Lysergic acid diethylamide, commonly known as LSD (from German Lysergsaeure-diethylamid), also known colloquially as acid, is a potent psychedelic drug.

Effects typically include intensified thoughts, emotions, and sensory perception. At sufficiently high dosages LSD manifests primarily mental, visual, as well as auditory, hallucinations. Dilated pupils, increased blood pressure, and increased body temperature are typical.