Blood flowing freely through your veins and arteries is one of the body's most important processes. Yet it's one many people think the least about, until something goes wrong and blood stops flowing normally. Pregnancy, dehydration, or just sitting or lying still for a long period of time can put a person at risk for dangerous blood clots.

Called deep vein thrombosis (DVT), these clots are created when certain types of blood cells, known as platelets, stick to damaged blood vessels in a vein deep inside the body. DVTs most often block blood flow in the lower leg and thigh, causing symptoms such as leg pain; swelling; and warm, red skin. However, a clot can break away, move to another part of the body, and block blood flow to a major organ. This is called an embolism and it can cause severe damage or even death.

Effective medications for deep vein thrombosis that help prevent clots from forming come with benefits and risks. “These medications are commonly called blood thinners, but they don’t actually thin the blood  the concentrations of blood cells don’t actually change,” explained Keith McCrae, MD, a physician in the department of hematologic oncology and blood disorders at the Cleveland Clinic in Ohio.

More precisely, medications for DVT work to change the clot formation process. “There are a number of clotting factors in the blood that are necessary for normal clot formation," Dr. McCrae said. "Blood thinners work by either inhibiting the function of one of these clotting factors or lowering levels of these clotting factors by 10 to 20 percent of their normal levels."

Blood Thinners to Treat Deep Vein Thrombosis

Drugs for DVT fall into one of two main categories: anticoagulants and antiplatelets. Anticoagulants interfere with chemical reactions in the body to lengthen the time it takes a clot to form. Anticoagulant medications for deep vein thrombosis include warfarin (Coumadin), dabigatran (Pradaxa), rivaroxaban (Xarelto), and apixaban (Eliquis). Antiplatelet drugs prevent platelets from clumping together and forming a clot. Antiplatelet medications include aspirin, clopidogrel (Plavix), prasugrel (Effient), and ticagrelor (Brilinta). 

Physicians may prescribe blood thinners if you have a blood clot or to help prevent blood clots if you're at risk. A number of conditions and situations can put you at risk for blood clots and therefore make you a good candidate for blood thinners for deep vein thrombosis. The more risk factors you have, the more likely your physician is to prescribe medications for DVT.

DVT risk factors include:

  • An inherited blood disorder that increases your risk for blood clots
  • Taking birth control pills
  • A history of DVT
  • Injury to a vein from trauma, such as surgery or a broken bone
  • Pregnancy and the postpartum period
  • Lying in bed for long periods of time
  • Long travel, involving sitting for an extended time
  • Cancer and cancer treatment
  • Older age (over 60)
  • A central venous catheter for medical treatment
  • Obesity
  • Smoking

How to Take Medications for Deep Vein Thrombosis: Concerns and Precautions

Dosing for blood thinners for DVT can vary. “Generally, people take Coumadin once a day, but the exact dose varies based on how 'thin' the blood is,” explained Akshay Khandelwal, MD, an interventional cardiologist at the Henry Ford Hospital in Detroit.

Physicians measure blood consistency with a test called an international normalized ratio (INR). “Newer blood thinners, including Xarelto, which is taken once a day, and Eliquis, which is taken twice a day, do not require INR tests,” Dr. Khandelwal said. This makes them more convenient for some people.

However, cautions and concerns surround the use of most blood thinners. Blood thinners for DVT can cause side effects, such as increased spontaneous bleeding or bleeding after an injury or accident. And all blood thinners need to be avoided in the first trimester of pregnancy.
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Drug interactions also are an issue. Some medications can increase the potency of Coumadin, and others can make the drug less effective. “Coumadin interacts with many medicines, including some antibiotics, most antifungal medications, and several statins,” said Brian Gage, MD, MSc, an internist, professor at the Washington University School of Medicine in St. Louis, and medical director of the Barnes-Jewish Hospital Blood Thinner Clinic. You'll also need to follow your doctor's recommendations about eating large portions of foods high in vitamin K, such as green leafy vegetables, because this vitamin interferes with Coumadin.

Leafy greens aren't a problem with other blood thinners, but those drugs have their own cautions. “The body metabolizes some of the newer blood thinners through the same pathways as other medications, such as ketoconazole, used to treat fungal infections, and the herb St. John’s wort,” McCrea said. “So the important take-home message is, tell your doctor about all prescription and nonprescription medications, supplements, and herbs you are taking before you start a blood thinner.”

Once you’ve begun medication for deep vein thrombosis, you might take your meds with meals or when you brush your teeth,“to establish a habit,” Dr. Gage suggested.

Above all, always follow label directions carefully and be sure to check in with your doctor as recommended.