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July 16, 2003

Early Exposure to Marijuana and Risk of Later Drug Use

Author Affiliations

Letters Section Editor: Stephen J. Lurie, MD, PhD, Senior Editor.

JAMA. 2003;290(3):329. doi:10.1001/jama.290.3.329-a

To the Editor: Dr Lynskey and colleagues1 concluded that early cannabis use is associated with an increased risk for later use and dependence on other drugs. Although the authors used both monozygotic and dizygotic same-sex twins to ensure similar environmental influences, we are concerned that the sample may not be representative of the population, as there was an unusually high prevalence of alcohol dependence in both cannabis users and their co-twin controls compared with that of the general population.2,3 Early cannabis users in the study of Lynskey et al had a 42.8% prevalence of alcohol dependence, whereas their co-twin controls had a prevalence of 29.6%. By contrast, the prevalence of alcohol abuse among Australian adults has been reported to be about 6.5%,2,4 with a 4.1% prevalence of alcohol dependence.2 About 8.3% of Australians aged 14 years and older report daily alcohol use.5 Similarly, the prevalence of alcohol dependence in the United States has been estimated to be about 6% of men and 2% of women.3