200 mg a day at first because of my weight. I was at 250 pounds. Anyway about 2 or 3 years ago I had gastric sleeve surgery and lost about 50 pounds. The doctor decreased my synthroid to 137 mg a day except on Sunday and then I take 2 of my pills making it 274 mg.

    I have started having nearly all the symptoms above just this year. Hot flashes are horrible, nearly every morning I wake up sweating even with the air on a low temp. I have had rapid heartbeat, can’t sleep more than 4 hours at night and my head bothers me all the time.

  • Linda Dinnage September 15, 2016, 7:04 pm

    I have been on synthroid for 30 years and suddenly after intentional weight loss I began to be overdosed on my thyroid medication. I was reduced from .112 to .100 and my over medication only changed slightly. My doctor has reduced it to .05, cut it by half. I hope this works.

    We think I was over medicated for quite a while. I had headaches, jittery feelings, and palpitations, luckily no hyper tension, my blood pressure is very,low on the best day. I hope this will settle. Is it likely I might come off the medication or can it go lower?

  • Kathy L. September 27, 2016, 4:04 pm

    I quit smoking. Most people who quit need more thyroid meds but I went hyper. Hyper symptoms is not good anytime but especially when you just quit smoking. What a nightmare but I survived and now I am a non-smoker and need less levoxyl.

  • Bob October 5, 2016, 12:19 am

    I’m a male in my late 50’s taking 100 mcg of Levothyroxine daily. I felt some jet lag after a 12 hour flight and decided to take an additional 88 mcg to see if it would make me feel better. Big mistake. That night I got zero sleep. The next night 1 hour. I haven’t taken any additional these past 2 days and I’m hoping tonight I get back to normal.

  • SANDRA October 10, 2016, 6:11 pm

    I am really worried about my daughter. She has been on Levothroxine (50ml) for years. About three weeks ago annual blood tests indicated that she needed an increased dose (75ml) Within a weeks she was displaying many of the symptoms above. She has Down Syndrome, and is unable to vocalize her distress. Her behavior and anxiety is resulting in her becoming aggressive. Whilst we are awaiting her to consent to blood tests she remains on 75ml. No one seems able to take my concerns seriously, putting it down to her having Down Syndrome. I am at my wits end trying to get answers.

  • David C Mills October 12, 2016, 9:27 pm

    I had a thyroidectomy 2 years ago and have been on 150 micrograms of levothyroxine. Everything was fine until about 30 days ago. Had severe palpitations and visited the ER. My endo lowered my dose to 125. Felt awful for about a week but then began to improve. The palpations subsided and it looked like that 125 would work fine.

    Then I got hit with heavy anxiety out of the blue. He lowered it again to 112 last week. Had to get a prescription for Xanax in the meantime to control the adrenaline surges. I’m praying these begin to subside over the next week. Awful experience.

  • Heather October 13, 2016, 11:32 am

    I started on the low dosage and didn’t see any improvement so I asked if they could up it a little. Felt okay but now every time I don’t take it at the right time in the morning or forget altogether, I have a migraine that lasts all day, despite taking the pill eventually. Is this normal?

Leave a Comment