Liothyronine - Cytomel - Synthetic T3 - Thyroid Drugs

liothyronine, T3, cytomel


Liothyronine is a synthetic drug version of the thyroid hormone triiodothyronine, also known as T3.

T3 is the active thyroid hormone - while T4 (thyroxine) is the storage hormone. T4 needs to be converted into T3 in order to deliver oxygen and energy to the cells, tissues, and organs.

Liothyronine is available in a generic form, as well as one brand name, Cytomel, made by Pfizer Pharmaceuticals, in the United States.

Use of synthetic T3 is controversial, as levothyroxine (synthetic T4) is the preferred treatment for hypothyroidism. Some studies have shown that some patients preferred combination T4/T3 therapies however.


According to FDA information, the following are the potential side effects of liothyronine:

  • temporary hair loss
  • increased sensitivity
  • hives
  • difficulty breathing/shortness of breath
  • chest pain
  • irregular heartbeat
  • leg cramps
  • excessive sweating
  • sensitivity to heat
  • vomiting
  • diarrhea
  • nervousness
  • headache
  • tremors
  • changes in menstrual cycle


  • Vitamins containing iron should be taken 4 hours away from this medication
  • If you take lanthanum, separate by at least 2 hours from liothyronine
  • products that contain aluminum/magnesium, antacids, sucralfate, calcium supplements, iron, bile acid-binding resins (such as cholestyramine, colestipol, colesevelam), simethicone, sevelamer, sodium polystyrene sulfonate) should be taken 4 hours away from liothyronine

    The following medications may cause an adverse reaction with liothyronine:

    • oral contraceptives or hormone replacement medication
    • blood thinners
    • aspirin
    • insulin/oral diabetes medication
    • antidepressants
    • medications containing iodine
    • steroids


    Manufacturer: Pfizer
    Drug Site:
    Patient Resources:
    Consumer Hotline: 800-438-1985 / 212-733-2323
    RxList Listing: 
    FDA Guidance: on liothyronine

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