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Patients undergoing percutaneous coronary intervention (PCI) after recent marijuana smoking tended to have different complications than non-users, researchers found.

Marijuana users -- representing a modest 3.5% of PCI recipients in the Blue Cross Blue Shield of Michigan Cardiovascular Consortium (BMC2) PCI registry -- experienced in-hospital outcomes characterized by:

• Higher risk of bleeding versus non-users (5.2% vs 3.4%, adjusted OR 1.54, 95% CI 1.20-1.97)
• More cerebrovascular accidents (0.3% vs 0.1%, respectively, adjusted OR 11.01, 95% CI 1.32-91.67)
• Lower risk of acute kidney injury (2.2% vs 2.9%, respectively, adjusted OR 0.61, 95% CI 0.42-0.87)

However, marijuana users and non-users had similar risks of transfusion and death in a propensity-matched analysis, reported Devraj Sukul, MD, MSc, of the University of Michigan in Ann Arbor, and colleagues in .

Marijuana remains a according to the U.S. Drug Enforcement Administration; randomized studies on marijuana are therefore still illegal despite the substance's legalization in many states.

Last year, the American Heart Association called for the loosening of marijuana rules for the sake of research.

"There are conflicting data surrounding the exact mechanism behind marijuana's effect on clotting. Some studies suggest impaired platelet aggregation and others increased thrombogenesis with modulation of platelet function through the endocannabinoid system. Interestingly, despite increased population-level use of marijuana, our understanding of the in vivo effects of marijuana on platelet function and cardiovascular health remains limited," Sukul and colleagues wrote.

Furthermore, given the signal of renoprotection with marijuana use in the present study, future investigations should probe the potential mechanisms behind this relationship in the PCI population, they said.

"Because of significant barriers to marijuana-related research at this time, we encourage an open conversation between clinicians and patients regarding the limited scientific data available to help inform discussion about the potential risks and benefits of marijuana use," the authors concluded.

For now, clinicians may have some insight into periprocedural in-hospital outcomes associated with marijuana use, but there are still few reports on postdischarge outcomes, lamented Mamas A. Mamas, DPhil, of Keele University in England, and Pablo Lamelas, MD, of the Instituto Cardiovascular de Buenos Aires and McMaster University in Hamilton, Ontario, in an .

"Given that it is estimated that more than 2 million adults with cardiovascular disease in the United States have used marijuana, and cannabinoids affect the anticoagulation cascade, platelet function and reactivity, and the efficacy of many of the drugs used in PCI, it is surprising that the effects of marijuana use on PCI outcomes have not received more widespread attention," they wrote.

"Bleeding avoidance strategies such as the radial-first approach should be adopted, and antithrombotic regimes (both type and duration) should be personalized at the individual patient level taking into consideration their overall balance of ischemic and bleeding risk and whether patients are likely to adhere to therapies," the duo suggested.

Sukul and colleagues identified 113,477 patients from the BMC2 PCI registry, who received PCI at 48 non-federal hospitals in Michigan in 2013-2016.

Marijuana use -- abstracted from the patient's medical record at the time of PCI and defined as the use of marijuana in an inhaled form at any time within 1 month prior to index PCI -- increased from 2.4% in the first quarter of 2013 to 3.8% in the third quarter of 2016.

Propensity matching produced 3,803 pairs of marijuana users and non-users for comparison.

The marijuana user cohort was more than a decade younger at the time of PCI and consisted of more men, Black people, and tobacco users. They tended to have fewer comorbidities and traditional risk factors, but presented more often with ST-segment elevation MI compared with controls.

In a post-hoc analysis, the two groups shared similar rates of hemodynamically significant arrhythmias and stent thrombosis.

Sukul's group acknowledged that their non-randomized study could not account for unmeasured confounders, such as structural racism, discrimination, and disparities in socioeconomic status and geography.

Another major limitation was the potential for reporting or ascertainment bias, they noted. "Patients may not have divulged their use of marijuana, given that our study period was prior to the legalization of marijuana for recreational use. Also, if a patient was not asked about his or her use, or it was not recorded in the medical record, the patient would be considered a non-user," they wrote.

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