It’s well-known that someone having a stroke needs to be taken to an emergency room within three hours.

That’s so doctors can administer a powerful brain-saving medicine. But after three hours, doctors won’t normally give the medication because they are afraid it will do more harm than good.

But Stanford University scientists think stroke sufferers have an entire hour-and-a-half longer to receive the the clot-breaking medicine.

Each year in the United States there are more than 780,000 strokes, according to the National Institute of Neurological Disorders and Stroke. Signs of a stroke include numbness or weakness of the face and limbs, sudden confusion, trouble speaking or loss of vision.

It causes more long-term disabilities than any other disease in the country and it is the third leading cause of death in the country.

Looking at data from six major clinical trials, Stanford researchers determined how much of a given medicine was needed to provide a health benefit or, conversely, to cause harm.

They studied the intravenously administered enzyme called tissue plasminogen [PLAZ-MINN-O-GEN], which works to break down blood clots, and assessed patient data in ninety-minute intervals from the onset of stroke symptoms.

But the therapeutic window in which the medicine showed a much greater potential to help than harm was four-and-a-half hours.

Whether that becomes a standard measure of time in emergency rooms across the country remains to be seen… more studies are needed.

But the true lesson remains… when it comes to stroke, the sooner patients are treated, the better their chances for recovery.