A study of Australian twins and marijuana bolsters the fiercely debated “gateway theory” that pot can lead to harder drugs.
The researchers located 311 sets of same-sex twins in which only one twin had smoked marijuana before age 17. Early marijuana smokers were found to be up to five times more likely than their twins to move on to harder drugs.
They were about twice as likely to use opiates, which include heroin, and five times more likely to use hallucinogens, which include LSD.
Earlier studies on whether marijuana is a gateway drug reached conflicting conclusions. The impasse has complicated the debate over medical marijuana and decriminalization of pot.
Because this study involved twins, the findings would suggest that genetics play a subordinate role in drug use.
The study appears in Wednesday’s Journal of the American Medical Association and was funded in part by the National Institutes of Health.
It does not answer how marijuana, or cannabis, might lead to harder drugs.
