A hallucinogenic drug, also known as a hallucinogen or psychedelic, is a substance that alters perception, thought, mood, and consciousness. These drugs cause changes in the way people see, hear, taste, smell, or feel, often leading to hallucinations—sensations and images that appear real but are not. Hallucinogens can be natural or synthetic and are classified into categories such as psychedelics (e.g., LSD, psilocybin), dissociatives (e.g., ketamine, PCP), and deliriants (e.g., scopolamine). They produce altered states of consciousness by acting on brain receptors, notably serotonin receptors, and have minimal addictive cravings or intellectual impairment compared to other drugs.