Because of widespread use, understanding the pulmonary effects of cannabis use is important but its role independent from tobacco smoking is yet to be elucidated. We used Mendelian randomization (MR) to assess the effect of genetic liability to lifetime cannabis use and cannabis use disorder on pulmonary function and lung cancer.
We used four single nucleotide polymorphisms (SNPs) associated with lifetime cannabis use (p value <5×10) from a genome-wide association study (GWAS) of 184,765 individuals of European descent from the International Cannabis Consortium, 23andme and UK Biobank as instrumental variables. Seven SNPs (p value <5×10) were selected as instruments for cannabis use disorder from a GWAS meta-analysis of 17,068 European ancestry cases and 35,7219 controls of European descent from Psychiatric Genomics Consortium Substance Use Disorders working group, iPSYCH, and deCODE studies. The lung function GWAS included 79,055 study participants of the SpiroMeta Consortium, and a lung cancer GWAS from the International Lung Cancer Consortium (ILCCO) contained 29,266 cases and 56,450 controls.
MR showed that genetic liability to lifetime cannabis use was associated with increased risk of squamous cell carcinoma (OR = 1.22, 95% CI = 1.07-1.39; p value = 0.003; q value = 0.025). Pleiotropy-robust methods and positive and negative control analyses did not indicate bias in the primary analysis.
The findings of this MR analysis suggest evidence for a potential causal association between genetic liability for cannabis use and the risk of squamous cell carcinoma. Triangulating MR and observational studies, addressing orthogonal sources of bias, are necessary to confirm this finding.

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