The Journal of the American Medical Association (JAMA) reported on a study of 311 young adult twin pairs conducted by Michael T. Lynskey, PhD, in its Jan. 22, 2003 issue:

Individuals who used cannabis by age 17 years had odds of other drug use, alcohol dependence, and drug abuse/dependence that were 2.1 to 5.2 times higher than those of their co-twin, who did not use cannabis before age 17 years…

In particular, early access to and use of cannabis may reduce perceived barriers against the use of other illegal drugs and provide access to these drugs.

Jan. 22, 2003