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Overview: Liothyronine is used as a replacement hormone therapy for people with low thyroid hormone levels, among other uses. It supplies thyroid hormone to people who do not make enough. Liothyronine interacts with many medicines and health conditions. Always make sure your health care provider knows all of your health conditions and medicines you are taking, including over-the-counter (OTC) products. 

Uses

What is liothyronine used for?

Liothyronine is commonly used for the following conditions.

Liothyronine may also be used for other conditions as determined by your health care provider.

How does liothyronine work (mechanism of action)?

Liothyronine, also known as T3, provides a source of thyroid hormone in people who may not make enough on their own. Liothyronine may also be used for thyroid cancer. Taking it tells the thyroid gland to stop producing its own hormones, which can help stop the growth of thyroid cancer.

How is liothyronine supplied (dosage forms)?

Brands and other names

  • Cytomel

Dosage forms and strengths

  • 5 mcg, 25 mcg, 50 mcg oral tablets

How should I store liothyronine?

Liothyronine should be stored at room temperature, between 59 F and 86 F (15 C and 30 C). 

Side Effects

What are the most common side effects of liothyronine?

The most common side effects of liothyronine are listed below. Tell your health care provider if you have any of these side effects that bother you.

  • Arrhythmias, which are abnormal heart rhythms
  • Heart attack
  • Shortness of breath
  • Headache
  • Nervousness
  • Crankiness
  • Trouble sleeping
  • Tremors
  • Muscle weakness
  • Increased appetite
  • Weight loss
  • Diarrhea
  • Trouble tolerating heat
  • Menstrual changes
  • Rash

There may be other side effects of liothyronine that are not listed here. Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088 (800-332-1088). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of liothyronine?

While less common, the most serious side effects of liothyronine are described below, along with what to do if they happen.

Severe Allergic Reactions. Liothyronine may cause allergic reactions, which can be serious. Stop taking liothyronine and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Heart Problems. Liothyronine may cause your heart rate to increase or become abnormal. You may also have chest pain. Your risk may be higher if you are older, have heart problems, or if you take too much liothyronine. Tell your health care provider right away if you notice any of the following.

  • Chest pain or pressure
  • Fast or abnormal heartbeat
  • Shortness of breath

Weak Bones. Liothyronine may cause your bones to become weaker, leading to reduced bone density (osteopenia). It may also cause a more serious condition called osteoporosis, which can cause your bones to break (fracture) more easily. You may be at a higher risk of this if you take too much liothyronine or if you have gone through menopause. Tell your health care provider if you break a bone, and get a bone mineral density test if one is ordered for you.

Warnings & Precautions

Who should not use liothyronine?

Allergies to Ingredients. People who are allergic to any of the following should not take liothyronine.

  • Liothyronine
  • Cytomel
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific liothyronine products they stock.

Reduced Adrenal Function (Adrenal Insufficiency). You should not take liothyronine If you have reduced adrenal function that is not being treated. 

What should I know about liothyronine before taking it?

Do not take liothyronine unless it has been prescribed to you by a health care provider. Take it as prescribed. You should not take liothyronine to lose weight or for obesity.

Do not share liothyronine with other people, even if they have the same condition as you. It may harm them.

Keep liothyronine out of the reach of children.

People who are elderly may be at greater risk of some side effects from liothyronine. Talk to your health care provider about your risks if you are 65 years of age or older. 

You may notice hair loss while taking liothyronine, especially when you first start taking it. This is rare, and the hair loss is usually temporary. 

What should I tell my health care provider before taking liothyronine?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if liothyronine is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions. Tell your health care provider if you have any of the following. 

Pregnancy. It is not known if or how liothyronine could affect pregnancy or harm an unborn baby. Tell your health care provider if you are pregnant or plan to become pregnant. Your health care provider will let you know if you should take liothyronine while you are pregnant or trying to get pregnant. If you continue taking liothyronine during pregnancy, your health care provider may monitor your thyroid levels more often. 

Breastfeeding. Liothyronine passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed. Your health care provider will let you know if you should take liothyronine while breastfeeding.

Other Medicines and Supplements. Liothyronine may interact with other medicines and supplements. Before taking liothyronine, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Interactions

Does liothyronine interact with foods or drinks?

There are no known interactions between liothyronine and food or drinks. 

There are no known interactions between liothyronine and alcohol.

Does liothyronine interact with other medicines (drug interactions)?

Liothyronine interacts with many other medicines. Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before taking liothyronine.

  • Slow-release nicotinic acid or a bile acid sequestrant, such as colestipol (Colestid), cholestyramine (Prevalite), or colesevelam (Welchol), which is a medicine to lower cholesterol

  • Kayexalate, which is a medicine used to treat high potassium in the blood

  • Sevelamer, which is a medicine used to treat high phosphate in the blood

  • A hormone, such as estrogen (in birth control pills and hormone replacement therapy) or testosterone

  • Methadone, which is an opioid medicine used to treat pain or opioid use disorder

  • 5-fluorouracil (5-FU), asparaginase, mitotane, tamoxifen, and certain medicines known as tyrosine kinase inhibitors, which are chemotherapy agents that are used to treat or prevent certain cancers

  • A corticosteroid, such as dexamethasone, methylprednisolone, or prednisone, which is a medicine for certain inflammatory conditions

  • A salicylate, such as diflunisal or salsalate, which is a medicine used for osteoarthritis or rheumatoid arthritis

  • Phenobarbital, which is a medicine that may be used to treat seizures

  • A nonsteroidal anti-inflammatory drug (NSAID), such as ibuprofen, naproxen, and others, which are in many prescription and OTC products for pain, swelling, and fever

  • Rifampin, which is a medicine used to treat certain infections

  • A beta-blocker, such as atenolol (Tenormin), metoprolol (Lopressor, Toprol XL, and others), or propranolol (Inderal LA, Innopran XL), which is a medicine that may be used for certain heart conditions or to lower blood pressure

  • Digoxin (Lanoxin), which is a medicine used to treat irregular heartbeat and some types of heart failure

  • Amiodarone (Pacerone and others), which is a medicine used for an irregular heart rhythm

  • A medicine for diabetes

  • A blood thinner, which is a medicine used to treat or prevent blood clots

  • A tricyclic antidepressant or maprotiline, even if it is not used for depression

  • A weight loss medication, such as diethylpropion, phendimetrazine, or phentermine (Adipex-P, Lomaira, Qsymia) 

Some other medicines may alter the blood levels of liothyronine. Tell your health care provider about all medicines that you take or have recently taken.

This may not be a complete list of medicines that can interact with liothyronine. Always check with your health care provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much liothyronine?

If you or someone else has used too much liothyronine, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of liothyronine?

If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses.