title: Cannabis use and mania symptoms: a systematic review and meta-analysis.
abstract: BACKGROUND
  Whilst cannabis use appears to be a causal risk factor for the development of schizophrenia-related psychosis, associations with mania remain relatively unknown. This review aimed to examine the impact of cannabis use on the incidence of manic symptoms and on their occurrence in those with pre-existing bipolar disorder.
  
  
  METHODS
  A systematic review of the scientific literature using the PRISMA guidelines. PsychINFO, Cochrane, Scopus, Embase and MEDLINE databases were searched for prospective studies.
  
  
  RESULTS
  Six articles met inclusion criteria. These sampled 2391 individuals who had experienced mania symptoms. The mean length of follow up was 3.9 years. Studies support an association between cannabis use and the exacerbation of manic symptoms in those with previously diagnosed bipolar disorder. Furthermore, a meta-analysis of two studies suggests that cannabis use is associated with an approximately 3-fold (Odds Ratio: 2.97; 95% CI: 1.80-4.90) increased risk for the new onset of manic symptoms.
  
  
  CONCLUSIONS
  We were only able to identify a small number of studies of variable quality, thus our conclusions remain preliminary.
  
  
  CONCLUSIONS
  Our findings whilst tentative, suggest that cannabis use may worsen the occurrence of manic symptoms in those diagnosed with bipolar disorder, and may also act as a causal risk factor in the incidence of manic symptoms. This underscores the importance of discouraging cannabis use among youth and those with bipolar disorder to help prevent chronic psychiatric morbidity. More high quality prospective studies are required to fully elucidate how cannabis use may contribute to the development of mania over time.
authors.affiliation: Division of Mental Health and Wellbeing, Warwick Medical School, University of Warwick, CV4 7AL, UK.
authors.forename: Melanie
authors.initials: M
authors.lastname: Gibbs
authors.affiliation: Division of Mental Health and Wellbeing, Warwick Medical School, University of Warwick, CV4 7AL, UK.
authors.forename: Catherine
authors.initials: C
authors.lastname: Winsper
authors.affiliation: Division of Mental Health and Wellbeing, Warwick Medical School, University of Warwick, CV4 7AL, UK; Early Intervention Service, Swanswell Point, Coventry CV1 4FH, UK. Electronic address: s.marwaha@warwick.ac.uk.
authors.forename: Steven
authors.initials: S
authors.lastname: Marwaha
authors.affiliation: Caludon Centre, Coventry and Warwickshire Partnership Trust, CV2 2TE, UK.
authors.forename: Eleanor
authors.initials: E
authors.lastname: Gilbert
authors.affiliation: Warneford Hospital, University of Oxford, OX3 7JX, UK.
authors.forename: Matthew
authors.initials: M
authors.lastname: Broome
authors.affiliation: Division of Mental Health and Wellbeing, Warwick Medical School, University of Warwick, CV4 7AL, UK.
authors.forename: Swaran P
authors.initials: SP
authors.lastname: Singh
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001714:Bipolar Disorder / Q000139:chemically induced* / Q000523:psychology*; D002188:Cannabis / Q000009:adverse effects*; D006801:Humans; D008385:Marijuana Smoking / Q000523:psychology*; D008875:Middle Aged; D012307:Risk Factors; D055815:Young Adult
keywords: Bipolar; Cannabis; Mania; Meta-analysis; Systematic review