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The study couldn't prove cause-and-effect, but the researchers said they tried to account for other heart risk factors.
"Even when we corrected for known risk factors, we still found a higher rate of both stroke and heart failure in these patients," explained lead researcher Dr. Aditi Kalla, a cardiologist at Einstein Medical Center in Philadelphia.
"That leads us to believe that there is something else going on besides just obesity or diet-related cardiovascular side effects," Kalla said in a news release from the American College of Cardiology (ACC).
Her team is slated to present its findings March 18 at the ACC's annual meeting, in Washington, D.C.
In the study, Kalla's group looked at 20 million health records of patients aged 18 to 55 who were discharged from one of more than a thousand hospitals across the United States in 2009 and 2010.
Of those patients, 1.5 percent said they'd used marijuana.
Such use was associated with a much higher risk for stroke, heart failure, coronary artery disease and sudden cardiac death. Pot use was also tied to common heart disease risk factors such as obesity, high blood pressure, smoking and drinking, the researchers said.
After adjusting for those risk factors, the researchers concluded that marijuana use was independently associated with a 26 percent increased risk of stroke and a 10 percent increased risk of heart failure.
"More research will be needed to understand the [reasons] behind this effect," Kalla said.
Not everyone agreed the findings are cause for alarm, however.
Paul Armentaro is deputy director of NORML, a marijuana advocacy group. He called the increase in heart risk, "a relatively nominal one," and said the study "is inconsistent with the findings of several other longitudinal studies finding that those who consume cannabis, but not tobacco, suffer no greater likelihood of adverse events compared to those with no history of use."
NORML agrees that certain groups -- adolescents, pregnant or nursing mothers, people with a history of psychiatric illness, or those with a prior history of heart disease -- may want to avoid marijuana due to the potential effects on health.
But others may want to talk the issue over with their doctors. "As with any medication, patients should consult thoroughly with their physician before deciding whether the medical use of cannabis is safe and appropriate," Armentaro said.
Study author Kalla noted that medical or recreational marijuana use is now legal in more than half of U.S. states -- so a better understanding of its health effects is needed.
"Like all other drugs, whether they're prescribed or not prescribed, we want to know the effects and side effects of this drug," Kalla said. "It's important for physicians to know these effects so we can better educate patients, such as those who are inquiring about the safety of cannabis or even asking for a prescription for cannabis."
Two heart specialists agreed.
The new study "suggests that marijuana may not be as safe as proponents for its legalization claim," said Dr. Andrew Rogove, who directs stroke care at Southside Hospital in Bay Shore, N.Y. He believes that "further studies need to be performed to elucidate how marijuana use can increase risk for stroke and heart failure and if any particular way that it is used confers a higher risk."
Dr. Shazia Alam directs inpatient stroke services at Winthrop-University Hospital, in Mineola, N.Y. She believes there's a growing number of patients of all ages with a history of marijuana use.
"As more of our patients will be on marijuana in the near future given the legalization trend, this study reminds us how important it is to ask about marijuana use early on and inform them of any potential consequences," she said.
Because these findings are to be presented at a medical meeting, they should be considered preliminary until published in a peer-reviewed journal.
-- Robert Preidt
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