LSD is considered to be non-addictive with low potential for abuse.[19][20] Frequent use rapidly builds tolerance, requiring exponentially larger doses to feel an effect. Adverse psychological reactions are possible, such as anxiety, paranoia, and delusions.[7] It is possible for LSD to induce either intermittent or chronic visual hallucinations, in spite of no further use. Common effects include visual snow and palinopsia. In cases where this causes distress or impairment it is diagnosed as hallucinogen persisting perception disorder (HPPD).[21][22] While overdose from LSD is unknown, LSD can cause injury and death as a result of accidents stemming from psychological impairment.[15][11] The effects of LSD are thought to stem primarily from it being an agonist at the 5-HT2A receptor, and while exactly how LSD exerts its effects by agonism at this receptor is still not fully known, corresponding increased glutamatergic neurotransmission and reduced default mode network activity are thought to be key mechanisms of action.[20][7][11][23][24] In addition to serotonin, LSD also binds to dopamine D1 and D2 receptors, which is why LSD tends to be more stimulating than compounds such as psilocybin.[25][26] In pure form, LSD is clear or white in color, has no smell, and is crystalline.[12] It breaks down with exposure to ultraviolet light.[15]

LSD was first synthesized by Swiss chemist Albert Hofmann in 1938 from lysergic acid, a chemical derived from the hydrolysis of ergotamine, an alkaloid found in ergot, a fungus that infects grain.[15][21] LSD was one of various lysergamides Hofmann synthesized from lysergic acid while trying to develop a new analeptic. Hofmann discovered its effects in humans in 1943, after unintentionally ingesting an unknown amount, possibly absorbing it through his skin.[27][28][29] LSD was subject to exceptional interest within the field of psychiatry in the 1950s and early 1960s, with Sandoz distributing LSD to researchers under the trademark name Delysid in an attempt to find a marketable use for it