The genes that predispose people to become addicted to alcohol could also play a part in cannabis dependence. Roughly 8-12% of cannabis users are considered to be dependent and, just like alcohol, the severity of symptoms increases with heavier use. A survey of Year 12 students in 2008 found that 5.4% of them had used cannabis daily in the last month. Researchers from Washington University School of Medicine studied 6,257 people in Australia. The participants in the study were all on the Australian twin registry and were made up of 2,761 pairs of twins and 735 singletons. The findings of the study showed that many of the same genetic factors that contributed to alcohol use also contributed to marijuana use and alcohol and cannabis dependence could also be traced to some of the same genetic influences.
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