A panel of independent experts has decided that a clot-busting drug often used to treat strokes is "safe and effective".
The UK medicines watchdog wanted after concerns were raised about its safety.
The panel concluded that the best time to use the drug is up to four and a half hours after the start of symptoms.
But some other doctors are still not convinced by the evidence.
Most strokes are caused by a clot blocking the flow of blood to the brain.
Many patients are given the drug alteplase to break down and disperse the clot - a treatment known as thrombolysis.
Benefits outweigh risks
The independent expert panel, chaired by Prof Sir Ian Weller, said it had looked at all available data on alteplase and decided that the earlier the drug was given to patients, the greater the chance of a good outcome.
Used up to four and a half hours after the onset of symptoms, the benefits of the drug were found to outweigh the risks.
But it added that the benefits of using alteplase to treat strokes were "highly time-dependent" and, in a small number of people, there was a risk of haemorrhage.
Prof Weller explained: "The evidence shows that for every 100 patients treated with alteplase, whilst there is an early risk of a fatal bleed in two patients, after three to six months, around 10 more in every 100 are disability-free when treated within three hours."
Five more patients in every 100 are left with no disabilities when treated between three and four-and-a-half hours after a stroke, he said.
However, there are still medical experts who have concerns.