LSD was introduced in psychiatry in the 1950s, and between 1960 and 1973 nearly 400 patients were treated with LSD in Denmark. By 1964, one homicide, two suicides, and four suicide attempts had been reported. In 1986, the Danish LSD Damages Law was passed after complaints by only one patient, and all 154 applicants received financial compensation for LSD-inflicted harm. Most patients suffered severe side effects many years afterward; two-thirds had flashbacks. With renewed interest in LSD therapy, the neurotoxic potential of LSD should be considered.
A retrospective database study of mental health patients who used LSD or psilocybin found that these drugs may be associated with serious short- and long-term side effects. The authors caution that until rigorous trials clarify the potential harms, the clinical utility of these substances in mental health patients remains unclear.
An analysis of medical records for 151 Danish psychiatric patients treated with LSD from 1960 to 1974 found no evidence of lasting personality changes like "connectedness." However, 2 to 4 patients showed other lasting personality changes, and many experienced unwanted effects persisting for weeks or months after acute treatment. In a reanalysis of a 1964 cohort, the same percentage of patients improved with LSD as in the original analysis, but side effects such as suicide attempts, suicides, and one homicide had received little attention. The authors conclude that future psychedelic research must respect the potential toxicity of LSD and meticulously monitor side effects.