Thioridazine, sold under trade names Mellaril, Novoridazine, and Thioril, is a piperidine typical antipsychotic drug used in the treatment of schizophrenia and psychosis. Thioridazine is supposed to cause severe cardiac arrhythmias. This stable-labeled internal standard is suitable for quantification of Thioridazine levels in LC-MS/MS or GC-MS testing applications.