Which of the following is not classified as a hallucinogen?

THC, or tetrahydrocannabinol, is the main psychoactive compound found in cannabis. While THC can produce alterations in perception, mood, and cognition, it does not fit the traditional definition of a hallucinogen. Hallucinogens are typically characterized by their ability to significantly distort perception, leading to visual or auditory hallucinations, altered sensory experiences, and profound changes in thought processes.

In contrast, MDMA, STP, and MDA are all substances that are classified as hallucinogens due to their effects on the serotonin receptors in the brain, leading to alterations in perception and sensory experiences. MDMA, often known as ecstasy, induces feelings of euphoria and enhanced sensory perception, while STP (serotonin-2,5-dimethoxy-4-methylamphetamine) and MDA (3,4-methylenedioxyamphetamine) share similar hallucinogenic properties. This makes THC distinct in its classification, as it is often categorized more accurately as a cannabinoid rather than a traditional hallucinogen.