New twin study out of the US suggests that the same gene that leads to drinking alcohol may also lead to marijuana use.
Twin studies are used to better understand the genetic influence of behaviours. In such studies, scientists compare the results from identical twin sets, who have identical genetics, with the results from fraternal twin sets, who only share some genes.
The new study looked at 2,761 sets of identical and fraternal twins, as well as 736 non-twin individuals, from 24 to 36 years of age. All subjects were interviewed about their alcohol and marijuana use.
Although researchers found little overlap between the environmental factors that influence use, they found significant overlap in the genetic factors that influence.
In previous twin studies, about 50 to 60 percent of the variance in alcohol dependence could be explained by genetic factors. Studies also previously suggested that genetics played a major role in marijuana and other drug addictions.
However, this new study found that over 60 percent of the variance in alcohol and marijuana use, and marijuana dependence, was linked to genetic factors, supporting the theory that common genes play a role in all addiction & substance abuse.
The results are to be published in Alcoholism: Clinical and Experimental Research March 2010.
Source: WebMD