Synthroid, Levothyroxine, Tirosint-sol, Thyquidity, Tirosint, Ermeza

Medically reviewed by Rosanna Sutherby, PharmD on April 18, 2023
Written by Amber Watson, PharmD

This article describes levothyroxine oral tablet’s uses and dosage, ways to save on cost, and more. Below you’ll find coupon options for levothyroxine.

Boxed warning: Not for weight loss or treatment of obesity

Levothyroxine has a boxed warning about the drug not being for weight loss or treatment of obesity. Boxed warnings are serious warnings from the Food and Drug Administration (FDA).

For details, see the “Warnings for levothyroxine” section below.

Levothyroxine may cause mild or serious side effects (also known as adverse effects). More common mild side effects of levothyroxine oral tablet and its serious side effects are listed below. This article doesn’t include all possible side effects of the drug. Side effects can vary based on your age and overall health and any other medications you take.

To learn more about levothyroxine oral tablet’s side effects, see this article or ask your doctor or pharmacist. You can also read the prescribing information for levothyroxine oral tablet.

Mild side effects

More common mild side effects reported with levothyroxine oral tablet are listed below.

With many drugs, mild side effects may go away within a few days or a couple of weeks. If the side effects are bothersome, tell your doctor or pharmacist. They may be able to suggest ways to manage them.

Levothyroxine oral tablet’s mild side effects include:

• diarrhea
• headache
• high sensitivity to heat
• weight loss or increased appetite
• trouble sleeping
• irregular periods
• muscle weakness, spasms, or tremors
• nervousness or irritability
• shortness of breath
• mild allergic reaction*

* For details about this side effect, see the “Warnings for levothyroxine” section below.

Serious side effects

Serious side effects of levothyroxine oral tablet are listed below. With many drugs, serious side effects are possible but not common.

If you have serious side effects from this drug, call your doctor right away. If you’re having severe symptoms or a medical emergency, call 911 or a local emergency number.

Levothyroxine oral tablet’s serious side effects include:

• heart problems, such as heart attack and heart failure
• low bone density
• severe allergic reaction*

*  For details about this side effect, see the “Warnings for levothyroxine” section below.

The dosage of levothyroxine oral tablet your doctor prescribes may vary based on your condition and certain other factors. These include your body weight, thyroid hormone levels, and other health conditions you may have. Talk with your doctor about the dosage you should take.

Taking levothyroxine

Levothyroxine oral tablet is swallowed. It should not be taken with food. You’ll take the drug on an empty stomach, usually 30 to 60 minutes before your first meal of the day.

Your doctor will talk with you about how and when to take levothyroxine oral tablet. They’ll explain how much to take and how often. Always follow your doctor’s recommendation.

See the “Common questions about levothyroxine” section for information on missed doses and the best time to take this drug.

Overdose of levothyroxine

You should not take more levothyroxine than your doctor prescribes. For some drugs, doing so may lead to serious side effects or overdose.

If you think you’ve taken too much levothyroxine, call your doctor or pharmacist right away. Or you could call 800-222-1222 to speak with someone at America’s Poison Centers. You can also use its online resource. If you have concerning symptoms, call 911 or a local emergency number immediately. You can also go to the closest emergency room.

The Food and Drug Administration (FDA) approves prescription drugs such as levothyroxine for certain conditions. Approved uses for levothyroxine oral tablet are described below.

Use for certain thyroid conditions

Doctors may prescribe levothyroxine oral tablet for hypothyroidism (underactive thyroid) and certain kinds of thyroid cancer. It’s used for these purposes in adults and children. The drug is usually prescribed as a long-term treatment.

With an underactive thyroid, your thyroid gland doesn’t make enough thyroid hormones. These hormones help manage many functions in your body, including body temperature, hair growth, and digestion. Having an underactive thyroid can cause these functions to slow down. Symptoms of an underactive thyroid can include low energy, depression, weight gain, and feeling cold.

With thyroid cancer, cancer cells begin growing in the thyroid but may spread to other areas of your body. Symptoms of thyroid cancer include a hoarse voice and having a nodule (lump), pain, or swelling in your neck.

Thyroid cancer may be treated with surgery to remove the thyroid. Or it may be treated with radioactive iodine to kill the cancer cells. Levothyroxine is used when thyroid cancer is treated with surgery or radioactive iodine.

Doctors may not prescribe levothyroxine oral tablet in certain situations, such as for:

• treating underactive thyroid in a person who’s recovering from subacute thyroiditis (a rare type of thyroid swelling)
• slowing the growth of noncancerous thyroid nodules or certain goiters (conditions that increase the size of your thyroid)
• treating myxedema coma (a rare but life threatening form of underactive thyroid)
• weight loss or treatment of obesity*

* Levothyroxine has a boxed warning about not using it for weight loss or obesity treatment. For more details, see the “Warnings for levothyroxine” section below.

Below you’ll find answers to a few commonly asked questions about levothyroxine oral tablet.

How does levothyroxine compare with other similar drugs, such as liothyronine?

Similar to levothyroxine, liothyronine belongs to a group of drugs called thyroid hormones. These medications are lab-made versions of the hormones that your thyroid gland makes naturally. They’re used when your thyroid doesn’t make enough hormones. They work by raising your thyroid hormone levels to a usual range.

Levothyroxine is used to replace a thyroid hormone called thyroxine (T4). It’s available in brand-name versions called Euthyrox, Levoxyl, Synthroid, and Unithroid.

Liothyronine (Cytomel) is used to replace a thyroid hormone called triiodothyronine (T3). And desiccated thyroid (Armour Thyroid) is used to replace both T3 and T4.

Your doctor can tell you which thyroid hormone drug is best for your condition. If you have more questions about how levothyroxine compares with similar drugs, talk with your doctor or pharmacist.

Can levothyroxine cause long-term side effects?

Yes, in some cases, levothyroxine may cause long-term side effects. These can lead to problems that last for a while after you’ve stopped taking the drug.

Examples of long-term side effects include:

• heart problems, such as heart attack and heart failure
• low bone density

Talk with your doctor to learn more about these side effects and how to best manage them. Ask your doctor for more information about how long these side effects of levothyroxine may last.

How does levothyroxine work? And how long does it take to start working?

Levothyroxine works by replacing the thyroxine (T4) hormone. T4 helps regulate the level of thyroid hormones in your body. Your body may not produce enough T4 due to underactive thyroid or treatment of certain kinds of thyroid cancer.

With levothyroxine treatment, your body is able to make more thyroid hormone to reach its usual levels. As a result, levothyroxine helps ease symptoms of an underactive thyroid. It also helps lower the risk of your thyroid cancer worsening or coming back after treatment. 

It may take 4 to 6 weeks for your thyroid hormone levels to reach their usual range after starting levothyroxine treatment. Your doctor will check your thyroid hormone levels with a blood test. They’ll use the test results to help determine whether the drug is working.

If you have questions about what to expect with levothyroxine treatment, talk with your doctor.

Does levothyroxine cause eye-related side effects?

Eye-related side effects were not reported in studies of levothyroxine.

But eye symptoms can be a sign of overactive thyroid, which can happen if you take too much levothyroxine. This is because levothyroxine is a lab-made version of a hormone that your thyroid gland makes naturally. And taking more levothyroxine than your doctor recommends can lead to an overactive thyroid. Eye symptoms of overactive thyroid may include:

• double or blurred vision
• dry eyes
• pressure or pain in the eyes, or bulging eyes

To lower your risk of eye symptoms from taking too much levothyroxine, be sure to take the drug exactly as your doctor recommends. If you have any of the eye symptoms above, talk with your doctor. They can give you a blood test to check your thyroid hormone levels. The test results will help your doctor decide whether they should lower your levothyroxine dosage.

Is there a best time of day to take levothyroxine? What should I do if I miss a dose of levothyroxine?

Yes, there’s a best time of day to take levothyroxine. You’ll take the drug 30 to 60 minutes before your first meal of the day. The drug works best if it’s taken on an empty stomach.

If you miss a dose of levothyroxine, contact your doctor or pharmacist. They can recommend when it’s best to take the next dose of the drug.

Can levothyroxine tablets be crushed, split, or chewed?

Levothyroxine tablets can be crushed or split. But the drugmaker has not stated whether it’s safe to chew the tablets.

If you’re unable to swallow a levothyroxine tablet whole, you can split the tablet in half using the score line printed across the tablets. Or you may crush the levothyroxine tablet and dissolve it in 1 or 2 teaspoons of water. You’ll swallow this mixture right away. Do not store it for later use.

It’s also important that you do not mix levothyroxine tablets with any food. This is because the drug works best when it’s taken on an empty stomach. You’ll take the drug 30 to 60 minutes before your first meal of the day.

If you have questions about crushing or splitting levothyroxine tablets, talk with your doctor or pharmacist.

Levothyroxine should be taken cautiously by certain people. Precautions for taking this drug are described below.

Boxed warning: Not for weight loss or treatment of obesity

Levothyroxine has a boxed warning about the drug not being used for weight loss or the treatment of obesity. Boxed warnings are serious warnings from the Food and Drug Administration (FDA).

Doctors will not prescribe levothyroxine oral tablets for weight loss or the treatment of obesity. This is because the dosages required for weight loss and obesity could lead to serious side effects. These include feeling confused or disoriented, or having seizures or a blood clot in the brain. In some cases, these side effects could be life threatening.

If you’re interested in treatment options for weight loss or obesity, talk with your doctor. They’ll recommend the best options for you.

To learn more, talk with your doctor or pharmacist.

Other warnings

Levothyroxine could cause harm to people with certain health conditions. This effect is called a drug-condition interaction. Other factors can also affect whether levothyroxine oral tablet is a safe option for you.

Tell your doctor about your overall health and any past health conditions before you take levothyroxine oral tablet. Health conditions and other factors you and your doctor should discuss include:

• heart disease
• adrenal insufficiency 
• diabetes

Allergic reaction

Levothyroxine can cause an allergic reaction in some people. Severe allergic reactions are rare but possible.

If you’ve had an allergic reaction to levothyroxine or any of its ingredients, your doctor will likely not prescribe levothyroxine. They can tell you about medications that are safer options for you.

A mild allergic reaction may cause the following symptoms:

• skin rash
• itchiness
• flushing (temporary warmth, redness, or deepening of skin color)

A severe allergic reaction may cause the following symptoms:

• swelling under your skin, usually in your hands, feet, eyelids, or lips
• swelling of your mouth, throat, or tongue, which can cause breathing problems

If you have an allergic reaction to levothyroxine, call your doctor right away. If you have severe symptoms, call 911 or a local emergency number.

For some medications, certain things may affect how the drug works. These include getting vaccines, consuming alcohol or certain foods, or taking the drug with other medications. This effect is called a drug interaction.

Before you take levothyroxine, ask your doctor to check for possible interactions. They can check for interactions these items may cause with levothyroxine. Be sure to tell them about any of the following you take or use:

• prescription medications
• over-the-counter medications
• vitamins, herbs, or supplements

To learn about drug-condition interactions, see the “Warnings for levothyroxine” section below.

Information about levothyroxine and pregnancy and breastfeeding is described below.

Levothyroxine and pregnancy

In general, levothyroxine oral tablet is considered safe to take during pregnancy. That said, check with your doctor about whether they feel it’s safe for you specifically.

Levothyroxine and breastfeeding

It’s not known whether levothyroxine oral tablet should be taken while breastfeeding. If you’re currently breastfeeding or planning to do so, talk with your doctor before taking this medication.

You may be able to save money on your prescription for levothyroxine oral tablet by using our Perks discount coupons. These can be found at the end of this article.

If you have questions about how to pay for levothyroxine, talk with your doctor or pharmacist. You can also learn more about the cost of levothyroxine in this article.

Note: Optum Perks coupons cannot be used with insurance copays or benefits.

This article describes levothyroxine oral tablet’s uses and dosage, ways to save on cost, and more. Let your doctor know if you have questions about levothyroxine or would like more details about it.

Here’s a list of some possible questions you may want to ask your doctor:

• Should I take levothyroxine with any other treatments for my condition?
• Does levothyroxine interact with any other drugs I’m taking?
• Will levothyroxine cure my condition?

• Food and Drug Administration. (2023). Orange Book: Approved drug products with therapeutic equivalence evaluations. https://www.accessdata.fda.gov/scripts/cder/ob/index.cfm
• Levothyroxine sodium tablets, for oral use. (2023). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/f6c92836-95e1-1402-e053-6394a90a2f5e/spl-doc

Disclaimer: Optum Perks has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.