Psychedelic drugs, also known as hallucinogenic drugs, or simply hallucinogens, are a group of substances, including chemicals, such as LSD, and plants, such as peyote, that are usually used recreationally, to change and enhance sensory perceptions, thought processes, energy levels, and to facilitate spiritual experiences. Psychedelics have also been used experimentally to mimic psychosis and to exert mind control, although they have not been found to be particularly effective in doing either. They were used in psychotherapy in the 1960s, but this was halted for mainly political reasons until quite recently, and psychological research has undergone a revival of the use of psychedelics in experimental psychological treatment. There are numerous psychedelic substances, used in many different cultures. Here are some of the best-known varieties: