Recreational drugs significantly increase the risk of stroke

The recreational drugs cannabis, cocaine and amphetamines significantly increase the risk of stroke – including among younger users – Cambridge researchers have concluded after analyzing data from more than 100 million people.

Stroke is a major global health challenge – the third leading cause of death and disability combined. But it also a condition that, for the most part, results from modifiable risk factors, such as poor diet, lack of exercise and other lifestyle factors.

In 2024, 8.8% of adults aged 16 to 59 years in England and Wales – around 2.9 million individuals - reported having used a legal or illegal recreational drug in the past year. Recent data from the USA reports that over half of all those aged over 12 have used drugs such as cocaine, cannabis and opiates at least once.

There is increasing evidence that these drugs may increase the risk of stroke, but the evidence is often of differing quality and is observational only, meaning it is impossible to say whether the use of these drugs itself increases the risk of stroke, or whether this is purely a correlation.

To investigate this further, a team from the Department of Clinical Neurosciences at the University of Cambridge first carried out a meta-analysis of studies encompassing more than 100 million people. A meta-analysis is a method for pooling and analysing cohort data from all of the published evidence. This approach allows researchers to bring together studies which, on their own may not provide sufficient evidence and sometimes disagree with each other, to provide more robust conclusions.

In findings published today in the International Journal of Stroke, the team found that the use of cocaine and amphetamines was associated with around double the risk of stroke (cocaine increased the risk by 96%, amphetamines by 122%), while cannabis use increased the risk by around 37%. The team found no statistically significant link between opioid use and stroke risk.

When the researchers restricted their analysis to individuals under 55 years, they found that amphetamine use almost tripled the risk of stroke (an increase of 174%); cannabis use increase stroke risk but by a smaller amount (14%), while cocaine use increased the risk by 97%.

To analyse these links further, the researchers used a statistical technique known as Mendelian randomisation, which looks at naturally occurring genetic variants related to risk factors and stroke and uses these to evaluate whether there is evidence to support a causal association with a particular risk factor.

This analysis showed that cocaine use disorders were particularly associated with brain haemorrhage and cardioembolic stroke (where a blood clot forms in the heart and travels to the brain, blocking blood flow and leading to damage of brain tissue). Cannabis use disorders were associated with stroke overall, particularly large artery stroke. This genetic evidence suggests a causal link, rather than just correlation.

Problematic alcohol use was linked to an increased risk of cardioembolic stroke and large artery stroke, while alcohol addiction increased the risk of stroke overall.

The researchers were unable to use Mendelian randomisation to look at associations with amphetamine as there are currently no large genetic datasets available with information on their usage.

The researchers suggest that possible reasons why these drugs are linked to an increased risk of stroke include sudden spikes in blood pressure, blood vessel spasm and constriction, heart rhythm problems, increased blood clotting (especially cannabis), and inflammation or vasculitis (especially amphetamines). These are all well-established pathways known to cause both ischaemic strokes, which result from blood clots, and hemorrhagic strokes.

Dr Megan Ritson from the Stroke Research Group at the University of Cambridge said: "This is the most comprehensive analysis ever conducted on recreational drug use and stroke risk and provides compelling evidence that drugs like cocaine, amphetamines, and cannabis are causal risk factors for stroke. These findings give us stronger evidence to guide future research and public health strategies."

Our analysis suggests that it is these drugs themselves that increase the risk of stroke, not just other lifestyle factors among users. Taken together, our findings emphasise the importance of public health measures to reduce substance abuse as a way of helping also reduce stroke risk."

Dr. Eric Harshfield, Alzheimer's Society Research Fellow, Department of Clinical Neurosciences

The research was funded by the British Heart Foundation, with additional support from the National Institute for Health and Care Research Cambridge Biomedical Research Centre.