Are cannabis consumers really more at risk of a heart attack?

As new research links frequent cannabis use to an increased risk of heart problems, we look beyond the sensationalism and break down what you need to know. 

According to a recent media reports, cannabis users are ‘up to a third more likely to suffer a heart attack’, in what the Daily Mail describes as ‘another blow to the idea that marijuana is safe’.

So, as a regular cannabis consumer should you be concerned that you’re putting yourself at risk of heart problems further down the line? Certainly, no substance or medication comes without its risks, but it’s not quite as cut-and-dry as the Mail makes out. 

The article, which was published on 24 February, is referring to a new study from researchers at Stanford University, which has linked daily cannabis use with an increased risk of developing coronary artery disease (CAD).

CAD is the most common form of heart disease and occurs when the arteries that supply blood to the heart become narrowed due to a buildup of cholesterol. It causes chest pain, shortness of breath and fatigue, and in some cases can lead to a heart attack.

However, the article glossed over some of the key details which we explore below.

What the study actually found 

Using data from 175,000 people from the All of Us Research Program of the National Institutes of Health, researchers first analysed the relationship between cannabis use frequency (assessed using surveys at the time of enrolment in the study) and rates of CAD (assessed based on medical records spanning several years). 

After adjusting for age, sex and major cardiovascular risk factors, the results indicated that daily cannabis users were 34% more likely to have CAD than those who have never used cannabis. In contrast, monthly cannabis use was not associated with a significant increase in the risk of CAD. 

Further analysis suggested that this was due to a causal relationship, finding that people with cannabis use disorder were more likely to develop CAD.

Cannabis use disorder is a recognised psychiatric disorder defined as the recurrent use of cannabis despite adverse consequences, causing clinically significant impairments or distress. According to figures from the CDC, approximately three in 10 cannabis consumers become dependent, with CUD thought to affect around 13 million people globally.

In the genetic analysis, this causal relationship was independent of the potential confounding effects of tobacco and alcohol use.

Dr Ishan Paranjpe, a resident physician at Stanford University and the study’s lead author commented on the findings: “We found that cannabis use is linked to CAD, and there seems to be a dose-response relationship in that more frequent cannabis use is associated with a higher risk of CAD.

“In terms of the public health message, it shows that there are probably certain harms of cannabis use that weren’t recognised before, and people should take that into account.”

However, the research is limited in that the datasets used in the study did not differentiate between various forms of cannabis use—for example, whether the drug was smoked or consumed in edibles or other forms. 

Since THC enters the body through a different pathway and gets to the brain more quickly when cannabis is smoked rather than ingested, researchers said it could be helpful to examine the health implications of these different forms of cannabis consumption in future studies.

What previous research has shown

This is not the first study to link frequent cannabis use with higher risk of cardiovascular problems. 

Previous research, also from Stanford University has suggested that THC acts on receptors that are found in the central nervous system and in the heart and blood vessels. This interaction between THC and blood vessels may provide a pathway for cannabis to promote inflammation and the buildup of plaque, ultimately leading to CAD. 

However, this study was carried out using data on people whose chosen method of consumption was smoking and didn’t account for those who also used tobacco, which is widely known to be linked to cardiovascular problems.  

Meanwhile, other studies have suggested that THC may have a protective effect on the heart, but this also requires further investigation.

Results from an animal study showed that THC protected the heart, following ischemia-reperfusion injury, the damage caused when blood supply returns to tissue, following a period of lack of oxygen, which was evidenced by the improved recovery of cardiac function.

What you need to know about the risks 

Based on the new findings, Stanford University researchers have said it is important for people to be aware that cannabis use is not without risk. 

There is some evidence that frequent consumption of THC could increase the risk of heart and circulation problems, which is certainly something to be mindful of. 

Researchers have advised frequent consumers to make sure to inform their doctor if they use cannabis so that clinicians can take appropriate steps to monitor their heart health.

What if you are a medical consumer?

Commenting on the findings of the study, Professor Mike Barnes, a neurologist and chair of the Medical Cannabis Clinicians Society in the UK, advised that patients should be aware of its potential risks, as they would any other medication. 

“This is an interesting study. It has been known for many years that excessive use of high-THC cannabis might cause heart and circulation problems. Obviously, like any other medicine, it is not entirely safe and needs to be prescribed sensibly,” he commented.

However, Professor Barnes added that more research needs to be carried out in this area and that those prescribed cannabis under the guidance of a clinician should not have too much cause for concern.

He continued: “The work needs replicating and not just accepted at face value, but is of interest. It should be noted that in this study, apparently it is only those with frequent daily use with cannabis use disorder that have an increased risk. Cannabis use disorder is a recognised addiction problem that occurs in about 9% of persistent street users.”

Professor Barnes added: “It is important to note that if properly prescribed there is no evidence at all that medical users will have this issue.”

Professor Barnes has also previously said that he would avoid prescribing cannabis within three months of a heart attack or stroke or in ‘anyone who would not benefit from an increased heart rate which occurs with THC’.

The full study will be presented at the American College of Cardiology’s Annual Scientific Session Together With the World Congress of Cardiology.