Are You Taking Too Much Thyroid Medication?

Thyroid hormone replacement drugs are used to treat hypothyroidism—a condition in which your thyroid does not produce enough thyroid hormones.

When you take the proper dose of these medications, they are considered safe and have few side effects. If you are taking too high a dose, however, you can experience unpleasant symptoms. This is known as overmedication.

This article discusses the causes and symptoms of overmedication with thyroid hormone replacement drugs.

symptoms of thyroid hormone replacement overmedication

Verywell / Katie K

Thyroid Hormone Replacement Drugs

Levothyroxine is a type of thyroid hormone replacement drug that is often used to treat hypothyroidism. Brand names for levothyroxine include Synthroid, Levoxyl, and Tirosint.

Natural dessicated thyroid (NDT) is also used to treat hypothyroidism. For some people, NDTs work better than levothyroxine, and many people prefer them because they are more natural. Brand name NDTs include Armour and Nature-Throid.

Usually, people begin thyroid hormone therapy with a low dose that is gradually increased. In part, this is because hypothyroidism progresses over time. But starting therapy with a low dose is also helpful for reducing the risk of overmedication.

Signs and Symptoms of Overmedication

Signs and symptoms of thyroid hormone overmedication can vary, but some common ones include:

  • Elevated pulse and blood pressure
  • Anxiety, nervous energy, tremors
  • Feeling irritable, overemotional, erratic, or depressed
  • Difficulty concentrating
  • Difficulty sleeping
  • Fatigue
  • Feeling overheated, even when others are cold
  • Diarrhea
  • Feeling like your heart is skipping a beat or racing
  • Weight loss with no change in your diet/exercise routine
  • Increase in food intake with no weight gain

In some cases, symptoms of overmedication can be similar to those of hypothyroidism. You may feel more exhausted than usual, or achy and as if you have the flu; you may put on weight, or feel jittery and anxious.

In fact, it's not unheard of for a person to visit their doctor to get tested, certain that they need an increased dosage, only to discover that their symptoms are actually due to overmedication.

Thyroid Disease Doctor Discussion Guide

Get our printable guide for your next doctor's appointment to help you ask the right questions.

Doctor Discussion Guide Old Woman

How Overmedication Occurs

There are a number of ways you can become overmedicated with your thyroid replacement drug. Sometimes, it takes trial and error to get your dosage just right. Prescribing mistakes can happen as well.

Dosage or Drug Quality Issues

Overmedication may occur when there is an error in dosage. For example:

  • Your doctor may prescribe a dosage that is too high for you.
  • Your pharmacist may give you the wrong dosage or incorrect instructions for use.

It is also possible that the quality of your medication may change from one refill of your prescription to another. This is sometimes the case when your medication is produced by several different manufacturers.

If you are taking generic levothyroxine, you may receive a batch of medication that is more or less potent than your previous refill. Even a slight change of potency from one refill to the next can lead to hypothyroidism.

Switching formulations of levothyroxine—for example, from tablet to gel-caps or liquid—can also cause overmedication. That's because your body absorbs certain formulations of levothyroxine better than others.

In particular, both Tirosint liquid gel-caps and Tirosint-SOL liquid levothyroxine absorb better than levothyroxine in tablet form. You may be prescribed gel-cap or liquid levothyroxine if you are allergic to dyes or fillers, but the switch may result in overmedication.

This is why close monitoring is important. You should get your TSH level checked within six weeks after beginning thyroid hormone replacement, or after changing the brand or dose of your medication. 

Pay particular attention to symptoms that develop after a recent pharmacy refill. They may be due to a medication error or change in the formulation.

Change in Diet

Changing your diet can affect how well your body absorbs thyroid hormone medication. For example, if you were eating a lot of fiber and then cut back on your intake, you may absorb higher levels of thyroid medication.

Supplements

Certain supplements can add to the effects of your thyroid replacement and lead to overmedication.

Pay close attention to supplements featuring the terms "thyroid support," "energy support," "thyroid glandulars," "adrenal glandulars," and "bovine glandulars." Some of these supplements contain thyroid hormone from animals.

Supplements that contain iodine, such as bladderwrack (Fucus vesiculosus), kelp, bugleweed, Irish moss, or seaweed are also culprits. Too much iodine, in particular, can over-stimulate your thyroid and trigger hyperthyroidism. 

Drugs that contain estrogens, such as hormone replacement medications and contraceptive pills, can interfere with thyroid hormone absorption. When you stop taking them, your thyroid medication may be absorbed better, causing you to become overmedicated.

Hashimoto's Disease

With Hashimoto's disease, your thyroid hormone levels can fluctuate rapidly. Hashitoxicosis refers to the phase when your thyroid is over-functioning and producing more thyroid hormone.

Taking your thyroid hormone replacement medication when your thyroid is in hashitoxicosis can temporarily cause hyperthyroidism.

Pregnancy

During pregnancy, your need for thyroid hormone increases, so you may need to be prescribed a higher dose of medication than usual.

Once you have the baby, your need for thyroid hormone drops. Hence, the dose of thyroid hormone replacement you were taking during pregnancy could be too high for the postpartum period. This can result in hyperthyroidism.

Monitoring for Overmedication

Doctors typically use your thyroid blood test results to see if you are getting too much medicine. In some cases, having a TSH level that is lower than normal or a T3 or T4 level that is higher than normal can be a sign of overmedication.

Summary

You may become overmedicated if the dosage or type of thyroid hormone replacement therapy you are taking changes. Certain health conditions and lifestyle changes can lead to overmedication, too.

Because the symptoms of overmedication can mimic hyperthyroidism or hypothyroidism, it's important to have your TSH levels checked regularly and any time your medication changes.

A Word From Verywell

Symptoms of being overmedicated with thyroid hormone replacement drugs are often uncomfortable, but rarely dangerous. Fortunately, eliminating thyroid-boosting supplements and/or cutting back on the dosage of the drug solves the problem.

Your doctor should run periodic thyroid tests and adjust your dosage as needed until your thyroid levels return to more normal, and your symptoms of overmedication are eliminated.

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