Rats supporting conservatives, again

news @ nature.com-Rats taking cannabis get taste for heroin-Study suggests cannabis-users may be vulnerable to harder drugs.

Here we go again. Nothing terribly conclusive about the above work, but yet again a case of drug research seemingly coming round to validate old fuddy-duddy conservative's long held suspicions about marijuana:

Neuroscientists 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, Sweden, who carried out the study.

I note that one site criticises the report, but on some fairly spurious grounds:

But the article did not note that the problem with the “gateway theory” is that the vast majority of cannabis users never try harder drugs. While most illegal drug users start with the most widely available illegal drug — marijuana — most marijuana users start and stop with cannabis. Some 50 percent of high school students try marijuana before graduation, but just eight percent try cocaine, six percent try methamphetamine and less than one percent try heroin. This is why the Institute of Medicine, in a 1999 report on the use of marijuana as medicine, gave no credence to the gateway idea.

In fact, the news@nature report does talk about the role of social issues when you talk of "gateway drug". The point of the study was clearly stated as this:

There has long been a debate about whether exposure to drugs such as nicotine or marijuana might lead to harder habits. Many argue that the most important factors in the equation are social ones: people who get one drug from a dealer are probably more inclined to try another. But researchers are still interested to know whether there is any physiological effect that might additionally predispose users of so-called soft drugs to harder-drug addiction.

Fair enough. Seems to me to not be too much point in being nitpicky about what exactly the "gateway theory" means, if studies do confirm use of cannibis means greater addiction to harder drugs if you try them. (Even if it is only social reasons as to why you have the opportunity to try them.)

UPDATE: Futurepundit's post on this story points out that it should be no surprise. Early alcohol use is a clearly related to increased alcoholism in future too:

In results that echo earlier studies, of those individuals who began drinking before age 14, 47 percent experienced dependence at some point, vs. 9 percent of those who began drinking at age 21 or older. In general, each additional year earlier than 21 that a respondent began to drink, the greater the odds that he or she would develop alcohol dependence at some point in life. While one quarter of all drinkers in the survey started drinking by age 16, nearly half (46 percent) of drinkers who developed alcohol dependence began drinking at age 16 or younger.