The thiazolidinediones /θaɪ.əˌzoʊlɪdiːnˈdaɪ.oʊn/, abbreviated as TZD, also known as glitazones after the prototypical drug ciglitazone,[1] are a class of heterocyclic compounds consisting of a five-membered C3NS ring. The term usually refers to a family of drugs used in the treatment of diabetes mellitus type 2 that were introduced in the late 1990s. As of 2024, there are two FDA-approved drugs in this class, pioglitazone and rosiglitazone.[2]