A psychoactive or psychotropic drug was a chemical substance that altered brain functions and changed behavior and perception.
In 2373, Miles O'Brien and a team from Deep Space 9 discovered that soldiers from the Cardassian Third Battalion, First Order had been given large amounts of a psychotropic drug likely designed to heighten Cardassian xenophobia. Elim Garak came into contact with the drug and later killed Amaro while under the influence of it. (DS9 episode: "Empok Nor", DS9 comic: "Requiem in Obsidian")
In 2382, a Breen soldier told an inquisitor that they should use a psychoactive drug to gain information from Sarina Douglas, although the inquisitor was wary of doing so, due to their lack of knowledge of Human biochemistry. (ST - Typhon Pact novel: Zero Sum Game)