It is important to note that to date, most research has focused on the onset of alcohol use. The onset of drug use and the interaction between the onset of alcohol and drug use on later substance use has been relatively neglected. However, some research18 indicates that adolescents who use both alcohol and other drugs (e.g., marijuana) are at a greater risk for alcohol problems than those who use alcohol alone. Moreover, there is evidence for a common liability such that age of onset of alcohol and marijuana both may predict later alcohol use problems.19
