Which of the following is an example of a hallucinogen?

LSD, or lysergic acid diethylamide, is classified as a hallucinogen because it primarily alters a person’s perception, mood, and various cognitive processes. This drug can induce vivid hallucinatory experiences, affecting the individual's visual and auditory senses, leading to a distorted sense of reality. Users often report dramatic changes in perception, including visual distortions and altered thinking.

In contrast, the other substances mentioned do not fall under the hallucinogen category. Crystal meth is a powerful stimulant that increases energy and alertness. GHB is primarily known as a depressant and is often associated with sedative effects. Xanax is a benzodiazepine, typically used to treat anxiety and panic disorders, functioning as a central nervous system depressant. These differences in the primary effects and mechanisms of action of these drugs clarify why LSD stands out as a hallucinogen.