Dr. Peter Libby, chief of cardiovascular medicine at Boston's says that it would be premature to think that "a joint a day will keep the doctor away". Libby, who did not participate in the study, said the work was valuable for identifying the CB2 receptor as a potential target for treatment in hardening of the arteries, and showing that a natural substance could help.

Hardening of the arteries is the initial stage for many heart attacks and inflammation plays a critical role in the condition, indicated by a progressive buildup on the inside walls of blood vessels. The Swiss team explored the anti-inflammatory effects of marijuana's main active ingredient, Delta 9 tetrahydrocannabinol, or THC.

They fed mice a high-cholesterol diet for 11 weeks and halfway through that period, some of the mice were given very low, daily oral doses of THC -- too low to produce any marijuana-like changes in behaviour. At the end of the experiment, mice that had been given the THC had a lower level of blood vessel clogging than the others.

The THC had a beneficial effect on the immune-system cells and reduced their secretion of an inflammation-promoting substance and their migration to the vessel wall.

It did that by binding to proteins called CB2 receptors, which are found mostly on immune-system cells. THC also targets CB1 receptors, found mostly in the brain.

Scientists,Mach suggests, should try to develop a drug that works on CB2 receptors while ignoring the brain receptors.

Related work has shown no additional benefit from higher THC doses, such as a person would get from smoking marijuana, controlling one's weight, exercising and healthy eating have already been proven to reduce a person's risk of heart attacks and strokes from clogged arteries. Dr Mach believes future work will focus on finding drugs that mimic the benefit without producing marijuana's effects on the brain.

Dr. Edward A. Fisher of the New York University School of Medicine said THC's impact on artery-clogging in the experiment was relatively modest, and it is not clear that results would apply.

The research is published in the current issue of the journal Nature.