But fast treatment remains patients' best hope of achieving recovery, researchers stressed.
The thrombolytic drug alteplase is currently licensed for use within three hours of an acute ischaemic stroke.
Researchers from the University of Heidelberg, Germany, looked at benefits for patients outside this window.
They randomised 821 patients presenting between three and 4.5 hours after onset of stroke to receive alteplase or placebo.
All endpoints studied showed benefits for a wide range of patients, but not all differences were statistically significant.
'Our results support the use of this thrombolytic drug in the extended period across a broad range of patient subgroups,' the researchers said.