Liothyronine is a synthetic form of triiodothyronine (T3), the active thyroid hormone. It is sold as Cytomel and generic tablets.
Also known as: Cytomel, T3.
Cytomel tablets come in 5 mcg, 25 mcg and 50 mcg strengths.
The FDA Cytomel label approves liothyronine for hypothyroidism (primary, secondary or tertiary), to suppress TSH alongside treatment of certain thyroid cancers, and as a diagnostic thyroid suppression test. For hypothyroidism in adults it starts at 25 mcg once daily, raised by up to 25 mcg every 1 to 2 weeks, with a usual maintenance dose of 25 to 75 mcg once daily. Older people and people with heart disease start at 5 mcg.
The label carries a boxed warning: not for treatment of obesity or for weight loss. It says T3 acts within a few hours, and that bile acid sequestrants should be taken at least 4 hours after Cytomel.
The FDA Cytomel label gives a biological half-life of about 2.5 days; Dose Track uses 60 hours. The Synthroid label lists the T3 half-life as 2 days or less. The Cytomel label gives no time to peak; it says about 95% is absorbed within 4 hours. In single-dose studies T3 peaked 2.5 hours after 50 mcg (Jonklaas 2015) and 2.3 to 2.4 hours after 20 mcg (Leggio 2006); Dose Track uses 2.5 hours.
Numbers shown are the values Dose Track uses, listed only where they agree with the source above. Half-life varies from person to person and with injection site.