Pot may not have a chilling-out, calming effect on everyone — evidence is emerging that for some people, smoking marijuana could increase the risk of heart problems, doctors say.

In a new study, researchers used data from a database called the French Addictovigilance Network, gathered from 2006 to 2010. Of the nearly 2,000 reported complications related to marijuana, the researchers found that 2 percent, or 35 cases, involved heart problems. These cases included 20 people who suffered a heart attack, and nine who died.

Researchers found most patients were men, with an average age of about 34. Regular marijuana users with a family history of heart disease had an increased risk of heart disease, according to the study, published April 23 in the Journal of the American Heart Association.

Many of the patients also had other risk factors for heart disease, such as smoking tobacco and drinking alcohol, the researchers noted. Nevertheless, nearly half of the patients were regular users of only marijuana.

Researchers also found a small increase in heart problems over time. In 2006, only 1.1 percent of the reported complications were heart related, but that rate increased to 3.6 percent in 2010. [Marijuana: 5 Surprising Facts About Pot]

"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 health care providers," said study researcher Émilie Jouanjus, a medical faculty member at the Centre Hospitalier Universitaire de Toulouse in France.

Considering 1.2 million people in France use marijuana regularly, the number of reported complications may seem small. The researchers said, however, that the surveillance system may miss many drug-related complications.

This type of study cannot demonstrate a cause-and-effect relationship between marijuana and heart problems, but the findings underscore the need for more research on this topic, experts said.

"The study is very small and has many limitations, but it is a warning sign," said Dr. Suzanne Steinbaum, a cardiologist and the director of Women's Heart Health of Lenox Hill Hospital in New York.

"The perception is that marijuana is a magical drug, that it's totally safe, and we can use it in medical treatment. What we don't know about are the negative effects, the potential harms," said Steinbaum, who is also an op-ed contributor to LiveScience.

Several previous reports have linked marijuana use with serious heart problems. In one study involving nearly 4,000 patients, researchers found that people's risk of heart attacks increased five times in the first hour after marijuana use. This five-fold increase in risk is a little higher than the risk for sex, about the same as that for intense exercise, and much less than the risk caused by cocaine, which increases one's chance of having a heart attack 25-fold, the researchers told reporters last year.

Previous studies have also suggested marijuana use could increase heart rate and blood pressure, and reduce the blood's ability to carry oxygen, which may contribute to the higher risk for heart attacks.

Altogether, the new findings and evidence from previous studies suggest that, like any other drug, marijuana has its own share of risks.

"There is clear clinical evidence to suggest a therapeutic benefit of inhaled marijuana for the management of a number of chronic, debilitating conditions. However, clinical evidence also suggests the potential for serious cardiovascular risks associated with marijuana use, including myocardial infarction, serious cardiac arrhythmias, stroke and even death," Dr. Shereif Rezkalla, a cardiologist at the Marshfield Clinic, in Marshfield, Wisconsin, wrote in an editorial accompanying the new study.

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This story was originally written for LiveScience and has been republished with permission here. Copyright 2014 LiveScience, a TechMediaNetwork company.