Thromboses - blood clots that form in the circulation - are easily the biggest single killer of British men and women. They affects people of all ages, races and ethnicities. Most strokes and heart attacks are caused by thromboses forming in the arteries supplying the heart or brain. But clots in the veins can be just as lethal, particularly when part of the clot breaks off and travels around the circulation and lodges in the lungs. Recently, the appearance of abnormal micro-clots in the lungs of severely affected Covid patients has highlighted the huge impact even tiny clots can have on our long term health and mortality. What more should be done to protect people from this misunderstood condition? James Gallagher unravels the risks and causes for blood clots, from deep vein thrombosis to clots in the lungs. As he hears from patients, the surprise of a DVT diagnosis and debilitation can be profound. Treating clots is a delicate process with a need to get the balance right between thinning the blood but preventing bleeding. James examines the effectiveness of the latest range of anticoagulants that have a more predictable blood thinning effect, without the need for regular checks to make sure the blood’s not too thick or too thin. The psychological effects of being diagnosed with thrombosis are often under reported. but in up to half the cases severe anxiety, depression and PTSD can arise. We hear of a major new study following the experiences of patients from their diagnosis to follow ups after treatment that explores how effectively they overcame the impact on their mental health of knowing they carried a blood clot. And James Gallagher reports on the newly emerging relationship between Covid and clotting. It was back in April when the alarm was first sounded about abnormal blood clots in severe Covid cases. Research is shedding new light on the causes of the problem - sticky blood. In turn, this knowledge is offering up new ways to treat some of the major complications thrown up by the virus. Presenter: James Gallagher Producer Adrian Washbourne