Hallucinogens are mind-altering drugs that cause hallucinations and distort experience while blurring the boundaries between reality and fantasy. Natural or synthetic: natural: mushrooms, synthetic: lsd. Users may speak of seeing sounds and hearing colours or other mythical experiences/insights. Can lead to violent outbursts and paranoia/panic. The effects of hallucinogens are unpredictable and that is their greatest danger. Marijuana is classified by some as a stimulant, by some as a sedative, and some believe it belongs in its own category. Causes mild euphoria, relaxation, enhanced sensory experience, increase appetite, impaired memory and relaxation time. Thc is marijuana"s most active ingredient: binds to receptors on neurons throughout brain, brain produces own thc like substances called cannabinoids. May increase gaba (slows neural activity relaxation) Animal research indicates genetic factors influence sensitivity and tolerance. Identical twins have higher concordance rate for alcoholism than fraternal twins.