Liothyronine is a manufactured form of the thyroid hormone triiodothyronine. It is most commonly used to treat hypothyroidism and myxedema coma. It can be taken by mouth or by injection into a vein. Side effects may occur from excessive doses. This may include weight loss, fever, headache, anxiety, trouble sleeping, arrhythmias, and heart failure. Use in pregnancy and breastfeeding is generally safe. Liothyronine was approved for medical use in 1956. It is available as a generic medication. From Wikipedia