In an attempt to identify the factors responsible for adverse reactions to LSD and to elucidate the rising incidence of hospital admissions associated with use of the drug, the authors compared 25 psychiatric inpatients hospitalized following LSD ingestion with 25 members of a group who took LSD together regularly without reported difficulty. Although some differences were found between the groups, there were no outstanding historical or current clinical features which could be used to predict an individual's response to LSD with accuracy. These findings support the hypothesis that LSD interacts with schizoid trends, unsteady reality testing, and related factors in a complex way that makes accurate prediction of response virtually impossible.Abstract Teaser