Anticoagulant prescription medications -- what many people call blood thinners -- can have serious side effects. For this reason, you may turn to over-the-counter supplements as a more natural way to reduce your blood's tendency to clot. Only vitamin E has possible blood thinning properties, and clinical studies on its effects have given mixed results. Because even vitamins can have serious side effects when taken in large doses, ask your doctor before taking vitamin E as an anticoagulant, and do not add it to your current medication regime without his approval.
Vitamin E, a fat soluble vitamin, may prevent blood clots from forming or may make the effects of prescription anticoagulants such as warfarin more powerful. Vitamin E in large doses may interfere with vitamin K, which helps blood clot, according to Michael Lam, M.D. This affect varies from person to person, says Lam, who recommends limiting vitamin E doses to 400 mg per day. Doses of 800 mg or more may increase bleeding time in people taking the anticoagulant warfarin, pharmacist Jon Horton reported in the February 1999 "American Family Physician." Ask your doctor before taking vitamin E supplements if you take any type of blood thinner or if you have a disorder that interferes with blood clotting.
A study conducted by researchers from Brigham and Women's Hospital published in the September 2007 issue of "Circulation" looked at the 39,876 women who took either 600 mg of vitamin E or placebo on alternate days over a 10-year period. Researchers found that women who took vitamin E reduced their risk of deep vein thrombosis or pulmonary embolism by 21 percent.
A March 1996 article in the "American Journal of Cardiology" by the University of California Davis found vitamin E did not increase clotting time in people taking warfarin. The study included just 21 people divided into a vitamin E group and a placebo group. According to the Truestar Health website, subjects took doses of up to 1,200 mg of vitamin E in this study.
Do not take vitamin E with other blood-thinning medications, including herbs such as garlic, ginger, licorice root, willow bark and ginkgo biloba, without your doctor's supervision, since you could develop excessive bleeding or easy bruising. You may need more frequent monitoring of your INR, or International Normalized Ratio, the standard measurement for the time it takes blood to clot. The normal INR is 1.0, but people who take anticoagulants should have a prolonged INR of between 2 and 3, to prevent their blood from clotting easily.