Psychedelics are powerful psychoactive substances that alter perception and mood and affect numerous cognitive processes, generating altered states of consciousness. They are generally considered physiologically safe and do not lead to dependence or addiction. Their origin predates written history and were employed by early cultures in many sociocultural and ritual contexts. Some people call psychedelics entheogens (chemical substances, typically of plant origin, ingested to produce a non-ordinary state of consciousness for spiritual purposes), plant medicines (substances made from botanicals, or plants, used to treat diseases or maintain health) or plant teachers (various psychoactive plants, traditionally used by Indigenous peoples for learning or wisdom).