Cannabis and psychosis: have we found the missing links?

BACKGROUND: The association between cannabis and psychosis has long been a matter of debate, with cannabis widely perceived as a harmless recreational drug. METHODS: Electronic bibliographic databases like PubMed and Google Scholar were searched using the format "(psychosis or schizophrenia or synonyms) and (cannabis or synonyms)". Cross-linked searches were made taking the lead from key articles. Recent articles and those exploring the genetic factors or gene-environment interaction between cannabis use and psychosis were focussed upon. RESULTS: Heavy cannabis use at a n young age, in association with genetic liability to psychosis and exposure to environmental stressors like childhood trauma and urban upbringing increases the risk of psychotic outcome in later life. CONCLUSION: Cannabis acts as a component cause of psychosis, that is, it increases the risk of psychosis in people with certain genetic or environmental vulnerabilities, though by itself, it is neither a sufficient nor a necessary cause of psychosis. Although significant progress has been made over the last few years, we are yet to find all the missing links. Further work is necessary to identify all the factors that underlie individual vulnerability to cannabis-related psychosis and to elucidate the biological mechanisms underlying this risk.