Now, a new study out of France has shown that young adults who smoke marijuana may be at risk for serious or even fatal heart problems.
The findings in the Journal of the American Heart Association raises new concerns about the safety of marijuana, just as many parts of the world are relaxing laws on its recreational use, and medicinal marijuana is gaining popularity for treating certain health conditions.
The risk of heart complications appeared small in the study, which included nearly 2,000 people who sought medical attention for complications related to smoking marijuana from 2006 to 2010.
Of those, two percent, or 35 people, had heart attacks or circulation problems related to arteries in the brain and limbs.
Of greater concern was the high death rate. One in four of the patients with cardiovascular complications died, said the researchers.
The analysis also found that the percentage of reported cardiovascular complications more than tripled from 2006 to 2010.
"The general public thinks marijuana is harmless, but information revealing the potential health dangers of marijuana use needs to be disseminated to the public, policymakers and healthcare providers," said lead author Emilie Jouanjus, a medical faculty member at the Centre Hospitalier Universitaire de Toulouse in Toulouse, France.
"There is now compelling evidence on the growing risk of marijuana-associated adverse cardiovascular effects, especially in young people," Jouanjus said.
Doctors should be aware of the heart risks and consider marijuana use as a potential contributor to cardiovascular disease in some patients, said Jouanjus.
People with pre-existing conditions appeared most vulnerable, the study added.
Valentin Fuster, director of Mount Sinai Heart and Physician-in-Chief of The Mount Sinai Hospital, said the study appeared to support some observations he has made at his own clinic in New York City.
"I am concerned about cannabis because we are running a clinic of young people who come to us with coronary artery disease. I have seen a number of cases in whom I was not able to identify any other risk other than the use of cannabis," said Fuster, who was not involved in the research.
"So I think this registry in France supports the issue that cannabis is not free of danger," he added.
"I am not sure if it is more risky than tobacco cigarette smoking or less, but one thing is clear, it's affecting young people."
Dr. Allen Taylor, professor of medicine at Georgetown University School of Medicine, said:
"This study shows a some preliminary evidence of cardiovascular harm from marijuana. It amounts to a signal of risk between marijuana smoking and heart troubles," he said.
Taylor added that more research needs to be done to assess the risks posed by marijuana.
"It is a shame that we simply don't know more about a substance that potentially carries the risk of serious bodily harm. It seems that public perception is ahead of the science. We should remain open to the scientific facts as they evolve."