Millions of people take anticoagulants (blood-thinners) on a regular basis. These prevent the formation of clots that can result in deep vein thrombosis (DVT) and pulmonary emboli (clots that break off and go into the lungs and can cause death).

Some people take them after a DVT episode to prevent a recurrence, and others take them because they have an inherited coagulopathy that is discovered in their blood. In some cases, people must be on life-time anticoagulants because they have an artificial heart valve that is known to increase the risks of clots forming and going to the brain.

The most common anticoagulant prescribed for these purposes is Coumadin (Warfarin), which almost always requires regular blood testing to be sure the INR level (a measure of blood thinning) is within the goal range.

There is also a class of drugs that are sometimes called blood-thinners, but actually act to breakdown clumps of platelets in the blood. Platelets are produced in the bone marrow. Aspirin is a drug that can act to block platelet formation. Another, which is often prescribed after cardiac stents are place, is Plavix.

The risk of anticoagulants is an increased tendency to bleed. A feared complication while taking these drugs is a fall that can cause a blow to the head and an intracranial bleed. But any trauma that can cause a bruise can also result in excessive bleeding, and sometimes internal bleeding can occur that isn’t diagnosed until it is fatal.

Any decision to prescribe anticoagulants must involve a weighing of the risks as well as the benefits. When I took Coumadin for six months after a DVT episode (apparently resulting from a long airplane ride), the doctor insisted on sitting down with me to discuss in detail the risks and benefits before discontinuing the anticoagulant.

A recent study in the JAMA Internal Medicine reported on studies showing that the use of aspirin and NSAIDS (Non-Steroidal Anti-Inflammatory Drugs) while taking anticoagulants can substantially increase the risks of bleeding. NSAIDs such as Aleve or Advil increased the risk in some patients by almost 2-fold, and aspirin had a 1.7-fold higher risk of clinically relevant bleeding. Common over-the-counter drugs may seem fairly innocuous, but care must be taken if one is also taking an anticoagulant.