Which substance is NOT considered a hallucinogen from the provided list?

Aspirin is the substance that is not considered a hallucinogen because it is a non-steroidal anti-inflammatory drug (NSAID) primarily used to relieve pain, reduce inflammation, and lower fever. Unlike hallucinogens, which alter perception, mood, and cognitive processes, aspirin does not induce hallucinations or significantly change sensory experiences.

In contrast, PCP, DXM, and ketamine are all classified as hallucinogens. PCP (phencyclidine) is known for its dissociative effects and can lead to experiences of detachment from the environment. DXM (dextromethorphan) is often found in cough syrups and can cause hallucinogenic effects at high doses. Ketamine, commonly used as an anesthetic, is also recognized for its hallucinogenic properties, particularly in recreational contexts. Each of these substances can alter perception and cognition, which distinguishes them from aspirin.