LSD is a synthetic hallucinogenic drug discovered in 1938 that was widely experimented with and used recreationally in the 1960s but is now illegal; it produces vivid visual hallucinations and alters thinking when taken in doses of 100-200 micrograms but can also cause anxiety, paranoia, and flashbacks, with rare potential long-term psychological risks if used heavily or by those with mental illness. Harm reduction principles for guiding someone on an LSD trip focus on creating a safe environment without interference while talking through the experience afterwards.