Hallucinogens are a class of substances that alter a person's perception, mood, and cognitive processes. They can cause visual and auditory hallucinations, leading to experiences that may feel very real but are not based in reality. Common hallucinogens include LSD, psilocybin (found in certain mushrooms), and mescaline (derived from the peyote cactus). These substances work by affecting neurotransmitters in the brain, particularly serotonin. While some people use hallucinogens for recreational purposes or spiritual experiences, they can also pose risks, including anxiety, paranoia, and potential long-term psychological effects.