By Alfred Bove, MD, PhD

There is much being said regarding the legalization of marijuana. The cover story in this month's CardioSource WorldNews reviews the issue and what cardiologists need to know. You may think it does not affect you, but the outright legalization of marijuana in a pair of states has to be seen in the context of its decriminalization in many more states, most of which have approved marijuana for medicinal use. Overall, more than half of the country's population resides in states where the drug is more widely available. (Just under half the states of the nation still maintain a total prohibition on cannabis.)

There are several disorders where cannabis appears to provide significant benefit when more conventional therapy has not been successful, but few randomized clinical trials have been done to identify disorders where the drug might be best used and most accounts of success have been anecdotal. Nevertheless, qualified practitioners who have demonstrated some knowledge of its therapeutic use have approved cannabis for medical use.

An important ethical dilemma arises for organ allocation committees who make decisions regarding eligibility for transplantation. Most such committees first identify patients who are eligible for a heart, liver, or kidney transplant due to medical need. Their ability to finance the transplant is reviewed, and the hospital finance staff seek insurance pathways to support the cost. The candidate's social situation, family support, and living conditions are reviewed, and a careful history is explored to identify smoking habits and drug abuse.

To date, medical marijuana use is infrequent among transplant candidates, and if properly indicated and prescribed, would not prohibit consideration of the patient for an organ transplant. However, illegal use of drugs for recreational purposes raises many concerns because of addiction issues, risk for endocarditis, and risk for arrest and incarceration. With the legalization of marijuana, concerns for the legal aspects of its use disappear, and concerns for medical complications like endocarditis from parenteral administration are not a concern.

The use of recreational drugs in the past has carried a stigma of illegality, addiction, adherence, and other behavior concerns that are not likely to rise in a legal, tempered marijuana user. Nevertheless, this will raise issues in transplant committees. A patient medically eligible for a heart transplant could argue that marijuana use should not be considered in the decision for approval, but even with greater societal acceptance, issues relating to the smoking of marijuana could arise—similar to issues with tobacco use.

We don't approve a heart transplant if the candidate is actively smoking. The reasons are two-fold. First, smoking increases risk for coronary disease, and the coronary arteries of a transplanted heart are already at increased risk of endothelial damage and acceleration of atherosclerosis due to immune injury. Smoking accelerates the process.

The second concern is related to lung cancer. The immunosuppressive medications required by all transplant recipients will increase risk for most cancers, and lung cancer risk is increased in smokers on drugs that suppress the immune system.

To date, decisions regarding recreational drug use in transplant candidates have not been a problem. Protocols define how to decide. Rejecting a candidate who legally uses marijuana is difficult without evidence of a detrimental effect on the heart or circulation. However, for reasons outlined in this month's cover story, it has been difficult to conduct research on the health effects of cannabis. We do have a case report from Spain suggesting that cannabis use may be detrimental in heart transplant patients.¹ We're conducting a huge experiment in the United States on the medical effects of marijuana, but I doubt if most users understand the implications of their participation.

More data are needed on long-term effects of marijuana on the heart and arteries, but at present, there seems to be no reason to reject a transplant candidate on the basis of legal marijuana use alone.

Alfred A. Bove, MD, PhD, is professor emeritus of medicine at Temple University School of Medicine in Philadelphia, and former president of the ACC.

Keywords: Kidney Transplantation, Atherosclerosis, Social Conditions, Smoking, Heart Transplantation, Immune System, Medical Marijuana, Endocarditis, Illicit Drugs, Liver Transplantation, Behavior, Addictive, Marijuana Smoking, Spain, Coronary Vessels, Tobacco Use Disorder, Cannabis, Lung Neoplasms

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