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Cytomel Side Effects

Generic Name: liothyronine

Note: This page contains information about the side effects of liothyronine. Some of the dosage forms included on this document may not apply to the brand name Cytomel.

For the Consumer

Applies to liothyronine: oral tablet

In addition to its needed effects, some unwanted effects may be caused by liothyronine (the active ingredient contained in Cytomel). In the event that any of these side effects do occur, they may require medical attention.

If any of the following symptoms of overdose occur while taking liothyronine, get emergency help immediately:

  • Arm, back or jaw pain
  • changes in appetite
  • changes in menstrual periods
  • chest pain or discomfort
  • chest tightness or heaviness
  • cold clammy skin
  • confusion
  • decreased urine output
  • diarrhea
  • dilated neck veins
  • dizziness
  • extreme fatigue
  • fainting
  • fast, slow, pounding, or irregular heartbeat or pulse
  • fever
  • hand tremors
  • headache
  • increased bowel movements
  • irregular breathing
  • irritability
  • leg cramps
  • lightheadedness
  • menstrual changes
  • nausea
  • nervousness
  • sensitivity to heat
  • shortness of breath
  • sweating
  • swelling of face, fingers, feet, or lower legs
  • troubled breathing
  • trouble sleeping
  • vomiting
  • weak pulse
  • weight gain
  • weight loss
  • wheezing

For Healthcare Professionals

Applies to liothyronine: compounding powder, intravenous solution, oral tablet


Liothyronine is generally well tolerated. Side effects associated with liothyronine (the active ingredient contained in Cytomel) therapy typically result from therapeutic overdosage and include manifestations of hyperthyroidism such as weight loss, increased appetite, diarrhea or increased bowel frequency, insomnia, nervousness, irritability, tremor, excessive sweating, heat intolerance, palpitations, hypertension, tachycardia, chest pain, and menstrual irregularities.[Ref]


Cardiac function was evaluated in twenty patients requiring TSH suppression for either thyroid goiter or following thyroidectomy and radioactive iodine therapy for thyroid cancer and in twenty age- and sex-matched controls. TSH suppression was associated with an increased incidence of premature ventricular beats, an increased left ventricular mass index, and enhanced left ventricular systolic function. The clinical significance of these changes remains to be determined.[Ref]

Cardiovascular side effects of thyroid hormone therapy have included palpitations, hypertension, tachycardia, and angina, all of which may be exacerbated in patients with underlying cardiovascular disorders. In the treatment of myxedema coma/precoma, cardiovascular side effects associated with the use of intravenous liothyronine have included arrhythmia (6%), tachycardia (3%), cardiopulmonary arrest (2%), hypotension (2%), and myocardial infarction (2%). Angina, congestive heart failure, hypertension, and phlebitis have occurred in approximately 1% or fewer of patients.[Ref]


Endocrine side effects of thyroid hormone therapy have included changes in symptom presentation for diabetes and adrenal cortical insufficiency. Treatment measures of these conditions may require adjustment.[Ref]

Nervous system

Nervous system side effects of thyroid hormone therapy have rarely included seizures during initiation of therapy. In the treatment of myxedema coma/precoma, twitching has been reported in approximately 1% or fewer of patients treated with intravenous liothyronine (the active ingredient contained in Cytomel) [Ref]


Dermatologic side effects of thyroid hormone therapy have included transient hair loss during the initial months of therapy. Rarely, allergic skin reactions have been reported with liothyronine (the active ingredient contained in Cytomel) [Ref]


Musculoskeletal side effects of thyroid hormone therapy have included an increased risk of osteoporosis. However, data from long-term studies are conflicting.[Ref]

A study evaluated the effect of long-term thyroid hormone therapy on bone mineral density in 196 women (mean age, 74.4 years) compared to a control group comprised of 795 women (mean age, 72.1 years). The mean daily thyroxine dose was 1.99 mcg/kg (range, 0.3 to 6.6 mcg/kg) and the mean duration of therapy was 20.4 years (range, less than 1 to 68 years). Women taking daily doses of 1.6 mcg/kg or more had significantly lower bone mineral density levels at the ultradistal radius, midshaft radius, hip, and lumbar spine compared to controls. However, estrogen use appeared to negate the adverse effects of thyroid hormone on bone mineral density.

Higher rates of femur fractures have been found in males (p=0.008) prescribed long-term thyroid hormone therapy as compared to controls in a case-control analysis of 23,183 patients from the United Kingdom General Practice Research Database.[Ref]


1. Leese GP, Jung RT, Guthrie C, Waugh N, Browning MC "Morbidity in patients on L-thyroxine: a comparison of those with a normal TSH to those with a suppressed TSH." Clin Endocrinol (Oxf) 37 (1992): 500-3

2. "Product Information. Synthroid (levothyroxine)." Abbott Pharmaceutical, Abbott Park, IL.

3. Haynes RC. Thyroid and antithyroid drugs. In: Goodman Gilman A, Rall TW, Nies AS, Taylor P, eds. "Goodman and Gillman's: the Pharmacologic Basis of Therapeutics." New York, NY: Pergamon Press (1990): 1361-83

4. "Product Information. Cytomel (liothyronine)." SmithKline Beecham, Philadelphia, PA.

5. Petersen K, Bengtason C, Lapidus L, et al "Morbidity, mortality, and quality of life for patients treated with levothyroxine." Arch Intern Med 150 (1990): 2077-81

6. "Product Information. Triostat (liothyronine)." Jones Pharma Inc, St. Louis, MO.

Not all side effects for Cytomel may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

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