A twin study of drinking and smoking onset and latencies from first use to regular use.

The early onset of alcohol and tobacco use has been associated with increased risk for later substance abuse and dependence problems. This study investigated genetic and environmental influences on age at onset of alcohol and tobacco use by examining twin resemblance for several retrospectively reported onset milestones including age at first use, age at first alcohol intoxication experience, and age at regular use. In addition, we also examined the latency between age at first use and age at regular use of tobacco and alcohol. The subjects were a volunteer sample of older adult twins 50 to 96 years of age. MZ twin correlations for age at first alcohol use and age at first tobacco use were .57 and .44, respectively, compared to .45 and .37 for DZ same-sex twins. MZ twins correlated .30 and .26 for the latencies between first use and regular use of alcohol and of tobacco, while DZ correlations were -.01 and .05, respectively. Biometrical model-fitting results confirmed that familial resemblance for age at first use for both alcohol and tobacco was largely the result of shared environmental factors, while the latencies between first use and regular patterns of use were more genetically influenced. These findings add to a growing body of literature suggesting that initiation of substance use is influenced primarily by environmental rather than genetic factors.