Firth models supported effect directions but were underpowered.<h4>Conclusions</h4>HLA class II immunogenetic background may modify psychosis risk among cannabis users: DRB5/DRB1*16-containing backgrounds were associated with increased vulnerability, whereas DRB4/DRB3 paralogs were associated with reduced schizophrenia risk in this cohort. This evidence concerns the gene HLA-DRB5 and schizophrenia.