The document discusses the classification and mechanisms of action of various recreational drugs commonly used on US campuses including alcohol, nicotine, caffeine, and THC. It notes that alcohol acts as a CNS depressant by stimulating GABA and altering serotonin and dopamine. Nicotine and caffeine act as CNS stimulants in different doses by affecting neurotransmitters like norepinephrine. THC acts as a hallucinogen through partial agonist activity at cannabinoid receptors in the brain. Around 55% of college students report alcohol use. Government agencies like NIAAA monitor substance use amongst college students. Long term use and abuse can lead to health issues like cancer, strokes, and addiction.