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Abstract
The use of cannabis has previously been linked to both depression and self-harm; however, the role of genetics in this relationship is unclear. This study aimed to test for evidence of genetic associations between cannabis use and depression and self-harm.
We used UK Biobank data to test the phenotypic association between lifetime measures of cannabis use, depression and self-harm. We then combined the UK Biobank genetic data with summary statistics from other datasets to further test the genetic relationships between these traits using three different methods: LD score regression, polygenic risk scoring and Mendelian randomization methods.
We found that in UK Biobank, cannabis use is associated with an increased likelihood of depression and self-harm. The strength of this phenotypic association is stronger when more severe trait definitions of cannabis use and depression are considered. Using UK Biobank data together with other data sources, we found evidence of significant genetic relationships between cannabis use, depression and self-harm. However, limitations in statistical power mean that conclusions could not be made on the direction of causality between these traits.