Original Article Cannabis use in first-treatment bipolar I disorder: relations to clinical characteristics Levi R. Kvitland, 1 Ingrid Melle, 1 Sofie R. Aminoff, 2 Trine V. Lagerberg, 1 Ole A. Andreassen 1 and Petter A. Ringen 3 1 NORMENT, KG Jebsen Centre for Psychosis Research, Division of Mental Health and Addiction, Oslo University Hospital and Institute of Clinical Medicine, University of Oslo, 3 Division of Mental Health and Addiction, Oslo University Hospital, Oslo, and 2 Division of Mental Health Services, Akershus University Hospital, Lørenskog, Norway Corresponding author: Mr Levi R. Kvitland, NORMENT, KG Jebsen Centre for Psychosis Research, Division of Mental Health and Addiction, Oslo University Hospital and Institute of Clinical Medicine, University of Oslo, N-0424 Oslo, Norway. Email: l.r.kvitland@medisin.uio.no Received 5 November 2013; accepted 28 February 2014 Abstract Aims: The aim of this study was to investigate the associations between recent cannabis use, current symp- tomatology and age at onset of first manic, depressive and psychotic epi- sodes in a large sample with first- treatment bipolar I disorder (BD I). Methods: One hundred one patients with first-treatment Diagnostic and Statistical Manual of Mental Disor- ders, Fourth Edition (DSM-IV) bipolar I disorder were included as part of the Thematically Organized Psycho- sis study. The Structural Clinical Interview for DSM-IV was used for DSM-IV diagnosis and identification of episodes of illness. Earlier suicide attempts were recorded. Manic, depressive and psychotic symptoms were rated using the Young Mania Rating Scale, Inventory of Depressive Symptoms and Positive and Negative Syndrome Scale correspondingly. Cannabis use within the six last months was recorded. Results: After controlling for con- founders, recent cannabis use was significantly associated with lower age at onset of first manic and psy- chotic episode, but not with onset of first depressive episode (both P < 0.05). Recent use was also associ- ated with more lifetime suicide attempts (P < 0.01). No group differ- ences were found on symptom levels. Conclusions: The present study con- firms earlier findings of an associa- tion between cannabis use and a lower age at onset. Recent cannabis use was also associated with more lifetime suicide attempts. The current findings suggest that recent cannabis use is associated with a more severe course of illness in the early phase of BD I. Key words: age at onset, bipolar I, cannabis, first treatment. INTRODUCTION Bipolar disorder (BD) ranks among the top 10 con- tributors to the global burden of disease. 1,2 Identify- ing risk factors associated with the onset of BD is as a key target for research. 3 However, few risk factors have been identified apart from a family history of bipolar disorder. 4 Cannabis use is prevalent in BD, 5,6 also before the start of first treatment. 7,8 The evi- dence for cannabis as a risk factor in BD is weaker than for schizophrenia, 9 but recent research, includ- ing studies of large epidemiological and clinical samples from the United States and Europe, clearly indicate an effect of cannabis in lowering the age at onset across age cohorts. 10,11 Cannabis use has further been shown to increase the risk for mania, prolong the duration of manic episodes 10–12 and increase suicide risk. Cannabis use also seems to increase the risk for developing BD in depressed individuals. 13 However, previous studies showing an effect of cannabis on age at onset mainly comprise multi- episode patients. This makes it difficult to rule out the alternative explanation, for instance, that the more severe course seen in early-onset patients could increase the risk for cannabis use after onset or in other ways interacts with negative effects of cannabis use in this time period. Study samples with longer duration of illness are also more vulner- able to attrition bias and thus potentially less representative of the BD patient population than first-treatment samples. Furthermore, these Early Intervention in Psychiatry 2016; 10: 36–44 doi:10.1111/eip.12138 First Impact Factor released in June 2010 and now listed in MEDLINE! © 2014 Wiley Publishing Asia Pty Ltd 36