LSD (lysergic acid diethylamide) is one of the major drugs making up the hallucinogen class of drugs. Hallucinogens cause hallucinations—profound distortions in a person’s perception of reality. The effects of LSD are unpredictable. Some LSD users experience severe, terrifying thoughts and feelings, fear of losing control, fear of insanity and death, and despair while using LSD. Some fatal accidents have occurred during states of LSD intoxication.