Liothyronine
Liothyronine (Cytomel) is a thyroid hormone used to treat an underactive thyroid and the severe thyroid emergency myxoedema coma. This page lists one tablet formulation: Cytomel.
Key points
- Liothyronine is a synthetic thyroid hormone that replaces the hormone the thyroid gland does not produce enough of.
- Cytomel is the only listed product, a 5mcg tablet marketed by the originator manufacturer Pfizer.
- The thyroid hormone affects nearly every system in the body, from heart rate to how food is turned into energy.
The hormone liothyronine is a synthetic form of triiodothyronine (T3), which the body uses to control how quickly cells use energy. As a tablet, it is one way to bring thyroid hormone levels back to normal.
Further reading
Related articles

29 Jul 2026 ⋅ 8 min read
Thyroid Problems: Why the Symptoms Are So Easy to Explain Away
An underactive thyroid causes tiredness, weight gain and feeling cold, symptoms mild enough to attribute to almost anything. What the blood tests measure, why levothyroxine is usually lifelong, and why the dose needs checking.
Read guide