Thiomescaline (TM) is a pair of lesser-known psychedelic drugs with the molecular formula C11H17NO2S. 3-TM and 4-TM are analogs of mescaline in which an oxygen atom has been replaced with a sulfur atom. They were first synthesized by Alexander Shulgin and described in his book PiHKAL.[1][2] Very little data exists on the pharmacological properties, metabolism, and toxicity of thiomescaline.[citation needed]