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. A drug's half-life is the time it takes for 50% of that drug to be removed from the body. 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. If a drug has active metabolites (these are breakdown products of the drug that still have an effect in the body) then a drug will last for longer in the body. Cytomel has no active metabolites and is excreted by the body mainly via the kidneys although a small portion is excreted in the feces.

Cytomel contains liothyronine in sodium salt form (also called LT3) which is a man-made form of a naturally occurring hormone produced by our thyroid glands called liothyronine. Cytomel may be used to increase levels of thyroid hormone in the body and treat thyroid deficiency disorders (hypothyroidism). It may also be given to help manage thyroid cancer in addition to surgery and radiotherapy, or to help diagnose conditions such as mild hyperthyroidism (high thyroid levels).