In the popular mythology, LSD users are prone to violent outbursts and bizarre, sometimes violent, behavior. The literature on LSD does document some bizarre episodes but, given the millions of doses that have been consumed since the 1950s, these are rare. The medical literature is valuable in documenting the occurrence of adverse consequences attributed to LSD use and is a good indicator of which adverse effects are common and which are infrequent. By far the most common adverse reaction to LSD is a bad trip, an acute anxiety or panic reaction following ingestion of the drug. Prolonged psychiatric illness appears to be a rare complication of LSD use; if large numbers of such cases exist, they are not documented in the scientific literature. LSD as a cause of suicide is difficult to evaluate, but probably infrequent. A few homicides are alleged to have been committed by persons under the influence of LSD. Aggression is not a common response to LSD, however, and the involvement of other drugs and prior psychiatric illness appear to have been contributing factors. LSD appears to pose few if any risks to physical health. Long-term chronic abuse of LSD rarely develops. Although LSD can induce chromosome breaks both in laboratory cell cultures and in the circulating blood cells of LSD users, it has no lasting effect on genes or chromosomes. Notes