Which of the following would be classified as a hallucinogen?

PCP, or phencyclidine, is classified as a hallucinogen due to its effects on perception, mood, and thought processes. It alters an individual’s sensory perceptions, often leading to visual and auditory distortions, and even experiences of delusions or psychotic symptoms. These effects are characteristic of hallucinogens, which are substances that can create alterations in consciousness and perception.

In contrast, caffeine, alcohol, and nicotine are classified differently. Caffeine is a stimulant that mainly affects the central nervous system by increasing alertness. Alcohol is classified as a depressant, which slows down brain function and impairs cognitive and motor functions. Nicotine is a stimulant that primarily affects the body by increasing heart rate and alertness but does not produce hallucinations or alterations in sensory perception like PCP does. Therefore, PCP stands out as the only true hallucinogen among the options given.