Comparing 25 people hospitalized after taking LSD with 25 regular users who had no reported difficulties, the study found no clear historical or clinical features that could reliably predict who would have an adverse reaction. The authors suggest that LSD interacts with personality traits such as schizoid tendencies and unstable reality testing in a complex manner, making accurate prediction of individual responses nearly impossible.
A survey of psychiatrists, psychiatric residents, internists, general practitioners, and psychologists in Los Angeles County counted over 2,000 patients with adverse LSD reactions seen during an 18-month period, which the authors consider a conservative estimate. Despite many clinicians' belief that such reactions were declining, the data show a substantial increase in reported cases from the first six-month period to the third.