Side effects

Liothyronine therapy generally is well-tolerated. If symptoms occur, they usually occur because there are toxic (too high) levels of thyroid hormone (hyperthyroidism). Symptoms of hyperthyroidism include: chest pain, increased heart rate, cardiac arrest, excessive sweating, heat intolerance, nervousness, headache, tremor, insomnia, diarrhea, vomiting, weight loss, or fever. Women also may experience irregular menstrual cycles.

Since thyroid hormone affects heart rate and metabolism, the impact of treatment of thyroid hormone on the control of diseases such as atrial fibrillation, diabetes and high cholesterol levels always should be considered.