Regular marijuana use may enlarge the heart's main blood-pumping chamber, limited study in United Kingdom suggests

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Regular use of marijuana could cause changes in the structure of the heart, suggests a study conducted in Britain and reported in a journal of the American College of Cardiology.

"People who regularly use marijuana tend to have a larger left ventricle, which is the main pumping chamber of the heart, according to the findings," reports Dennis Thompson of HealthDay. "Routine stoners also appeared to have early signs of impaired heart function, measured by how the fibers of the heart muscle deform during contraction."

However, when marijuana use stops, "The heart appears to recover in both size and function," Thompson reports. "The researchers warn that the study 'should be interpreted with caution, and more research is required' to understand the potential mechanisms and dose-related effects of cannabis use."

That being said, "The results jibe with concerns people have had about the effects of pot on the heart, said Dr. Martha Gulati, editor-in-chief of the cardiology college's patient-education website.

"There's so much we don't know about cannabis use and its effect on the heart, but one of the things we do know is that when people use marijuana, particularly if they smoke it, the heart rate and the blood pressure go up, and the heart has to work harder," she said.

The study was published in one of the college's peer-reviewed journals, JACC Cardiovascular Imaging. (A review in the same journal said marijuana can interact with common heart medications, including statins and blood thinners, potentially putting patients at risk, NBC News reports.)

The study was observational, not controlled, so other factors may have caused the heart-structure changes, said Dr. Mary Ann McLaughlin, a cardiologist at Mount Sinai Hospital in New York City, who reviewed the findings for HealthDay.

"Alcohol can also cause similar types of changes in the left ventricle with chronic drinking, which can get better when people stop drinking," McLaughlin said. "They said they adjusted for alcohol use in this study, but the question is whether the use was adequately assessed."

Thompson notes, "Europeans also are known to mix their marijuana with tobacco, which has notoriously harmful effects on the heart," citing Paul Armentano, deputy director of the National Organization for the Reform of Marijuana Laws. "Experts also noted that the number of pot users in this study was very small." It observed 47 current, regular users and 105 previously regular users. The rest of the 3,400 sample from the United Kingdom "rarely used pot, if at all."

While more research is needed, Thompson writes, "Until there are more answers, people with heart problems might want to avoid pot, the experts said."

Gulati said, "If you have heart disease, you should really use marijuana with caution. In fact, I, as a cardiologist, would recommend you not to use it because of the physiologic effects of increasing your heart rate and putting more demand and stress on the heart."