Classic hallucinogens are a group of substances that alter perception, mood, and cognitive processes. Common examples include LSD, psilocybin (found in magic mushrooms), and mescaline (derived from the peyote cactus). These compounds primarily affect the serotonin receptors in the brain, leading to changes in sensory perception, thought patterns, and emotional experiences. Users of classic hallucinogens often report vivid visual and auditory hallucinations, altered sense of time, and profound introspective insights. While some people seek these experiences for recreational or spiritual purposes, it's important to note that the effects can vary widely and may lead to challenging psychological experiences, known as "bad trips."