It’s news to take very seriously if you take the blood thinner Warfarin. A study out of McGill University suggests taking the drug to treat irregular heartbeat may lead to a temporary spike in the risk of stroke. Researchers say the drug may initially cause what they call a hyper-coagulable state in which the blood becomes stickier and more likely to clot. The study found the stroke risk was particularly high in the first week after patients started to take Warfarin, peaking at about three days. After 30 days, that risk dropped by half, compared to patients not taking the drug.