Many pharmacologists define psychedelic drugs as chemicals which have an LSD or mescaline like action on certain serotonin receptors. Over the decades, the term has been contaminated to include far more substances than originally intended. The best definition of what is considered a classic or true psychedelic is the following - “a psychedelic drug is one which, without causing physical addiction, craving, major physiological disturbances, delirium, disorientation, or amnesia, more or less reliably produces thought, mood, and perceptual changes otherwise rarely experienced except in dreams, contemplative and religious exaltation, flashes of vivid involuntary memory and acute psychoses”. At high levels this can overwhelm the sense of self and can result in a dissociative state.
This effect is sometimes referred to as mind expanding, or consciousness expanding as your conscious mind becomes aware of (or sometimes assaulted by) things normally inaccessible to it. These signals are presumed to originate in several other functions of the brain, including but not limited to the senses, emotions, memories and the unconscious (or subconscious) mind. Psychedelic drugs are thought to disable filters which block or suppress signals related to mundane functions from reaching the conscious mind. The term is derived from Greek ψυχη ( psyche, "mind") and δηλειν ( delein, "manifest"). Psychedelic drugs are psychoactive drugs whose primary action is to enhance or amplify the thought processes of the brain.