Heavy marijuana use can boost blood levels of a particular protein, perhaps raising a person's risk of a heart attack or stroke, U.S. government researchers said yesterday.

Dr. Jean Lud Cadet of the National Institute on Drug Abuse, part of the National Institutes of Health, said the findings point to another example of long-term harm from marijuana. But marijuana activists expressed doubt about the findings.

Cadet said a lot of previous research has focused on the effects of marijuana on the brain. His team looked elsewhere in the body, measuring blood protein levels in 18 long-term, heavy marijuana users and 24 other people who did not use the drug.

Levels of a protein called apolipoprotein C-III were found to be 30 per cent higher in the marijuana users compared to the others. This protein is involved in the body's metabolism of triglycerides and higher levels cause increased levels of triglycerides, Cadet added.