Hackam's team combed the medical literature to find studies on SSRIs and brain hemorrhage.
The drugs are known to raise the risk of gastrointestinal bleeding. Studies on their link with brain bleeding have mixed findings, Hackam says.
To be included in the new analysis, studies had to include a comparison group that wasn't on SSRIs and meet other scientific criteria.
Hackam found that people taking SSRIs were about 40% or 50% more likely than those not on the drugs to have strokes known as intracranial hemorrhages or intracerebral hemorrhages.
These types of strokes are rare, Hackam says. Although a 50% increase sounds high, it does not translate to a high actual or "absolute" risk, he says.
About 25 of these types of strokes occur per 100,000 people per year, he says. Based on his findings, one more would occur for every 10,000 people on the drugs for a year, he estimates.
The risk of stroke found for those taking SSRIs who already had risk factors for strokes, such as being on anticoagulants or blood thinners, was higher, the researchers found.
Those on SSRIs who are already at risk for stroke should talk to their doctor, Hackam says. "If you are already taking blood thinners or antiplatelet drugs, you should talk to your doctor about which is the most appropriate class of antidepressants you should take."
SSRIs slow down the rate of blood clot formation. This is thought to explain the link between antidepressants and hemorrhagic stroke risk.
Antidepressants and Stroke Risk: Perspectives
With so many people on SSRIs, the new analysis is important, says Jordan Smoller, MD, ScD, associate professor of psychiatry at Harvard Medical School. He has also researched the link.
However, he points out some important caveats. All the studies are observational, he says. "So they can tell us there is a correlation, but that doesn't necessarily mean that there is a causal connection."
The individual risk for bleeding is still low, he says.
"And, we should remember that the conditions people take SSRIs for -- depression and anxiety -- have their own risks in terms of adverse health outcomes, suffering, disability, and even suicide," Smoller says. "So it's not a matter of risk versus no risk."
WebMD contacted SSRI manufacturers for comment on the study. MacKay Jimeson, a spokesperson for Pfizer, which makes Zoloft, declined to comment. Spokespeople for Eli Lilly, which makes Prozac, did not comment. Representatives from Forest Laboratories, which makes Celexa, Lexapro, and Viibryd, also declined comment.
Daniel Hackam, MD, PhD, associate professor of medicine, Western University, London, Ontario, Canada.
Jordan Smoller, MD, ScD, associate professor of psychiatry, Harvard Medical School; associate professor of epidemiology, Harvard School of Public Health, associate vice chair of psychiatry, Massachusetts General Hospital, Boston.