As more states legalize marijuana for both medicinal and recreational use and use increases nationwide, cardiologists should advise patients about the potential risks, including effects of marijuana with some commonly prescribed cardiovascular medications, according to a research review published today in the Journal of the American College of Cardiology.
The authors estimate that more than 2 million cardiovascular disease patients are currently using marijuana or have used marijuana previously. This includes recreational use and approved medical uses, such as human immunodeficiency virus-related weight loss, treatment of seizure disorders, or chemotherapy-associated nausea and vomiting.
"Some observational studies have suggested an association between marijuana and a range of cardiovascular risks," said lead author Muthiah Vaduganathan, MD, MPH, of Brigham and Women's Hospital's Heart and Vascular Center in Boston. "We also know that marijuana is becoming increasingly potent. Our review suggests that smoking marijuana carries many of the same cardiovascular health hazards as smoking tobacco. 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."
Certain cardiovascular medications, including statins and blood thinners, can be affected by marijuana use, the review found. For example, statin levels can increase in the blood when used together with marijuana because both are metabolized through a network of liver enzymes called the cytochrome P450 system. Levels of blood thinners such as warfarin also can be expected to increase when used together with marijuana.
"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."
The reviewers recommend that cardiologists screen their patients for marijuana use, asking them how often and how much they use. They also should ask about how they use marijuana.
"Vaping marijuana is becoming more and more common, and we know vaping marijuana increases the pharmacological effects of the drug," Vaduganathan said.
For patients who wish to continue to use marijuana, or who have other medically indicated reasons for use, the reviewers recommend limiting use as much as possible and for clinicians to inform patients that vaping and certain synthetic forms of cannabinoids are particularly potent and may have greater adverse effects.
In some patients, cardiologists should test for marijuana use by urine toxicology screening, the reviewers recommend. These include patients being considered for heart transplantation or those who present with early-onset heart attacks or heart failure at a young age.
The review also analyzed the current state of evidence linking marijuana use with cardiovascular health and disease.
Data on the exact health effects of marijuana on the cardiovascular system are limited, largely because federal laws that classify marijuana as a Schedule I drug have limited the ability of scientists to conduct high-quality research, Vaduganathan said.
"Now that we have seen marijuana use become more popular than tobacco smoking, we need more rigorous research, including randomized clinical trials, to explore the effects of marijuana on cardiovascular health," he said.
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