A review of research published this week is leading doctors to warn that the use of cannabis may interact with medications used to treat cardiovascular disease. The review was published online by the Journal of the American College of Cardiology on Monday.

Dr. Muthiah Vaduganathan, a cardiologist at the Brigham and Women’s Hospital in Boston and a lead author of the study, says that using marijuana can affect the efficacy of some medications used to treat cardiovascular disease, including statins and blood thinners. Because these drugs and cannabis are broken down in the liver by the same enzymes, marijuana use can increase the time they stay in the body, effectively increasing the dose.

For example, one study published last year found that using cannabis can interact with the effectiveness of the popular blood thinner warfarin. Patients who are using the drug may need to reduce the dose by as much as 30% to avoid excessive bleeding. Marijuana can also increase the potency of statins, potentially causing a dangerous drop in blood pressure. Vaduganathan advises patients to discuss their marijuana use with their doctors.

“The first step is having an open discussion with clinicians, because it does influence some parts of their care,” Vaduganathan said.

Once physicians are aware of their patients’ cannabis use, they can determine if their regimen of care should be modified.

“The review provides detailed tables of many drugs administered for various cardiovascular conditions, with the anticipated effects of marijuana on each one,” Vaduganathan said. “These will be helpful to cardiologists and pharmacists reviewing patients’ medications and will help them collaboratively decide whether they need to adjust dosing if the patient continues to use marijuana.”

Smoking Pot Not Risk-Free

The review of the available evidence, which the study’s authors admit is limited, also showed that some methods of cannabis consumption may be riskier than others.

“Our review suggests that smoking marijuana carries many of the same cardiovascular health hazards as smoking tobacco,” Vaduganathan said. “While the level of evidence is modest, there’s enough data for us to advise caution in using marijuana for our highest-risk patients, including those who present with a heart attack or new arrhythmia, or who have been hospitalized with heart failure.”

Dr. Sergio Fazio, a professor of cardiovascular medicine at Oregon Health and Science University in Portland who was not involved in the research, advises that edibles are safer than smoking or vaping cannabis. And he acknowledges that some cannabis use, particularly if it reduces stress, may actually contribute to cardiovascular health, although he advises against excessive use.

“Anytime someone says that they were able to get eight hours of peaceful sleep because they used a little bit of marijuana, their cardiovascular health will likely be better off with the use of marijuana,” Fazio said. “When you move to the purely recreational use, that’s where the risks associated with heart problems potentially outweigh the benefits.”