Over the last week, we’ve seen many headlines about 2 new studies that found “marijuana use raises risk of heart attack, heart failure and stroke.” In this article, I’ll review what we know and don’t know about the new findings (including some juicy details that didn’t make it to the media reports), compare with some of the previous publications on this topic, and boil it down to what matters for people with cardiovascular disease or cardiovascular risks who want to safely use cannabis. Let’s start by taking a look at the new data and what it means.
First, it’s important to point out that I usually wait until new data makes its way through the scientific peer-review process and is published in a journal before giving it much time and energy. Neither of these studies fit those criteria – they were preliminary reports presented at a recent American Heart Association conference. At this point, we don’t have access to anything more than the abstracts, which allow no opportunity for understanding the authors’ detailed consideration of the data, scrutinizing their methods, or understanding how this data relates to what’s already known about this topic.
Here’s what I do know about the first presentation:
- 156,999 people without heart failure were followed for a median 45 months.
- During that time, 2,958 (1.9%) developed heart failure.
- Researchers compared those who had never used cannabis with those who had, adjusting the data to account for differences in age, sex, race, ethnicity, alcohol and tobacco use, educational attainment, employment status, income, health insurance coverage, and the presence of diabetes, hypertension, hyperlipidemia, and body mass index.
- After making all of those adjustments, daily cannabis use (but not weekly or monthly) was associated with a 34% increase in heart failure, which was marginally statistically significant.
- After adding a diagnosis of coronary artery disease (CAD) to the list of conditions for which the data was controlled, there was no longer a statistically significant association between daily cannabis use and heart failure.
- This led the authors to suspect that the way in which daily cannabis use was increasing the risk of heart failure was by increasing the risk of CAD.
It’s also important to point out that while a 34% increase in heart failure sounds like a lot, when you consider the 1.9% incidence of heart failure in the entire group, that’s an absolute difference of around 0.6%. In other words, the daily cannabis users had an incidence of heart failure of approximately 2.5%.
The second presentation was even less compelling:
- It compared 28,535 people who have been labeled with “cannabis use disorder” (CUD) who don’t smoke tobacco with >10 million people who also don’t smoke tobacco and don’t have CUD. All of the subjects were admitted to the hospital and were over the age of 65.
- There were major differences between the two groups:
- Those with CUD were more likely to be male, black, have AIDS, alcohol abuse, depression, uncomplicated hypertension, and drug abuse.
- Those with CUD were less likely to have complicated hypertension, diabetes, hyperlipidemia, obesity, thyroid issues, previous strokes, blood clots, and cancer.
- Without controlling for any of the factors mentioned above, the researchers showed that those with CUD had 20% more major adverse cardiac and cerebrovascular events.
- Importantly, the authors failed to mention that among those with CUD, the rate of all-cause mortality was ~50% lower (1.7% vs. 3.3%)
I admit that there are compounds in cannabis smoke, like other types of smoke, that are harmful to the cardiovascular system. The presence of other risk factors, amount and frequency of smoking, and individual differences all modify just how much risk this poses.
Unfortunately, neither of these reports tells us anything about how these subjects were using cannabis, except the first one which stratified daily vs less than daily use. Were they smoking vape pens, joints, bongs, or were they using flower vaporizers and oral products? Were they heavy users that built tolerance? Were they using cannabis to treat another medical condition? Did these differences in behavior change the risk of an adverse outcome? We’ll likely never know.
What I do know is that both of these questions have been answered by other studies that have made it through peer-review and rely on more robust data sets. If you’d like to read a careful analysis of the large body of evidence on this topic that is overly critical of cannabis but still looks at nuances, a review article from the journal Circulation published in 2020 is a good place to start. This review includes evidence from the CARDIA study that followed subjects for >25 years and found no association between cumulative lifetime and recent cannabis use with cardiovascular disease, stroke, coronary heart disease, or cardiac mortality.
Cross-sectional data, like the second presentation described above, essentially compares a snapshot of the cannabis users vs non-users, and is less compelling than longitudinal data that follows people over time and compares their outcomes in the context of other factors, like the first presentation. Longitudinal data with a median of 45 months duration typically provides a lot less information that one that has followed subjects for decades.
It’s also important to point out that the second presentation described above was not the first to find that cannabis users hospitalized for cardiovascular events are less likely to die than non-users, though the difference was the biggest one yet; at least two other studies have shown 21% and 26% lower mortality rates in cannabis users who have a heart attack.
In the latter, the best the authors could say was, “the odds of mortality was not significantly increased” in the cannabis users. If you want to find the evidence of 26% lower mortality, you’ll have to read the fine print. It’s a good reminder that scientific bias against cannabis is still alive and well. Similar findings have been published showing lower rates of mortality in cannabis users who have traumatic brain injury and brain hemorrhage.
Finally, it’s important to point out that compounds in cannabis, including CBD and ultra-low-dose THC, have been shown in several animal studies to have a protective effect on the heart and brain in models of heart attack and stroke, which explains why cannabis users who suffer these outcomes may have better outcomes.
So, what’s the take-home message for those who want to use cannabis without increasing their cardiovascular risk?
- Use cannabis in a way that promotes restorative sleep, decreased anxiety and stress, improved mood, and increased beneficial social interactions. We have many free resources on Healer.com that will help you do this.
- Limit or avoid smoking cannabis and using vape pens. Instead, use a flower vaporizer, drops, capsules, gummies, tea, and topical products.
- Choose “clean” cannabis products that have been shown to be free from contaminants and accurately labeled based on third-party lab testing.
- Use the lowest effective dose of cannabis to relieve symptoms and avoid building tolerance. If you have built tolerance, reverse it using our Sensitization program.
- If you’re wary about using THC, there are many highly effective hemp-based products that can relieve symptoms with no risk of impairment.
- Work with a cannabis expert. If you have a medical condition that you’d like to treat with cannabis, find a local cannabis expert at the Society of Cannabis Clinicians.
- Pay less attention to news headlines (in general), especially those that exaggerate non-peer-reviewed findings about the harms of cannabis!
Cannabis is one of the most versatile, safe, and effective medicinal plants on the planet. With its immense power to heal, it certainly also has the power to harm, though the risk is much less than most of the drugs it can replace. We have a lot more to learn about the healing properties and risks of cannabis, but until then, I plan to continue treating my patients with cardiovascular disease or risk factors with cannabis when appropriate.