Cannabis users are often denied liver transplants. Scientists looked into whether that had any merit

Dr. Thomas Starzl, the "Father of Transplantation," performed the first successful liver transplant in 1967 while at the University of Colorado. Since then, thousands of similar operations are performed every year, with a record-breaking 9,200 liver transplants executed in 2021.

But people who use cannabis are often excluded from receiving liver transplants. That might seem odd, given how many people use in the United States; indeed, the Centers for Disease Control and Prevention estimates that 18 percent of Americans, or 48.2 million people, used cannabis in 2019.

There is generally no consensus from medical experts on cannabis use and organ transplants, but at least eight states have passed laws making it illegal to deny a transplant solely based on cannabis use. Still, cannabis users are regularly denied transplants elsewhere, with excuses ranging from its legal status to fears that the drug can increase fungal infections or cause the body to reject the new organ.

Yet the research on liver transplants and survival rates for cannabis users is frustratingly scant. To help get to the bottom of whether these kinds of transplant restrictions have any medical merit, researchers at the University of Alabama at Birmingham compared survival rates for liver transplantees based on their cannabis use. The study enrolled 111 patients who tested positive for cannabis using a urine drug screen during liver transplant evaluations between 2016 and 2021. The patients, who were 75 percent male, had many different types of liver disease requiring transplant, including from excessive alcohol use, viruses like hepatitis C, and fatty liver disease. As controls, the study included an additional 100 non-marijuana users who had all received liver transplants.

The researchers, writing in The American Journal of the Medical Sciences, noted that only 32 cannabis-using patients out of the 111 received a liver transplant. The remaining 79 were denied for varying reasons, including insurance or financial issues, with 41 explicitly denied for "continued marijuana use" as one of several non-compliance problems. Only 11 were denied solely for using cannabis.

The patients' medical records were examined for any complications, including heart, lung and kidney problems, as well as death. They were especially concerned with fungal infections. Invasive fungal infections are some of the most severe complications with liver transplants, especially a fungus called Aspergillus, which can also grow on cannabis plants. The fear is that by ingesting a cannabis product contaminated by Aspergillus, it would complicate the transplant, resulting in failure or death.

But the authors reported "there was no significant difference in overall mortality between marijuana users and non-users" and using marijuana prior to transplant "was not associated with post-transplant infections or readmissions up to one year post-surgery."

This study used a small sample size, and it only included patients from one location, at the University of Alabama at Birmingham, but previous research has uncovered similar results. A 2021 study in the journal Clinical Transplantation examined waitlist outcomes for 630 cannabis-using patients at University of Michigan and 2060 who reported no cannabis use. Those using cannabis were 33 percent less likely to be listed and experienced longer wait times, which the authors attribute to potential stigma.

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Of the 132 cannabis-using patients who were listed, 83 received a transplant, compared to 306 patients in the control group. Patient survival and rates of graft, which is the body accepting the transplant, were similar in both groups, the authors concluded.

Even prior to this study, some research has suggested that using cannabis may actually be helpful for transplants. Cannabidiol, or CBD, one of the main drugs in marijuana, has shown some protective benefits for the liver, but much of this research is in rats or mice, less so in humans.

With nearly 40 states that have legalized medical marijuana, with adult use legal in 19 states, plus D.C., and a handful of U.S. colonies, it's important to determine if cannabis really makes liver transplants more problematic. An estimated 2,500 people die every year waiting for liver transplants, with women around 10 percent more likely than men to die waiting. And some patients never even make it to the waiting list.

Yet another study in 2021, also in the journal Clinical Transplantation, found "no evidence" to suggest that using marijuana increased liver transplant complications or death. The authors concluded that "policies denying individuals with any marijuana use prior to [liver transplants] may be overly restrictive."

In all of these studies, the research was retrospective, which limits the conclusions that can be drawn. A randomized, clinical trial would be a better study design, but can be much more expensive and difficult to implement. Furthermore, it wasn't always possible to determine the frequency of marijuana use or the type of cannabis consumed.

Regardless, there still isn't much evidence that using cannabis will negatively impact an organ transplant, especially compared to something like alcohol use.

Stigma against cannabis users comes in many forms, including issues with memory loss or the myth that using marijuana makes you lazy. While not exactly harmless, these stereotypes don't come with the same level of mortal risks that people needing organ transplants face. Given the lack of data that cannabis use can harm liver transplants, it appears time to stop denying patients medical care based on their marijuana use.