In this chapter, we will describe the main hallucinogenic substances with therapeutic potential in neurological and psychiatric diseases, with emphasis on the most recent studies. The historical aspects of the use of each substance will also be addressed, discussing its mechanisms of action and the general effects produced. In addition, although this is not the focus of the chapter, we will comment on the mystical and religious use of some of the hallucinogens and cite their use as agents of creativity or other peculiar uses, when appropriate.