Anticoagulants decrease the clotting ability of the blood and therefore help to prevent harmful clots from forming in the blood vessels. These medicines are sometimes called blood thinners, although they do not actually thin the blood. They also will not dissolve clots that already have formed, but they may prevent the clots from becoming larger and causing more serious problems. They are often used as treatment for certain blood vessel, heart, and lung conditions.

In order for an anticoagulant to help you without causing serious bleeding, it must be used properly and all of the precautions concerning its use must be followed exactly. Be sure that you have discussed the use of this medicine with your doctor. It is very important that you understand all of your doctor's orders and that you are willing and able to follow them exactly.

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For anticoagulants, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to an anticoagulant. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy—Anticoagulants may cause birth defects. They may also cause other problems affecting the physical or mental growth of the fetus or newborn baby. In addition, use of this medicine during the last 6 months of pregnancy may increase the chance of severe, possibly fatal, bleeding in the fetus. If taken during the last few weeks of pregnancy, anticoagulants may cause severe bleeding in both the fetus and the mother before or during delivery and in the newborn infant.

Do not begin taking this medicine during pregnancy, and do not become pregnant while taking it , unless you have first discussed the possible effects of this medicine with your doctor. Also, if you suspect that you may be pregnant and you are already taking an anticoagulant, check with your doctor at once. Your doctor may suggest that you take a different anticoagulant that is less likely to harm the fetus or the newborn infant during all or part of your pregnancy. Anticoagulants may also cause severe bleeding in the mother if taken soon after the baby is born.

Breast-feeding—Warfarin is not likely to cause problems in nursing babies. Other anticoagulants may pass into the breast milk. A blood test can be done to see if unwanted effects are occurring in the nursing baby. If necessary, another medicine that will overcome any unwanted effects of the anticoagulant can be given to the baby.

Children—Very young babies may be especially sensitive to the effects of anticoagulants. This may increase the chance of bleeding during treatment.

Older adults—Elderly people are especially sensitive to the effects of anticoagulants. This may increase the chance of bleeding during treatment.

Other medicines—Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. Many different medicines can affect the way anticoagulants work in your body . Therefore, it is very important that your health care professional knows if you are taking any other prescription or nonprescription (over-the-counter [OTC]) medicine,