A psychedelic drug or classical hallucinogen is a substance whose primary action is to alter cognition and perception, typically as a serotonin receptor agonist, causing thought and visual/auditory changes, and heightened state of consciousness. Major psychedelic drugs include LSD, mescaline (peyote's active ingredient), DMT and hallucinogenic mushrooms. Differing with other psychoactive drugs, such as stimulants and opioids, psychedelics tend to qualitatively alter ordinary conscious experience. Whereas stimulants cause energized feelings and opioids produce a relaxed euphoric state, the psychedelic experience is often compared to non-ordinary forms of consciousness such as trance, meditation, yoga, religious ecstasy, dreaming and even near-death experiences. Most psychedelic drugs fall into one of the three families of chemical compounds: tryptamines, phenethylamines, or lysergamides. Many psychedelic drugs are illegal worldwide under the UN conventions, occasionally excepting use in a religious or research context. Despite these controls, recreational use of psychedelics is common.