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Generic name: liothyronineLYE-oh-THYE-roe-neen ]
Drug class: Thyroid drugs

Medically reviewed by on Feb 13, 2023. Written by Cerner Multum.

What is Cytomel?

Cytomel is a man-made form of a hormone that is normally produced by your thyroid gland to regulate the body's energy and metabolism. This medicine is given when the thyroid does not produce enough of this hormone on its own.

Cytomel treats hypothyroidism (low thyroid hormone). This medicine is also given as part of a medical test for thyroid disorders.

Cytomel is also used together with surgery and radioactive iodine therapy in people with thyroid cancer.

Cytomel should not be used to treat obesity or weight problems.

Cytomel may also be used for purposes not listed in this medication guide.


Cytomel should not be used to treat obesity or weight problems.

You may not be able to use Cytomel if you have an adrenal gland problem that is not controlled by treatment.

Stop taking Cytomel and call your doctor if you have symptoms of thyroid toxicity, such as chest pain, fast or pounding heartbeats, feeling hot or nervous, or sweating more than usual.

Before taking this medicine

Since thyroid hormone occurs naturally in the body, almost anyone can take Cytomel. However, you may not be able to use this medicine if you have an adrenal gland problem that is not controlled by treatment.

Tell your doctor if you have ever had:

  • problems with your pituitary or adrenal gland;

  • heart disease, angina (chest pain);

  • a bleeding or blood clotting disorder;

  • diabetes; or

  • osteoporosis or low bone mineral density.

Tell your doctor if you are pregnant or breastfeeding.

Follow your doctor's instructions about using this medicine if you are pregnant. Controlling your thyroid hormone levels is very important during pregnancy, and your dose needs may be different during each trimester.

How should I take Cytomel?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.

Older adults may be more sensitive to the effects of liothyronine, and doses are generally lower for people in this age group.

If you are switching to Cytomel from any other thyroid medicine, stop using the other medicine before you start taking this medicine.

Cytomel doses are based on weight (especially in children and teenagers). Your dose needs may change if you gain or lose weight.

When given as part of a thyroid suppression test, you will need to take Cytomel for several days in a row in preparation for the test. Tell your doctor if you miss any doses during this time.

Your thyroid function will need to be tested often. Even if you have no symptoms, tests can help your doctor determine if this medicine is effective.

If you need surgery, tell your surgeon you currently use this medicine. You may need to stop for a short time.

This medicine can affect the results of certain medical tests. Tell any doctor who treats you that you are using Cytomel.

Keep using this medicine as directed, even if you feel well. You may need to take thyroid medication for the rest of your life.

Store at room temperature away from moisture and heat.

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose symptoms may include headache, sweating, diarrhea, irregular menstrual periods, confusion, weakness, swelling in your hands or feet, fast heart rate, chest pain, feeling short of breath, fainting, or feeling nervous, restless, or irritable.

What should I avoid while taking Cytomel?

Do not change brands or change to a generic product without first asking your doctor. Different brands of liothyronine may not work the same. If you get a prescription refill and your new pills look different, talk with your pharmacist or doctor.

Cytomel side effects

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Stop using Cytomel and call your doctor if you have symptoms of thyroid toxicity, such as chest pain, fast or pounding heartbeats, feeling hot or nervous, or sweating more than usual.

Also call your doctor at once if you have:

  • weak or shallow breathing;

  • confusion;

  • a feeling of being cold all the time;

  • changes in weight or appetite;

  • chest pressure spreading to your jaw or shoulder;

  • a light-headed feeling, like you might pass out;

  • severe headaches, ringing in your ears, dizziness, vision problems, pain behind your eyes;

  • a seizure; or

  • (in a child or teenager) pain, stiffness, and trouble moving the legs.

Common side effects of Cytomel may include:

  • trouble breathing;

  • headache;

  • tremors, feeling nervous or irritable;

  • muscle weakness;

  • increased appetite;

  • diarrhea;

  • irregular menstrual periods;

  • weight loss;

  • feeling hot;

  • rash; or

  • sleep problems (insomnia).

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What other drugs will affect Cytomel?

Some medicines can make Cytomel much less effective when taken at the same time. If you take any of the following medicines, take your this medicine dose 4 hours before you take the other medicine.

Tell your doctor about all your current medicines. Many drugs can affect Cytomel, especially:

This list is not complete and many other drugs may affect Cytomel. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

Popular FAQ

Although the American Thyroid Association guidelines do not recommend taking Cytomel and Synthroid together, many people who are under the supervision of an internist/endocrinologist do take this combination treatment, prefer it, and have good results on it. Never take this combination without your doctor's advice because it may result in excessive levels of thyroid hormones which can be dangerous. Continue reading

Cytomel starts working within a few hours, but its maximum effect can take two to three days to occur. It only takes 4 hours for 95% of a dose of Cytomel to be totally absorbed. If you are taking Cytomel daily, then after a few days it will work continuously, without any drop in effect, and you should notice a reduction in your symptoms of hypothyroidism within 2 to 3 days. Continue reading

Although Cytomel does help with weight loss in people prescribed it for hypothyroidism (low thyroid levels), it is not effective at usual dosages at reducing weight in people with normal thyroid levels. Using high dosages of Cytomel to reduce weight in people with normal thyroid levels is dangerous, not safe, and can be life-threatening. Strokes, seizures, shock, coma and death have been reported in people who have taken higher than recommended dosages of Cytomel.  Continue reading

Cytomel stays in your system for up to 12.5 days following the last dose. Experts calculate this period using the half-life of a drug. The half-life of Cytomel is about 2.5 days and experts agree that it takes up to 5 half-lives for a drug without active metabolites to be completely removed from the body. This calculates out to 12.5 days for Cytomel.  Continue reading

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Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.