Psilocybin is a tryptamine compound with a chemical structure containing an indole ring linked to an ethylamine substituent. It is chemically related to the amino acid tryptophan, and is structurally similar to the neurotransmitter serotonin. Psilocybin is a member of the general class of tryptophan-based compounds that originally functioned as antioxidants in earlier life forms before assuming more complex functions in multicellular organisms, including humans. Other related indole-containing psychedelic compounds include dimethyltryptamine, found in many plant species and in trace amounts in some mammals, and bufotenine, found in the skin of psychoactive toads.