antiplatelet drugs

Antiplatelet drugs interact with platelets, which is a type of blood cell, to block platelets from aggregating into harmful clots.

Ibuprofen does have an antiplatelet effect, but it's relatively mild and short-lived compared to aspirin or other commonly used antiplatelet drugs.

Anticoagulant drugs such as Heparin, Warfarin, Rixaroxaban, Dabigatran, etc.

If they have a history of having blood clots is a main reason. Possibly stroke, but I'm not positive. It just reduces the clotting factors in your blood.