Hallucinogenic drugs are substances that alter a person's perception, causing them to experience hallucinations or distorted sensory experiences. These drugs can produce vivid and complex visual, auditory, or other sensory experiences that have no external reality. Examples of hallucinogens include LSD, psilocybin (found in magic mushrooms), mescaline (found in peyote cactus), and DMT (a naturally occurring psychedelic substance).