Does THC Lower Heart Rate? Evidence, Mechanisms and Cardiovascular Effects of Cannabis
The long-term effects of cannabis on the heart are little understood.
THC (delta‑9‑tetrahydrocannabinol) is the main psychoactive compound in cannabis; its acute effects are well‑characterised (often increasing heart rate), but its longer-term impact on resting heart rate (RHR), blood pressure, vascular function and cardiovascular risk are less clear.
Does THC lower heart rate?
According to a study published in the American Journal of Medicine, cannabis consumers tend to have a lower RHR than those who don’t use the drug.
After analyzing the data of thousands of participants from a heart health study, researchers found that those who consumed cannabis had an average RHR of 65.9 beats per minute (bpm), while those who didn’t use the drug had a slightly faster average heart rate of 68.3 bpm.
Marijuana’s impact on heart rate
Cannabis use is known to increase a person’s heartbeat directly after consumption, but the drug’s long-term effects on the organ are less well understood.
To find out more, a research team from the University of Bern and the University of California, San Francisco looked at the data from the Coronary Artery Risk Development in Young Adults (CARDIA) study, an ongoing initiative that’s recorded the heart health of 5,115 participants across the US since 1985.
Out of the 3,269 participants that attended the 30-year CARDIA follow-up assessment, 2,785 (85 percent) claimed to have never used cannabis, while 471 (14 percent) said they were regularly consuming the drug.
After comparing the heart health data of these two groups, the research team found that the cannabis-sober participants had an average RHR of 68.4 bpm, while the cannabis-using participants had an average heart rate of 66.5 bpm.
Once the data had been adjusted for the participants’ demographics and health factors, the difference became starker; cannabis-sober participants had an average heart rate of 68.3 bpm, while cannabis-using participants had an average heart rate of 65.9 bpm.
There was no difference, however, between the heart rates of those who had no “cannabis years” (a measurement of how much cannabis the participants had collectively consumed in their lives) and those who had 10 cannabis years; after the data were adjusted, both groups had a heart rate of 68.2 bpm (Table 1).
“Current cannabis use was associated with lower resting heart rate, but cumulative cannabis exposure was not,” the researchers concluded.
As such, the researchers hypothesized that cannabis may have acute but transient effects on the heart that only temporarily lower its cardiac output.
Table 1. Resting heart rates in cannabis users vs non‑users.
| Study / Cohort | Population / Exposure | Unadjusted RHR Non‑Users (bpm) | Unadjusted RHR Users (bpm) | Adjusted RHR Non‑Users (bpm) | Adjusted RHR Users (bpm) |
| CARDIA (30‑yr follow‑up) | Regular cannabis users vs non‑users | ~68.4 | ~66.5 | ~68.3 | ~65.9 |
| Same CARDIA data for “no cannabis years” vs ~10 cannabis years | Cumulative exposure groups | — | — | ~68.2 | ~68.2 |
(Note: “—” denotes the study did not report separate unadjusted values for those cumulative exposure subgroups.)
How THC could alter heart rate over time
While THC acutely increases heart rate, several mechanisms have been proposed that could help explain a reduction in resting heart rate in regular users, or at least attenuate the acute increases. These include:
- Autonomic nervous system modulation
- CB1 receptor activation: THC binds CB1 receptors centrally and peripherally, influencing sympathetic and parasympathetic tone. Over repeated exposure, adaptive downregulation or desensitisation of some sympathetic responses may occur.
- Parasympathetic rebound: After acute activation of sympathetic activity, some regular users may experience relatively heightened parasympathetic tone at rest.
- Tolerance to cardiovascular effects
- With regular use, the acute cardiovascular effects (tachycardia, increased cardiac output, elevated blood pressure) may diminish in magnitude (pharmacologic tolerance), leading to lower resting heart rate over time in frequent users.
- Altered vascular function and hemodynamics
- Chronic cannabis use has been shown to impair endothelial function (via reduced nitric oxide availability, oxidative stress) and increase arterial stiffness (as measured by pulse wave velocity). These changes might change cardiac afterload and preload, influencing resting cardiac output and heart rate.
- Reduction in physical fitness, or lifestyle confounders
- Users may have different activity levels, sleep patterns or concomitant substance use; chronic physiological stress or altered baseline metabolic state may indirectly reduce resting metabolic demand, possibly lowering resting heart rate.
- Effect of mode of administration and cannabinoid profile
- THC‑predominant cannabis vs cannabidiol (CBD)‑predominant: Studies show that cardiovascular responses (heart rate, blood pressure, arterial stiffness) are more pronounced when THC is dominant. Mode (smoking vs vaporization vs edible) matters: inhaled THC causes rapid increase in heart rate, but repeated exposure via edibles is slower and may result in different adaptations.
Cannabis and the heart
The American Journal of Medicine study may have its limitations – there were no data on how the participants consumed their cannabis or how much they used, for instance – but the research team say their findings still add to the body of evidence “suggesting a lack of deleterious association of cannabis use at a level typical of the general population on surrogate outcomes of cardiovascular disease.”
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However, other studies have found that cannabis can have more concerning effects on heart health.
A paper published in the Canadian Medical Association Journal found that young adult cannabis consumers seem to be at a higher risk of having a heart attack than their cannabis-sober peers.
After assessing the survey data of thousands of young adults in the US, the research team found that 1.3 percent of self-identified cannabis consumers had a history of heart attacks, compared to around 0.8 percent of cannabis abstainers.
Research published in the Journal of Applied Physiology found that, compared to a control group, cannabis smokers had greater aortic stiffness, a factor linked to cardiovascular disease.
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Other long-term risks that have been associated with cannabis use include:
- Endothelial dysfunction: Regular cannabis smokers and users of THC edibles show significantly reduced vascular function (as measured by flow‑mediated dilation) compared to non‑users; similar in severity to that seen in tobacco smokers. Edible users have less serum evidence of systemic factors harming endothelial cells but still show functional impairment.
- Hypertension risk: Some observational studies have suggested a possible association between lifetime cannabis use and elevated blood pressure. More recent cohort work, however, has found no elevated risk of hypertension associated with cannabis use.
- Adverse cardiovascular events: A large pooled analysis of ~200 million people found ~29% higher risk of acute coronary syndrome, ~20% higher risk of stroke and roughly double the risk of dying from cardiovascular disease among cannabis users vs non‑users. However, the researchers acknowledge that there was a moderate to high risk of bias in most of the included studies, and most were observational, precluding the ability to draw causal inferences from the data.
Many researchers agree that further studies are still needed to properly assess the cardiovascular effects of cannabis.
“We do acknowledge the limited scope of evidence defining the cardiovascular safety of marijuana at present,” Dr. Muthiah Vaduganathan, a cardiologist at Brigham and Women's Hospital, Massachusetts, told Analytical Cannabis. “However, based on what we know, we believe there is sufficient evidence to give us pause.”
“We believe broader-scale clinical research is needed to better understand the safety of marijuana, especially on cardiovascular health,” he added.
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