If your doctor prescribes Coumadin, don’t stop taking it without getting medical clearance.

That’s the strong recommendation of researchers who found that when people with a common heartbeat irregularity stop taking their blood thinner their risk of stroke soars.

Atrial fibrillation, a form of irregular heartbeat, raises the risk of stroke by 50 percent. To reduce the danger, doctors commonly prescribe a blood thinning drug called Coumadin (warfarin).

But if patients stop taking the medication, they face an 89 percent increased risk of stroke during the six months that follow, and a stroke risk of more than double for the six months after that.

Researchers from the University of Sydney also found people who skipped their Coumadin had a doubled stroke risk up to three years after they had discontinued taking the drug.

They reached their conclusions after scrutinizing a database of 68,288 patients with atrial fibrillation. The average age of the patients was 78 and slightly more than half were women.

The researchers also said they were concerned because more patients are being switched from Coumadin to blood thinners that require less monitoring. However, these newer blood thinners are shorter acting, so missing a pill could contribute to a higher stroke risk, they said.

The study was presented at the European Society of Cardiology in London.