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Cannabis - the gateway to heroin abuse

Stockholm, Sweden, February 9, 2007

Drugnews, a Scandinavian news agency on the Internet, has previously reported on the research that neuroscientist Maria Ellgren has been doing on rats. Today she presents her doctor’s dissertation "Neurobiological Effects of Early Life Cannabis Exposure in Relation to the Gateway Hypothesis" at Karolinska Institutet in Stockholm. Several epidemiological studies support the so called stepping stone theory – misuse of hashish or marijuana can later in life leads to misuse of other narcotic drugs. This is supported by the fact that the majority of drug addicts started off with cannabis. But the theory is disputed, mostly by those that think that experimenting with cannabis is not a very serious thing.

Maria Ellgren wanted to find out if it is the cannabis exposure in itself or social and/or genetic factors that constitute the gateway to other drugs. - We wanted to test the stepping stone theory, excluding social and moral factors. All drugs which can lead to addiction affect the system of reward in the brain and the question therefore is whether the exposure of cannabis to the brain causes molecular and neurochemical changes that lead to an increased reward-effect from other drugs, says Maria Ellgren at the Institution for Clinical Neuroscience of Karolinska Institutet.

One group of rats in their "teens" was given low doses of cannabis in their drinking water regularly. Another group was given salted water. After a time of abstinence when the groups had reached mature age the rats were exposed to heroin with no limitations. Those rats that had been given cannabis took much more heroin than those that had been served salted water. The experiment also showed that the cannabis rats had changes in their brains, in the areas which are strongly connected to feelings of reward and well being. These changes were not observed in the control group.

Similar experiments with pregnant rats showed that those rats that had been exposed to cannabis before birth would be more apt to take heroin in adult age. However the study does not show any link between early cannabis exposure and later sensitivity to central stimulant drugs, such as amphetamine, which Ellgren points at as another interesting find.

The Swedish National Coordinator of Drugs Policy (drugczar) Bjorn Fries, says in a comment that the research of Maria Ellgren is very interesting. - It is of vital importance that we can get scientific support for the links between cannabis and other drugs. These links cannot be rejected as myths or political statements, says Bjorn Fries in a comment to Svenska Dagbladet, the second largest morning paper in Sweden.

Reported by Sven Liljesson/www.drugnews.se

Translated by Per Johansson/RNS