Increased psychotomimetic response to cannabis is demonstrated in psychosis-prone individuals. Early use of cannabis has poorer prognostic outcomes. However, as yet no cut-off age for early use has been established.

To determine, if age at first use affects later cannabis experiences and to determine if a “critical age” of first use exists for psychotomimetic cannabis experiences.

The cannabis experiences questionnaire (CEQ) (EUGEI version) was administered to a large internet-based non-clinical sample. Regression analysis was conducted of age at first use against CEQ scores controlling for gender, age frequency of use and duration of use. To determine cut-off age: independent ‘t’ tests (parametric) and Mann–Whitney-U tests (non-parametric) were used to determine significance of differences in CEQ scores at cut-off ages from 12-25.

We obtained data for 1115 participants. Younger age at first use was significantly associated with increased psychotomimetic experiences (adjusted P < 0.001). All cannabis experiences were increased in in those commencing at younger age at every cut off age from 17 to 22 (P < 0.001) with maximal difference at 22. Psychotic experiences significantly varied from age of first use of 19 to 22 with maximal difference at cut-off ages 20, 21 and 22 (P < 0.001). Pleasurable experiences were significantly reduced in those commencing later at every cut-off age from age of use 17 to 22 (P < 0.001) with maximal difference between groups at age 20.

Later onset of use is associated with reduced cannabis experiences till the early 1920s. This may have public health implications.

The authors have not supplied their declaration of competing interest.