The number of heart complications attributed to marijuana use increased slightly in France between 2006 and 2010, according to a new study.
The number of heart attacks and other cardiovascular problems blamed on marijuana increased from five events in 2006 to 11 events in 2010.
"It is true that we don't have a lot of cases, but it is important to keep in mind that cannabis use may be harmful," said Emilie Jouanjus, the study's lead author from Universite Toulouse III - Paul Sabatier in Toulouse, France.
While using tobacco, not exercising and being overweight or obese are known risk factors for heart disease, Jouanjus and her colleagues write in the Journal of the American Heart Association that past studies have also pointed to pot use.
While the drug is legal in many U.S. states for medical purposes, it remains illegal to use recreationally in all states except Washington and Colorado.
There has also been concern over a possible link between pot use and schizophrenia. Researchers can't say pot causes mental illness, though.
For the new study, the researchers used information from centers around France that collect data on the impact of drugs on public health. The centers collect reports from doctors who are legally obligated to report serious medical events that are related to drug use.
From 2006 through 2010, there were about 10,000 reports of medical events related to drug use in France. Of those, about one-fifth were attributed to pot use.
Thirty-five were cardiovascular events related to pot use, nine of which ended with the person's death.
Jouanjus emphasized that the reports do not just mean the person was smoking pot at the time of the heart complication. It would also be reported if a drug was one of the only factors that could have caused the problem, for instance.
In 2006, 1.1 percent of medical events thought to be caused by pot were cardiovascular events. That increased to 3.6 percent in 2010.
Most of the heart-related events were heart attacks, and most of the cases were among men and younger people.
"The central message of this publication is that cannabis use is not harmless," Jouanjus said. "It can be harmful and can lead to serious complications among patients who are young."
She added that the results may be an under-representation of the actual number of heart events related to pot use, because doctors may not report some cases and patients may be reluctant to admit that they use pot.
The researchers can't say exactly why there was an increase in marijuana-linked heart problems.
Dr. Shereif Rezkalla, who co-wrote an editorial accompanying the new study, told Reuters Health that patients should be forthcoming about any substances they are using. Doctors shouldn't be afraid to ask their patients about drug use either, he said. Rezkalla is a cardiologist at the Marshfield Clinic in Marshfield, Wis.
"We all know that legalizing marijuana is a controversial subject," he said. "We know when it's used as medicinal marijuana there is no problem with that with anybody. It helps some people with some conditions. The concern is for recreational use."
He said the U.S. should adopt a similar system as France to collect information on medical events related to pot - especially since it is now legal for recreational use in two states.
"We are not against people having fun, but I'd like them to have fun and live," Rezkalla said.
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