What defines hallucinogens?

Hallucinogens are characterized by their ability to significantly alter an individual's perception of reality. This includes changes in sensory perception, mood, and cognitive processes. When ingested, these substances can lead to vivid visual and auditory hallucinations, causing the user to experience the world in a way that deviates from normal perception. This alteration can affect how the individual interprets their surroundings, leading to profound and sometimes life-altering experiences.

The other options describe effects related to different categories of substances. For instance, substances that slow down brain activity are typically classified as depressants, while those that increase appetite can be related to specific medicinal uses or recreational drugs that stimulate hunger. Similarly, substances that decrease anxiety often belong to categories like anxiolytics or sedatives, but they do not inherently involve changes to perception. Therefore, the defining characteristic of hallucinogens lies in their unique ability to distort reality, making them distinct from other types of psychoactive substances.