Anti-coagulants such as aspirin or warfarin (Coumadin) thin the blood by keeping the platelets from clumping together to form a clot. These drugs usually have a short-acting effect.

For example, in the case of heparin used during surgery, this drug has a very short life. It is eliminated from the body in 30 or 40 minutes. The risk of bleeding is very minimal. The effects of other anti-inflammatory drugs last less than 24 hours.

A single dose of aspirin can suppress normal platelet clumping for 48 hours up to one week. It's not until new platelets form and are released that full clotting can occur again. That's why doctors tell patients to stop taking aspirin before any surgery. You wouldn’t bleed to death but you might bruise easily. The wound might ooze and fail to heal properly.