Effects of cannabis use on physical health using a co-twin control design

Abstract Background Research on the influence of cannabis use on anthropometrics, cardiovascular and pulmonary functioning, and other indicators of physical health has reported mixed results. We examined whether cannabis frequency is associated with physical health outcomes phenotypically and after controlling for shared genetic and environmental factors via a longitudinal co-twin control design. Methods We tested the phenotypic associations of adolescent, young adult, and adult cannabis frequency with adult physical health. Next, we ran multilevel models to test if significant phenotypic associations remained at the between-family and within-twin pairs levels. Participants include 677 individual twins (308 twin pairs) aged 20-35. Results At the phenotypic level, adolescent cannabis use was associated with less adult exercise engagement (b=-0.846 minutes, p=.000). Adult cannabis use was associated with a lower heart rate (HR; b=-0.170 bpm, p=.001) and more frequent appetite loss (b=0.018, p=.000). Only between-family effects were significant for adolescent cannabis use and exercise engagement (b=-1.147 minutes, p=.000) and adult cannabis use and appetite loss frequency (b=0.041, p=.002). The total within-twin (b=-0.184, p=.014), MZ only (b=-0.304, p=.003), and between-family effects (b=-0.164, p=.025) were significant between adult cannabis use and a lower HR, which persisted after controlling for familial confounds and other substance use. Conclusions The associations between cannabis use with exercise engagement and frequency of appetite loss are explained by familial confounding while the association between cannabis use and resting HR was not. These results do not support a causal association between cannabis use once a week and poorer physical health effects among adults aged 20-35.