Merck, T-075-1ML, 3,3′,5′-Triiodo-L-thyronine (Reverse T₃) solution

Reverse T3, also known as rT3 or 3,3′,5′-Triiodo-L-thyronine, is a biologically inactive form of the thyroid hormone T3 and is produced in the body particularly during periods of stress. Under certain conditions such as fibromyalgia, liver disease, and chronic fatigue syndrome (CFS), more rT3 is produced which minimizes the desirable conversion of thyroxine (T4) to T3. Reverse T3 serum concentrations are measured by LC-MS/MS to monitor impact of these and other diseases on thyroid hormone levels.