Regarding sex differences in substance use, males tend to use more substances than females (e.g., 1–3). Estimates of genetic and environmental influences on individual differences in substance use appear to differ by sex in mixed-age samples. In adolescent samples, genetic factors tend to account for a greater proportion of the variance in males (around one-third) than in females (around one-quarter), although these differences do not always end up being statistically significant (e.g., 8, 13).
