Aims: We sought to estimate the contribution of genetic and environmental factors to adolescent tobacco, alcohol and other substance use.
Design, setting and participants: The sample consisted of 327 monozygotic and 174 like-sex dizygotic twin pairs born in Minnesota and aged 17-18 years at time of assessment. Biometrical methods were used to estimate the contribution of additive genetic, shared and non-shared environmental factors to adolescent substance use.
Measurements: As part of a day-long psychological assessment, adolescent twins completed a computerized substance use interview to determine whether they had ever used tobacco, alcohol or other illicit drugs.
Findings: The heritability for the liabilities to tobacco, alcohol and other drug use was estimated to be 59%, 60% and 33% among males, and 11%, 10% and 11% among females. However, the gender difference was not statistically significant. Estimates of shared environmental effect were substantial and insignificantly higher among females (71%, 68% and 36%, respectively) than among males (18%, 23% and 23%, respectively). The covariation among the three substance use phenotypes could be accounted for by a common underlying substance use factor. Estimates of the contributions of genetic, shared environmental and non-shared environmental factors to variance in this factor were 23% 63% and 14%, respectively.
Conclusions: These findings add to the growing behavioral genetic literature indicating that adolescent initiation of substance use, a powerful predictor of adult substance use diagnosis, is influenced primarily by environmental rather than genetic factors.