Early Drinking Initiation and Illicit Drug Use / Join Together, 11 July 2008
http://www.jointogether.org/news/research/summaries/2008/early-drinking-illicit-drug.html
"The earlier a person begins drinking alcohol, the more likely they are to have ever used other drugs illicitly, according to an analysis of data from the National Longitudinal Alcohol Epidemiologic Survey (NLAES). Approximately one-half of persons who began drinking at age 14 or younger had also used other drugs illicitly in their lifetime, compared to around one-tenth of those who began drinking at age 20 or older."
PDF - http://www.cesar.umd.edu/cesar/cesarfax/vol17/17-26.pdf