What are the side effects of levothyroxine?

Side effects of levothyroxine can include hair loss, headache, diarrhea, fever, weight gain or loss, vomiting, joint pain, heat sensitivity, appetite changes, menstrual cycle changes, and leg cramps. Serious side effects that could warrant visiting a provider include wheezing, shortness of breath, hives, rash, and swelling of the hands, feet, ankles, or lower legs.

What is the recommended dosage for levothyroxine?

There is not one recommended dosage for levothyroxine because each patient's body works differently. In many cases, people who start receiving treatment for hypothyroidism will be given a lower dose of medication to avoid the risk of overmedicating. Over time, their dose will likely need to be adjusted to meet their individual needs.

What are the dangers of too much thyroid medication?

There are many risks of taking too much levothyroxine. The signs and symptoms of thyroid overmedication include anxiety, diarrhea, depression, elevated heartbeat, elevated blood pressure, fatigue, irritability, difficulty concentrating, difficulty sleeping, being overheated, and unprompted or unintentional weight loss.

Are You Taking Too Much Levothyroxine?

Learn the symptoms of too much thyroid medication

By Mary Shomon

Updated on March 01, 2023

Medically reviewed by Danielle Weiss, MD

Thyroid hormone replacement medications like levothyroxine are used to treat hypothyroidism—a condition that occurs because your thyroid gland does not produce enough thyroid hormones.

Taking too much levothyroxine can cause side effects. The signs and symptoms of taking too much thyroid medication can look like hypothyroidism and can include an elevated pulse, fatigue, and diarrhea.

If you're having these symptoms, tell your healthcare provider. They can help you find the dose of levothyroxine that's safe and effective for you.

This article will go over how you might end up taking too much levothyroxine, the side effects of levothyroxine overmedication, and when to see a healthcare provider.

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 desiccated thyroid (NDT) is also used to treat hypothyroidism. For some people, NDTs work better than levothyroxine. Many people prefer NDTs because they are considered more natural. Brand names NDTs include Armour and Nature-Throid.

Usually, people start thyroid hormone therapy by taking a low dose and gradually increasing it. Since hypothyroidism progresses over time, starting therapy with a low dose is helpful for reducing the risk of overmedication.

If you're prescribed levothyroxine, your provider will tell you how much to take. Still, it's possible to take too much levothyroxine by accident.

How Is Hypothyroidism Treated?

1:41

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This video has been medically reviewed by Rochelle Collins, DO.

Symptoms of Taking Too Much Levothyroxine

The signs and symptoms of thyroid hormone overmedication can vary but may include:

Elevated pulse and blood pressure
Anxiety, nervous energy, tremors
Feeling irritable, overemotional, erratic, or depressed
Difficulty concentrating
Difficulty sleeping
Fatigue or feeling extremely tired
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 or exercise routine
Increase in food intake with no weight gain

In some cases, the symptoms and side effects of taking too much levothyroxine are similar to those of hypothyroidism. For example, you may feel more exhausted than usual, feel achy (as if you have the flu), or feel jittery and anxious. You may also gain weight.

It's not unheard of for a person to go to their healthcare provider because they think they need a higher dose of their medication only to find out their symptoms are actually being caused by thyroid overmedication.

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How Levothyroxine Overmedication Happens

There are a number of ways you can end up taking too much levothyroxine. Sometimes, it takes trial and error to get your dosage just right. Prescribing mistakes can happen as well.

Dosage or Drug Quality Issues

You could take too much levothyroxine because you are taking the wrong dose.

For example:

Your healthcare provider 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 potent or less potent than your previous refill. Even a slight change of potency from one refill to the next can lead to over or under medication and symptoms of hyper or hypothyroidism.

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

For example, Tirosint liquid gel caps and Tirosint-SOL liquid levothyroxine are absorbed better than levothyroxine in tablet form. You might be prescribed gel-cap or liquid levothyroxine if you are allergic to dyes or fillers, but making the switch could result in overmedication.

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

Pay attention to any symptoms that start after you've refilled your prescription at the pharmacy, as they could be a sign of a medication error or change in the formulation.

Diet Changes

Sometimes, you end up getting too much levothyroxine because of factors that are not directly related to the medication.

For example, changing your diet can affect how well your body absorbs thyroid hormone medication.

One situation where this could occur would be if you cut back on your fiber intake. When you make this change, you might start to absorb higher levels of thyroid medication.

Supplements and Medications

Taking certain supplements can add to the effects of your thyroid replacement medication and lead to you taking too much levothyroxine.

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 hormones from animals.

Supplements that contain iodine, such as bladderwrack (Fucus vesiculosus), kelp, bugleweed, Irish moss, or seaweed can also cause problems. Too much iodine, in particular, can overstimulate your thyroid and trigger hyperthyroidism.

Drugs that contain estrogens, such as hormone replacement medications and oral contraceptive pills, can also interfere with thyroid hormone requirements. When you stop taking them, your body might need more or less thyroid medication than when you were taking them.

Hashimoto's Disease

Medical conditions can also lead you to have too much levothyroxine in your body. With Hashimoto's disease, your thyroid hormone levels can fluctuate rapidly. Hashitoxicosis is 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 symptoms of hyperthyroidism.

Pregnancy

You might have too much levothyroxine in your body if you've recently been pregnant. During pregnancy, your need for thyroid hormone increases. You may need to be prescribed a higher dose of medication than you usually take during this time.

However, your need for thyroid hormone decreases once you give birth. The dose of thyroid hormone replacement that you were taking during pregnancy could be too high for the postpartum period and could lead to overmedication.

Monitoring for Overmedication

To avoid overmedication with levothyroxine, your healthcare provider will use your thyroid blood test results to see if you are getting too much. 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.

When to See a Healthcare Provider

Contact your healthcare provider if you're experiencing symptoms of too much levothyroxine. They can do tests to check your thyroid levels and figure out if you’re being overmedicated.

If your provider determines that you are taking too much levothyroxine, they will reassess your treatment plan. They might advise you to change your diet if it's contributing to thyroid overmedication. Your provider might also change your medication or adjust your dose.

How to Take Your Thyroid Medication

Summary

There are a few reasons you could end up taking too much levothyroxine. For example, you may become overmedicated with changes in the dosage or type of thyroid hormone replacement therapy you are taking. Certain health conditions and lifestyle changes can also make an overdose of levothyroxine more likely to happen.

The signs, symptoms, and side effects of too much levothyroxine can mimic hyperthyroidism or hypothyroidism, so it's important to have your TSH, T4, and/or T3 levels checked regularly and any time your medication changes.

A Word From Verywell

The symptoms of being overmedicated with thyroid hormone replacement drugs are uncomfortable but rarely dangerous. Eliminating thyroid-boosting supplements and/or cutting back on your medication dosage can help you avoid taking too much levothyroxine.

Your healthcare provider will run thyroid tests from time to time and adjust your dosage as needed until your symptoms get better and your thyroid levels return to the levels they should be at.

Frequently Asked Questions

What are the side effects of levothyroxine?

Side effects of levothyroxine can include hair loss, headache, diarrhea, fever, weight gain or loss, vomiting, joint pain, heat sensitivity, appetite changes, menstrual cycle changes, and leg cramps.
Serious side effects that could warrant visiting a provider include wheezing, shortness of breath, hives, rash, and swelling of the hands, feet, ankles, or lower legs.
What is the recommended dosage for levothyroxine?

There is not one recommended dosage for levothyroxine because each patient's body works differently.
In many cases, people who start receiving treatment for hypothyroidism will be given a lower dose of medication to avoid the risk of overmedicating. Over time, their dose will likely need to be adjusted to meet their individual needs.
What are the dangers of too much thyroid medication?

There are many risks of taking too much levothyroxine. The signs and symptoms of thyroid overmedication include anxiety, diarrhea, depression, elevated heartbeat, elevated blood pressure, fatigue, irritability, difficulty concentrating, difficulty sleeping, being overheated, and unprompted or unintentional weight loss.

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