Hallucinogens cause distortions of reality, particularly with sight, smell, and touch. Included in this category are LSD, mescaline, peyote, psilocybin mushrooms, and phencyclidine (PCP). Hallucinogens are normally swallowed, but PCP is usually smoked.

There is no evidence that hallucinogens cause a physical dependence; however, extended use may result in permanent brain damage. The most commonly abused hallucinogens are LSD and PCP.