Letters Section Editor: Stephen J. Lurie,
MD, PhD, Senior Editor.
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
Schier JG, Nelson LS, Hoffman RS. Early Exposure to Marijuana and Risk of Later Drug Use. JAMA. 2003;290(3):329. doi:10.1001/jama.290.3.329-a
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