THE active ingredient in cannabis protects arteries against harmful changes that lead to strokes and heart attacks, new research suggests.

THC, or delta-9-tetrahydrocannabinol, is known to affect the brain and make cannabis-users “high”. The new research shows that it also has an influence on blood vessels.

A study of mice revealed that the compound blocks the process of inflammation, which is largely responsible for the narrowing of arteries.

Inflammation combines with fatty deposits to produce obstructive “plaques”, a condition known as atherosclerosis. These can block arteries to the heart, causing angina and heart attacks, or to the brain, leading to strokes. Atherosclerosis is the primary cause of heart disease and stroke in the Western world, accounting for up to half the deaths from both conditions.

The scientists, led by François Mach, from Geneva University Hospital in Switzerland, studied a strain of specially bred mice that are susceptible to narrowing of the arteries. They were fed a high-cholesterol diet to make them develop atherosclerotic plaques. Adding THC to their diet caused the growth of the obstructions in their arteries to slow markedly after 11 months. When the mice were given a chemical that blocked the action of THC, their arteries continued to narrow at a fast rate.

Writing in Nature, the scientists point out that the THC doses used were low — too low to cause the mice to get “high”. They wrote: “Our results suggest that cannabinoid derivatives with activity at the CB2 receptor may be valuable clinical targets for treating atherosclerosis.”

Michael Roth, an American critical-care expert from the University of California at Los Angeles, urged caution when considering cannabis as a heart disease therapy.

“The findings. . . are striking, but they should not be taken to mean that smoking marijuana is beneficial to the heart,” Professor Roth wrote in an accompanying article. “The dose response curve to THC in this study was very narrow and U-shaped, with higher and lower concentrations failing to produce protective effects.

“It would be difficult to achieve such specific concentrations in the blood by smoking marijuana. Also, no studies have been performed in humans to evaluate the effects of THC on atherosclerosis.”

He added that the effects of THC on the brain, where it binds to a different receptor protein, could counteract its benefit to the heart.

THE DOPE ON MARIJUANA

Present-day cannabis, the result of selective breeding, is reckoned to be more potent than that smoked by the flower-power generation

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