A new study shows that starting blood thinners just days after a stroke is not only safe—it significantly lowers the chance of another stroke.
The findings could help change how doctors treat stroke patients worldwide.
The new study in The Lancet finds that starting blood thinners within four days of an ischemic stroke caused by atrial fibrillation can significantly lower the risk of a second stroke—without increasing the risk of brain bleeding.
The findings offer the most definitive evidence to date on a question that has long challenged clinicians: How soon is too soon to begin blood-thinning therapy after stroke?
The study, called CATALYST, analyzed data from more than 5,400 patients across four major randomized clinical trials. Steven Warach, professor of neurology at Dell Medical School at The University of Texas at Austin, served as the US principal investigator and coauthor of the study. He also led the US-based START trial, one of the four studies included in the meta-analysis, which was published earlier this year in JAMA Neurology.
“For decades, clinicians have been uncertain when to safely start anticoagulation after stroke,” says Warach.
“This study provides the clearest evidence yet that in most cases, it’s not only safe to start earlier—it’s better for patients.”
Atrial fibrillation, an irregular heartbeat that increases stroke risk, causes about 1 in 3 ischemic strokes. Although direct oral anticoagulants (DOACs) are highly effective in preventing future strokes, the best time to start them after an initial stroke has remained controversial, with many physicians waiting one to two weeks to begin treatment.
By pooling individual patient data from all high-quality trials available, the CATALYST analysis offers a more reliable answer.
Key findings
- Starting DOACs within four days of stroke onset cut the risk of a second stroke by nearly one-third.
- No added risk of brain bleeding or other major complications.
- Benefits observed across a broad range of patients, regardless of stroke severity or prior treatment.
- Suggests earlier DOAC use should become the new standard of care.
- Potential to shorten hospital stays and improve global outcomes.
“This gives clinicians the clarity they’ve been waiting for—and gives patients a better chance at recovery,” says Warach. “It’s a major step forward in evidence-based stroke care.”
Source: University of Texas at Austin
