Slowed reflexes, decreased libido, memory loss, the munchies. Add to that list another side effect of smoking marijuana — changes in blood chemistry that could increase the risk of heart disease.
Habitual marijuana use increases the blood levels of a protein that has been implicated in heart disease, according to new research in the May Molecular Psychiatry. Down the line, that could mean increased incidence of stroke and heart attack for frequent marijuana users.
The study looked at 18 chronic marijuana users and 24 matched volunteers who did not smoke weed. The heavy users, who were mostly in their early 20s, otherwise healthy and used no other drugs, reported smoking anywhere from 78 to a whopping 350 joints per week. “Basically, that’s what they did all day long,” says Jean Lud Cadet of the National Institute on Drug Abuse in Bethesda, Md.
Cadet and his colleagues took blood samples from each group
and tested for the presence of multiple disease markers. Those who regularly
got stoned had significantly higher levels of apolipoprotein C-III, a protein
that prevents the body from breaking down fatty molecules called triglycerides,
than the non-users. ApoC-III stops enzymes from chewing up triglycerides and
prevents the liver from processing the smaller fragments of the fat. This can
boost levels of triglycerides, which have been implicated in heart disease.
Other markers did not differ significantly between the groups.
Chronic cannabis use may elevate blood levels of apoC-III when the active ingredient in the drug, THC, binds to cannabinoid, or marijuana, receptors in the liver, says George Kunos of the National Institute of Alcohol Abuse and Alcoholism in Bethesda, Md., who was not involved in the study. “So once the receptors on the liver cells are activated by THC, they produce increasing amounts of apoC-III,” he says. Another possibility is that marijuana attaches to the cannabinoid receptors in the brain, causing a high, but also sending the liver instructions to boost production of apoC-III.
Isolated reports hinted at the link between marijuana and heart problems, Cadet says. But because marijuana is an illegal drug, it is difficult to study. And the researchers don’t yet know whether the effects are sustained once a person stops using the drug.
Teasing out the differences between frequent and occasional marijuana use may prove even trickier, Kunos says. Even if future studies show a link between heavy cannabis use and heart disease, it’s important not to over-generalize the results, he notes.
Cadet agrees: “The person who uses marijuana every so often might not be at risk.”
Scientists must look at larger groups to confirm the link between heart disease and heavy use, Kunos says. “Obviously, in this group of people who smoked a lot of marijuana, the level of this protein is increased, but we just speculate that it may lead to cardiovascular disease.” To be clinically meaningful, a study needs to track several hundred marijuana smokers over several years and compare their rates of disease with drug-free counterparts, he says.
The work also may have implications for people outside the stoner set, Kunos says. The body makes its own marijuana-like substances, which bind to cannabinoid receptors. Understanding the chemical pathway that links cannabis to heart disease may help scientists understand what happens when the natural pathway goes haywire, he says.