Age at initiation of amphetamine use and age at onset of psychosis: the Australian Survey of High Impact Psychosis.

Individuals with a psychotic disorder who had a premorbid history of amphetamine use (n=382) were analyzed in groups according to age of initiation to amphetamine (AIA) and mean number of years of duration of premorbid exposure to amphetamine (DPEA) was calculated. Univariate General Linear Models were used to test for group differences in age at onset of psychotic illness (AOI) and DPEA. Although a temporal direct relationship between AIA and AOI was detected (mean duration 5.3 years), our findings suggested this association was spurious and better explained by a later initiation to amphetamine than to cannabis (by 2-3 years).