Younger adults who suffered a stroke were often smokers or had abused drugs or alcohol, in a new study from Ohio and Kentucky.
Although strokes are often thought of as a condition of the elderly, researchers said long-term changes in the heart, arteries and blood as a result of drug abuse or heavy drinking may put users at higher-than-average risk earlier in life.
It's also possible that some drugs, particularly cocaine and methamphetamines, may trigger a stroke more immediately, according to Dr. S. Andrew Josephson, a neurologist from the University of California, San Francisco, who has studied drug use and stroke.
Because substance use is common in older adults as well, he said doctors should ask anyone who's had a stroke about drugs and alcohol.
But, "we know that even with vascular risk factors that are prevalent - smoking, high blood pressure… most people still don't have a stroke until they're older," Josephson, who was not involved in the new study.
"When a young person has a stroke, it is probably much more likely that the cause of their stroke is something other than traditional risk factors."
According to the Centers for Disease Control and Prevention, close to 800,000 people in the United States have a stroke every year, and strokes are the most common cause of serious long-term disability.
One study of 2007 data found that almost five per cent of people who had a stroke that year were between ages 18 and 44.
The current study included people from Greater Cincinnati and Northern Kentucky who'd had a stroke before they hit 55.
Dr. Brett Kissela from the University of Cincinnati and his colleagues reviewed medical charts for blood or urine test results or other records of substance abuse for close to 1,200 stroke patients.
In 2005, the most recent year covered, just over half of younger adults who suffered a stroke were smokers at the time, and one in five used illicit drugs, including marijuana and cocaine.
Thirteen per cent of people had used drugs or alcohol within 24 hours of their stroke, according to findings published in the American Heart Association journal Stroke.
"The rate of substance abuse, particularly illicit drug abuse, is almost certainly an underestimate because toxicology screens were not obtained on all patients," said Dr. Steven Kittner, a professor of neurology at the University of Maryland School of Medicine in Baltimore who also wasn't part of the research team.
"It's certainly underreported," he told Reuters Health.
The rate of smoking, drug use and alcohol abuse - defined as three or more drinks per day - seemed to increase among stroke patients between the mid-1990s and the mid-2000s.
But Kissela and his team said they can't be sure whether more people were actually using those substances or doctors were just getting better at testing for and recording drug abuse.
The study also can't prove that patients' drug or alcohol use directly contributed to their strokes. It's possible, for example, that people who abuse drugs also see their doctors less often or engage in other risky behaviours that increase their chance of stroke, Josephson explained.
He said the study emphasizes the importance of learning and quickly recognising the signs of a stroke - such as weakness on one side of the body and dizziness - even for young people. Some treatments can only be used during a short "window of opportunity" after the stroke.
"We see patients all the time who have symptoms that are classic for a stroke… and those symptoms are not recognised as being stroke symptoms because of the idea that, 'Well, that's something that happens only to older people,'" he said.