Medical Cannabis Authorization Linked to Modestly Higher Heart Failure Risk in Large Ontario Study
By Dr. Benjamin Caplan, MD | Board-Certified Family Physician, CMO at CED Clinic | Evidence Watch
A large Ontario study of over 215,000 people found that patients authorized to use medical cannabis had a modest 13 to 15 percent higher rate of heart failure-related emergency visits and hospitalizations compared to matched controls. However, because the study could not confirm whether patients actually used cannabis or account for the underlying health conditions that prompted them to seek it, this association should not be interpreted as proof that cannabis causes heart failure.
Medical Cannabis Authorization Linked to Modestly Higher Heart Failure Risk in Large Ontario Study
A retrospective cohort of over 215,000 Ontarians finds a 13 to 15 percent higher hazard of heart failure events in cannabis-authorized patients compared to general population controls, but the observational design, inability to verify actual cannabis consumption, and strong potential for confounding by indication all prevent any conclusion that cannabis itself caused the elevated risk.
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Strong Clinical Relevance
One of the largest medical cannabis cardiovascular cohorts to date, directly relevant to clinical counseling, though observational limitations constrain its actionability.
Heart Failure
Cardiovascular Safety
Observational Epidemiology
Confounding by Indication
Medical cannabis use is expanding rapidly across North America, yet its cardiovascular safety profile remains one of the most poorly characterized areas in cannabinoid medicine. Heart failure affects over six million Americans and is a leading driver of emergency utilization and hospitalization costs. Clinicians who authorize cannabis need population-scale data to guide counseling about cardiac risk, and most prior work has focused on recreational use or cannabis use disorder rather than the medically authorized population. This study provides some of the first large-cohort, real-world evidence specifically addressing that gap, making it directly relevant to how physicians discuss cardiovascular considerations with patients seeking cannabis for chronic pain, insomnia, or anxiety.
Heart failure is a condition characterized by progressive decline in cardiac function, and several mechanistic pathways have been proposed through which cannabinoids could influence cardiovascular risk, including effects on heart rate, blood pressure, and vascular tone mediated through CB1 receptor activation. This retrospective cohort study from Ontario linked electronic medical records from licensed cannabis clinics to provincial health administrative databases to examine whether adults authorized to use medical cannabis experienced higher rates of heart failure events. The study enrolled 54,006 cannabis-authorized patients and 161,265 age- and sex-matched general population controls, applying inverse probability of treatment weighting based on propensity scores to balance measured baseline characteristics between the two groups. The cohort was relatively young (39% aged 50 years or younger) and predominantly female (55%), reflecting the demographics of Ontario’s medical cannabis patient population during the 2014 to 2019 authorization period.
The primary outcome, a composite of emergency department visits and hospitalizations for heart failure, occurred at an incidence rate of 5.87 per 1,000 person-years among cannabis-authorized patients versus 5.14 per 1,000 person-years among controls, yielding a weighted hazard ratio of 1.15 (95% CI 1.06 to 1.25). When outpatient physician claims for heart failure were added to the composite, the hazard ratio was 1.13 (95% CI 1.08 to 1.19). The absolute rate difference for the primary outcome was approximately 0.73 per 1,000 person-years. Critically, exposure was defined by authorization alone, not confirmed consumption, dose, route of administration, or THC-to-CBD ratio. The authors acknowledge that confounding by indication, where the underlying conditions prompting cannabis use may independently elevate cardiovascular risk, represents a major limitation that propensity score weighting cannot fully resolve. They conclude that prospective studies with validated exposure measurement are needed before clinical recommendations can change.
This is a well-powered, methodologically respectable study and I appreciate that the investigators chose to study the authorized medical cannabis population rather than lumping it in with recreational users or people with cannabis use disorder. The 15% hazard ratio is genuinely informative as a signal. But here is the fundamental problem: the study cannot tell us whether patients actually consumed the cannabis they were authorized, what products they used, how much THC they were exposed to, or whether the conditions that drove them to seek cannabis, such as chronic pain, anxiety, or poor sleep, were themselves the real cardiovascular risk factors. A 0.73 per 1,000 person-year absolute difference sits comfortably within what residual confounding alone could explain.
In my practice, I already screen every patient for cardiovascular history before recommending cannabis, and I preferentially guide patients with cardiac risk factors toward lower-THC, higher-CBD formulations and non-inhaled routes of administration. This study does not change that approach, but it reinforces why the conversation about heart health belongs in every cannabis consultation. I tell patients that we do not have evidence that medical cannabis causes heart failure, but we also cannot guarantee it is neutral for the heart, and that honest framing is what the data actually supports.
This study sits at an early-to-middle position in the cardiovascular safety research arc for medical cannabis. It establishes a plausible signal from a large, real-world population, but it cannot move beyond signal generation because of its observational design and exposure measurement limitations. Prior cohort analyses and case-control studies have suggested associations between cannabis use and arrhythmias, myocardial infarction, and stroke, but most were conducted in recreational-use or substance-use-disorder populations with different risk profiles. Clinicians should interpret this study as hypothesis-generating rather than practice-changing. The effect size, while statistically significant, is modest enough that it could be entirely attributable to unmeasured confounders.
From a pharmacological standpoint, THC is known to acutely increase heart rate and can cause orthostatic hypotension, both of which could theoretically stress a failing or vulnerable heart. CBD, in contrast, has shown cardioprotective properties
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