There is a wide range of studies focusing on the use of cannabis in first episode psychosis (PEP). Literature using child and adolescent samples is scarce.

To determine the prevalence and clinical differences between cannabis users and non-cannabis users of early onset first episode psychosis (EOP), and adult onset first episode psychosis (AOP).

One hundred and forty patients were recruited in adult (AOP subsample, n = 69) and child and adolescent (EOP subsample, n = 71) mental health services. The Positive and Negative Syndrome Scale was used for psychotic symptoms and the Calgary Scale for affective symptoms. The Chi2 test analysed clinical differences between users and nonusers within subsamples, and in the total sample a Pearson correlation was used for the relationship between age at cannabis use and PEP.

The prevalence of lifetime use of cannabis and the average age at first use were 48% and 13.82 years (± 1.15) in the EOP subsample, and 58% and 17.78 years (± 3.93) in the AOP subsample. Within EOP, cannabis users were older (P = .001), had fewer negative symptoms (P = .045) and less depressive symptoms (P = .005). Within AOP, cannabis users were younger (P = .018) and had greater severity of positive symptoms (P = .021). Age at first cannabis use and age at PEP were positively correlated.

Cannabis use is prevalent in adult and early onset psychosis. Cannabis users differ clinically from non-users, and the earlier the use of cannabis, the earlier the onset of psychosis.

The authors have not supplied their declaration of competing interest.