Marijuana at a young age opens door to drug dependence
31 January 2003
People who begin smoking marijuana before 17 years of age are 2 to 5 times more likely to develop an alcohol or drug dependence in later life, an Australian study has found.
Australian and US researchers studying 311 same-sex, fraternal or identical twin pairs found that early cannabis use increased the risk of other drug abuse and dependence, even when known risk factors were taken into account.
These known risk factors include early-onset alcohol or tobacco use, parental conflict or separation, childhood sexual abuse, conduct disorders, major depression and social anxiety (Journal of the American Medical Association 2003; 289: 427-33).
(Fraternal or 'dizygotic' twins are the result of 2 eggs being fertilised at the same time; whereas identical or 'monozygotic' twins are the result of one egg being fertilised and soon after dividing to form 2 embryos.)
People who used cannabis before they were 17 had a 2.3 to 3.9-fold increase in the odds of other drug use, and a 1.6 to 6.0-fold increase in the odds of alcohol dependence and other drug abuse/dependence compared with their twin who had not used cannabis before age 17. This was regardless of whether the pair was monozygotic.
The association could not be explained by common predisposing genetic or shared environmental factors, so researchers suggested it might be due to the effects of the peer and social context in which cannabis was used and obtained.
Last Reviewed: 30 January 2003
- 1. Medical Observer Weekly 31/01/03
