May 13 (Bloomberg) -- Marijuana smokers who spend most of their time stoned are more likely to have higher levels of a protein that may raise risks of heart attack and stroke, scientists said.

The study subjects, who reported smoking from 78 to 350 joints a week, had elevated amounts of a chemical that raises the amount of fats in their blood, wrote researchers in the Journal of Molecular Psychiatry. Higher levels of these fats, known as triglycerides, increase risks of cardiac disease and stroke.

The study suggests marijuana's active ingredient stimulates the liver to produce too much of the protein. Marijuana is the most-frequently used illegal drug in the U.S., according to the National Institute on Drug Abuse. Heavy marijuana use has been linked to psychosis, hypertension and memory loss, the authors wrote.

``Evidence exists that its abuse is a risk factor for cardiovascular and cerebrovascular disorders,'' wrote the authors, whose research was led by Jean Lud Cadet of NIDA, based in Bethesda, Maryland.

The study, of 18 users and 24 non-smokers, wasn't designed to measure whether the pot-smokers had heart disease.

To contact the reporter on this story: Elizabeth Lopatto in New York at elopatto@bloomberg.net.

Last Updated: May 13, 2008 11:07 EDT