Abstract The effects of para‐chlorophenylalanine (PCPA) and 3,4 methylenedioxy‐methamphetamine (MDMA, ‘ecstasy’) were investigated in relation to development, behavior and physiology in larval Drosophila . PCPA blocks the synthesis of serotonin (5‐HT) and MDMA is known to deplete 5‐HT in mammalian neurons; thus these studies were conducted primarily to target the serotonergic system. Treatment...