"These findings provide compelling evidence that drugs like cocaine, amphetamines, and cannabis are causal risk factors for stroke," Ritson noted.

A stroke occurs when blood flow to part of the brain is interrupted. This can happen when a blood vessel becomes blocked by a clot, known as an ischemic stroke, or when a blood vessel bursts and causes bleeding in the brain, known as a hemorrhagic stroke. Both types can lead to serious brain damage and can be life threatening.

Amphetamines Associated With The Highest Risk

Among the substances examined, amphetamines were linked to the largest increase in stroke risk. Amphetamines are powerful stimulants that affect the central nervous system and can significantly increase heart rate and blood pressure. In illegal forms, they are often sold under street names such as meth or ice.

When researchers combined data from eight previous studies, they found that recreational amphetamine use was associated with more than double the risk of stroke across all adult age groups. For individuals under the age of 55, the increase was even greater. In this group, amphetamine use was linked to nearly triple the risk of stroke compared with people who do not use the drug.

Across all age groups, the analysis found that amphetamine use increased the risk of ischemic stroke by 137 percent and hemorrhagic stroke by 183 percent. These figures reflect relative risk, meaning the probability of stroke is higher among users compared with non users.

Cocaine Shows A Similar Pattern

The researchers also found a strong association between cocaine use and stroke. Cocaine is another central nervous system stimulant that can raise blood pressure and constrict blood vessels. These effects may increase strain on the brain's blood vessels and raise the likelihood of both clot formation and vessel rupture.

The analysis showed that cocaine use nearly doubled the risk of stroke of any kind and more than doubled the risk of hemorrhagic stroke. Additional genetic investigations were conducted alongside the main analysis to better understand whether the relationship might be causal rather than simply linked to other lifestyle factors.

Eric Harshfield, a genetic epidemiologist at the University of Cambridge, said the findings suggest the drugs themselves may play a direct role. "Our analysis suggests that it is these drugs themselves that increase the risk of stroke, not just other lifestyle factors among users," Harshfield said.

Cannabis Linked To Smaller But Significant Risk

Compared with amphetamines and cocaine, the association between cannabis use and stroke was smaller but still statistically significant. Researchers reviewed 19 previous studies investigating cannabis use and stroke outcomes. The analysis found that recreational cannabis use was associated with a 16 percent increase in the risk of any stroke and a 39 percent increase in the risk of ischemic stroke.

Among people under the age of 55, cannabis use was linked to a 14 percent increase in stroke risk. Although the increase is lower than that associated with stimulant drugs, researchers say it remains important because cannabis is widely used.

Opioids Showed No Clear Association

The analysis did not find evidence linking opioid use to an increased risk of stroke. However, researchers caution that stroke risk can be influenced by many factors. These include how long a person has used a drug, how much they use, their overall health, diet, genetics, and socioeconomic environment. Heavy alcohol use is also known to increase the risk of stroke and may worsen the effects of other substances.

A Preventable Health Risk

Experts say the findings highlight the need for greater awareness about how recreational drugs can affect long term health, particularly among younger people who may not associate stroke with their age group. "Illicit drug use is a preventable stroke risk," Ritson explained. "I don't know if young people are aware how high the risk is."

The researchers also note that many of the studies included in the analysis relied on participants reporting their own drug use. Because of this, other lifestyle factors could potentially influence the results. Further research will be needed to better understand the biological mechanisms involved and how different patterns of drug use may affect stroke risk. Still, scientists say the evidence now available provides an important foundation for future public health strategies.

"These findings give us stronger evidence to guide future research and public health strategies," Ritson said.

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