Are You Taking Too Much Thyroid Medication?

The standard thyroid hormone replacement drug used to treat hypothyroidism is levothyroxine (brand names include Synthroid, Levoxyl, and Tirosint). Other medications include a natural desiccated thyroid drug, such as Armour or Nature-throid, and liothyronine sodium (Cytomel). 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 and uncomfortable symptoms.

symptoms of thyroid hormone replacement overmedication
 Illustration by Katie K., Verywell

Signs and Symptoms of Overmedication

Signs and symptoms of 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 being overmedicated can, paradoxically, be similar to those when you are hypothyroid. You may feel more exhausted than usual, or achy and as if you have the flu; you may put on weight, despite feeling jittery and anxious.

In fact, it's not unheard of for a person to go to the doctor to get tested, certain that they require an increased dosage, only to discover that the symptoms they're experiencing are actually due to overmedication.

How Overmedication Occurs

There are a number of ways you can become overmedicated with your thyroid replacement drug. It can sometimes take trial and error to get your dosage just right, and prescribing mistakes can happen as well.

Dosage or Drug Quality Issues

The dosage of thyroid hormone replacement that your doctor prescribes may be too high for you. This is why close monitoring is important, which means getting your TSH checked within six weeks after beginning thyroid hormone replacement or after a dose or brand name change. 

If you've switched from a tablet form of levothyroxine to Tirosint liquid gel-caps, or Tirosint-SOL liquid levothyroxine—formulations of pure levothyroxine for people who are allergic to dyes and fillers—you may become overmedicated, as both of these are better absorbed than tablets.

Another possibility is that your pharmacist may have inadvertently given you the wrong dosage of medication or given incorrect instructions for use.

Lastly, if you are taking generic levothyroxine (which many doctors do not recommend), you may have gotten a more potent batch on your last refill. Even a slight change of potency from one refill to the next, particularly when refills come from different manufacturers of generic levothyroxine, can be enough to push you into hyperthyroidism.

Pay particular attention to symptoms that develop after a recent pharmacy refill. There may have been a medication error or change in the formulation.

Change in Diet

A change in your diet can affect proper absorption of thyroid hormone medication. For example, if you were eating a lot of fiber and then cut back on your intake, you may be absorbing higher levels of thyroid medication.

How and When to Take Thyroid Hormone Replacements

Supplements

Certain supplements can interfere with proper absorption of thyroid medications. Pay particular attention to supplements featuring the terms "thyroid support," "energy support," "thyroid glandulars," "adrenal glandulars," and "bovine glandulars." Some of these supplements contain actual thyroid hormone from animals and can result in overmedication. 

Supplements that contain iodine, bladderwrack (fucus vesiculosus), kelp, bugleweed, Irish moss, or seaweed are also culprits. Too much iodine, in particular, can aggravate your thyroid and trigger hyperthyroidism. 

Drugs that contain estrogens, such as hormone replacement medications and contraceptive pills, can interfere with thyroid hormone absorption. Hence, when you stop taking them, the absorption of your thyroid medications may increase, causing you to be overmedicated.

Hashimoto's Disease

If you have Hashimoto's disease, you may be in a period of fluctuation where the thyroid is overfunctioning and your thyroid's own hormone production, when added to your thyroid hormone replacement, is temporarily causing 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, the need for thyroid hormone drops, hence the amount of thyroid hormone replacement you were taking during pregnancy can become too high for the postpartum period, causing hyperthyroidism.

Monitoring for Overmedication

Doctors typically use your thyroid blood test results to assess whether you are getting too much medicine. In some cases, if your thyroid stimulating hormone (TSH) level is at the lower end of the reference range, or below the low end of normal (i.e., below 0.3 to 0.5), you will have symptoms of overmedication.

Being at the high end of or above the reference range for T4 and T3 levels can also point to overmedication.

What High and Low TSH Levels Mean

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 levels, and your symptoms of overmedication are eliminated.

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