Using cannabis, cocaine, or amphetamines may increase the risk of having a stroke, according to a major analysis led by researchers at the University of Cambridge.
The research brought together information from studies involving more than 100 million people, making it one of the largest investigations of recreational drug use and stroke risk.
Stroke is a medical emergency that happens when the blood supply to part of the brain is interrupted or when a blood vessel in the brain bursts. Without enough oxygen, brain cells can begin to die within minutes, which is why rapid treatment is so important.
There are two main types of stroke. An ischemic stroke occurs when a clot blocks blood flow to the brain, while a hemorrhagic stroke occurs when a blood vessel breaks and causes bleeding in or around the brain.
Stroke is a major cause of death and long-term disability around the world. Although age and family history can affect risk, many important risk factors can be changed, including smoking, high blood pressure, heavy alcohol use, poor diet, and low physical activity.
The Cambridge researchers wanted to understand whether recreational drugs should also be considered an important preventable risk factor. This question matters because the use of drugs such as cannabis, cocaine, and amphetamines is common in many countries.
Earlier studies had already suggested a connection between recreational drug use and stroke. However, many of those studies were relatively small or could not clearly separate the effects of the drugs from other differences between people who used them and those who did not.
For the new research, scientists from the University of Cambridge Department of Clinical Neurosciences combined results from many previous studies. This type of research is called a meta-analysis and can provide a broader picture by examining evidence from very large numbers of people.
The results were published in the International Journal of Stroke. Overall, the researchers found that cocaine, amphetamines, and cannabis were all associated with a higher risk of stroke.
Cocaine use was linked to a 96% higher risk, meaning the risk was close to twice as high. Amphetamine use was associated with a 122% increase, or more than double the risk.
Cannabis showed a smaller but still important association. People who used cannabis had about a 37% higher risk of stroke in the combined analysis.
The researchers did not find a statistically clear increase in stroke risk associated with opioid use. This does not mean opioids are safe, because they carry many other serious risks, including dependence and fatal overdose.
One of the most concerning findings involved younger adults. Stroke is more common in older people, but it can occur at any age, and the consequences can be especially severe for someone who experiences a stroke early in life.
Among people younger than 55, amphetamine use was linked to a 174% increase in stroke risk. That means the risk was nearly three times as high as in people who did not use amphetamines.
Cocaine use in this younger group was associated with a 97% higher risk. Cannabis was linked with a more modest increase of about 14%.
The researchers then used another method to investigate whether the drugs themselves might be contributing to stroke, rather than simply appearing alongside other risky behaviors. The method uses naturally occurring genetic differences that are associated with certain behaviors or health conditions.
This analysis provided evidence supporting a possible causal role for cocaine and cannabis use disorders. Cocaine use disorder was particularly associated with bleeding in the brain and with strokes caused by blood clots that form in the heart and then travel to the brain.
Cannabis use disorder was associated with stroke overall and showed a particular connection with strokes involving large arteries. The genetic evidence strengthens the argument that the relationship may not be explained entirely by other lifestyle factors.
The researchers also examined alcohol. Problematic alcohol use was associated with some types of stroke, while alcohol addiction was linked with a higher overall stroke risk.
There are several ways recreational drugs could affect the brain’s blood supply. Cocaine and amphetamines can cause sharp rises in blood pressure, placing sudden stress on blood vessels.
Some drugs can also cause blood vessels to tighten or go into spasm. If blood flow becomes severely restricted, part of the brain may not receive enough oxygen.
Recreational drugs may also disturb the heart’s normal rhythm. An abnormal rhythm can sometimes encourage blood clots to form in the heart, and a clot can then travel through the bloodstream until it blocks an artery in the brain.
Other possible effects include increased inflammation and changes in the body’s tendency to form blood clots. Amphetamines have also been linked with inflammation of blood vessels, which may further increase the chance of damage.
The study is important because it combines evidence from an exceptionally large population and uses more than one research method. The agreement between the large observational analysis and parts of the genetic analysis makes the findings more convincing than evidence from a single study alone.
However, the results still need careful interpretation. A meta-analysis depends on the quality of the studies included, and people may differ in how much of a drug they use, how often they use it, whether they use several substances together, and whether the substance contains unexpected contaminants.
The genetic method also has limitations and cannot answer every question about occasional or recreational use. In particular, the strongest genetic evidence concerned drug use disorders, which may represent heavier or more problematic use than occasional exposure.
The researchers were also unable to carry out the same genetic analysis for amphetamines because sufficiently large genetic datasets were not available. Future research will be needed to examine dose, frequency, combinations of drugs, and how risk changes after someone stops using them.
Overall, the findings provide strong evidence that recreational drug use deserves more attention as a possible stroke risk factor. The particularly large associations for cocaine and amphetamines, including among adults under 55, are especially concerning because stroke at a younger age can lead to decades of disability.
The study does not show that every person who uses cannabis, cocaine, or amphetamines will have a stroke. It does suggest, however, that these substances may add meaningful risk and that avoiding them could be one part of reducing preventable strokes.
Source: University of Cambridge.
