Clinical observations in the early 1950s suggested that aspirin could prevent thromboses.

That translates to a *lot* of fliers -- 8 million people fly per *day,* for more than 1300 deep vein thromboses or pulmonary embolisms.

But some—especially those on anti-clotting drugs like warfarin, which are prescribed to prevent heart attacks, strokes and pulmonary thromboses—are at particular risk.