Close window Published online: 5 July 2006; | doi:10.1038/news060703-9 Rats taking cannabis get taste for heroinStudy suggests cannabis-users may be vulnerable to harder drugs.Michael HopkinNeuroscientists have found that rats are more likely to get hooked on heroin if they have previously been given cannabis. The studies suggest a biological mechanism — at least in rats — for the much-publicized effect of cannabis as a 'gateway' to harder drugs. The discovery hints that the brain system that produces pleasurable sensations when exposed to heroin may be 'primed' by earlier exposure to cannabis, say researchers at the Karolinska Institute in Stockholm,...