DNA methylation profiles of long-term cannabis users in midlife: a comprehensive evaluation of published cannabis-associated methylation markers in a representative cohort.

Epigenetic responses to cannabis use could link cannabis use to health problems. We examined the DNA-methylation profiles of long-term cannabis users in midlife, re-evaluating a set of 246 cannabis-associated methylation markers that were previously identified in other studies. Data were from the Dunedin Study, a five-decade longitudinal study of a birth cohort (analytic n = 787). Peripheral whole blood was drawn when the cohort was age 45, and DNA methylation was assayed using the EPIC 850 K BeadChip. Analyses compared long-term cannabis users with non-users and, for a benchmark comparison, long-term tobacco users. Results showed that long-term cannabis use was associated with sixteen of the previously published 246 cannabis-related methylation markers. Methylation markers that were associated with long-term cannabis use were also associated with long-term tobacco use. However, after adjusting for long-term tobacco use and other covariates, long-term cannabis use was robustly associated with hypomethylation of nine markers: cg05575921, cg21566642, cg03636183, cg21161138, cg01940273, cg17739917, cg05086879, cg02978227, cg23079012. Cannabis-related hypomethylation was associated with higher gene expression in the Dunedin Cohort, suggesting meaningful biological associations. A comparison of long-term cannabis users with cannabis quitters revealed that quitters showed less extreme DNA hypomethylation. Long-term cannabis use could affect the epigenome similarly to tobacco use, possibly at least partly though smoke inhalation. Cannabis cessation, like tobacco cessation, may reverse altered DNA methylation.