Hallucinogens are a category of drugs that can cause altered perceptions such as sights, sounds, feelings, and the sense of time. They have been used throughout history by various cultures for spiritual purposes or medical use. Common hallucinogenic drugs include LSD, psilocybin mushrooms, PCP, mescaline, ketamine, and ecstasy. While some can be physically dangerous, all can potentially cause psychological dependence or long-term mental health issues from continued use. Side effects range from changes in mood to more severe reactions like convulsions or death.