Levothyroxine: Side Effects, Interactions & Overdose

Instructor: Justine Fritzel

Justine has been a Registered Nurse for 10 years and has a Bachelor's of Science in Nursing degree.

Levothyroxine is a prescription medication that is frequently used for hypothyroidism. In this lesson, we will learn about side effects, drug interactions, and the risk of overdose.


The thyroid gland is responsible for producing hormones that impact metabolism. If your thyroid is not producing enough hormones, this is called hypothyroidism. These hormones affect the metabolism of every cell in the body, and if your levels are low, it slows down your body.

Thyroid Gland

Symptoms include feeling tired, feeling cold, weight gain, constipation, dry skin, and thin hair. You may also experience stiff and painful joints and muscles as well as depression. Hypothyroidism can be diagnosed through a blood test, and if your levels are too low, your doctor will likely start you on a prescription drug called levothyroxine.

Levothyroxine is the synthetic form of the hormones produced by the thyroid gland. When you take levothyroxine, it restores your hormone levels to where they should be. As with any medication, there are side effects and drug interactions that you should be aware of. Let's look at these next.

Things to Consider When Taking Levothyroxine

Side Effects

All medications have potential side effects. If you have ever listened to a drug commercial on TV or read the pamphlet that comes with a prescription, you understand the long list of possible side effects that may occur. This can seem so concerning that it makes you afraid to take the medication! But keep in mind, most people don't experience side effects, and the drug companies have to list any side effects that have occurred.

Common side effects associated with levothyroxine include anxiety, insomnia, nervousness, weight loss, and diarrhea. If you think back to the symptoms of hypothyroidism, you will recognize that these are the opposite of those symptoms. Therefore, the symptoms you experienced due to low thyroid levels may be the opposite symptoms once your levels are corrected. It may also indicate that you need a lower dose; your doctor will review blood levels to find the correct dosage for you.

Other common side effects include fast heart rate, tremor, nausea, fever, or headache. More serious side effects can affect your cardiac status and include irregular heart rate, congestive heart failure, high blood pressure, or chest pain.

If you experience any new or change in symptoms after starting levothyroxine, you should report these to your physician.

Drug Interactions

Any time you take more than one medication, you are at risk of experiencing drug interactions. It is essential to review all medications that you are taking with your physician and pharmacist. Don't forget to mention over-the-counter medications, supplements, vitamins, and herbs.

Levothyroxine should be taken on an empty stomach, preferably 30 minutes before breakfast. Certain medications will make levothyroxine less effective if they are taken at the same time. Therefore, you should take them at least four hours apart from the levothyroxine. Some of these medications include calcium, iron, and antacids.

There are several medications that may be affected by your thyroid levels or that affect the efficacy of levothyroxine. For example, amiodarone may have an effect on your thyroid hormone levels, and digoxin may have decreased levels when taken with levothyroxine. Omeprazole may decrease the effectiveness of the thyroid hormone.

Can You Overdose on Levothyroxine?

Levothyroxine is a beneficial medication for a person with hypothyroidism. But just because something is good, it doesn't mean that more is better. If you take too much levothyroxine, you will have symptoms of hyperthyroidism, which is when your thyroid is producing too many thyroid hormones.

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