Drug Therapy: Anticoagulants

Anticoagulants do not actually make the blood thinner. These drugs prevent the blood from forming clots, which can block arteries, veins or the valves of the heart. Common anticoagulants are aspirin, warfarin and heparin.

Anticoagulants help reduce the risk for heart attack, stroke and blockages in veins and arteries, such as ones caused by phlebitis. While these types of drugs can prevent a clot from forming, they do not have an impact on a clot that already exists.

Blood-thinning drugs are given to people who have had a heart valve replaced or who have atrial fibrillation or congestive heart failure. These may be given to a person who is at risk of having a heart attack to prevent blood clots in the arteries of the heart or to people who are at risk of a clot forming in the heart's chambers.

Certain types of drugs (including some over-the-counter pain relievers, such as aspirin) can combine with anticoagulants to cause an even greater anti-clotting effect. If anticoagulants are prescribed, the doctor should be made aware of any other drug, vitamin, mineral or herbal supplement the patient is taking, especially:

  • Antacids
  • Antiarrhythmics
  • Antibiotics
  • Anticonvulsive drugs
  • Antidepressants
  • Antihistamines
  • Aspirin, acetaminophen (Tylenol®, Excedrin®), ibuprofen (Motrin®, Advil®) or naproxen (Aleve®)
  • Calcium or vitamin K supplements
  • Corticosteroids, such as prednisone or cortisone-like medications
  • Medicines for treating an overactive thyroid
  • Sleeping pills
  • Some antifungal medicines
Smoking and drinking alcohol can also make the effect of blood-thinning drugs more powerful. Be aware that vitamin K (which is found in fish, liver, spinach, cabbage, cauliflower and Brussels sprouts) can make blood-thinning drugs less effective. Patients who eat these foods must be careful not to eat too much.

Conditions that put the patient at risk of bleeding or bruising require particular caution and should be discussed with the doctor. These include:

  • Aneurysms
  • Cancer
  • Diabetes
  • Heavy menstrual periods
  • Hemophilia or other bleeding conditions
  • Kidney or liver disease
  • Sports
  • Stomach ulcers or other problems
  • Stroke or transient ischemic attack
  • Surgery (including dental surgery)