Which one of the following substances is categorized as a hallucinogen?

LSD, or lysergic acid diethylamide, is classified as a hallucinogen because it primarily alters perception, mood, and various cognitive processes. Hallucinogens are substances that can induce hallucinations—sensory experiences that appear real but are created by the mind. LSD is notorious for producing profound changes in thought processes and visual and auditory distortions, often leading to an altered state of consciousness.

In contrast, other substances listed, such as alcohol and cocaine, do not produce these types of perceptual changes characteristic of hallucinogens. Alcohol is a depressant that primarily affects the nervous system, leading to slowed functions and impaired judgment. Marijuana can induce some altered states of perception but is generally categorized as a psychoactive substance rather than a hallucinogen, although some users may experience mild hallucinations at high doses. Cocaine is a stimulant that increases energy and alertness but does not typically cause hallucinations. Therefore, LSD stands out distinctly in its classification as a hallucinogen, given its specific effects on perception and consciousness.