What You Need to Know About Blood Thinners

8 million Americans take medication to dissolve or prevent blood clots

Liz Szabo,

AARP

Reviewed by

Merle Myerson, M.D.

Comments

Published November 15, 2024

pill bottle with red blood cell background

Photo Collage: AARP; (Source: Getty Images (2))

Tina Ridler knew something was wrong last October when her right leg became swollen, achy and hot.

Her doctor suggested she go to the emergency department for a scan, where an ultrasound showed a large blood clot, which forms when components of the blood (red blood cells, platelets and protein strands called fibrin) clump together.

This kind of blood clot in the legs, also known as a deep vein thrombosis, can be a medical emergency. Clots can travel to the lung and cause a pulmonary embolism, a potentially fatal complication that prevents blood and oxygen from flowing through the lungs, says Karol Watson, M.D., a cardiologist and professor of medicine at the David Geffen School of Medicine at UCLA.

Blood clot symptoms

Not everyone who has a blood clot experiences symptoms.

If you have a blood clot in your leg or arm, you may notice:

Swelling
Pain or tenderness
Warmth
Redness or discoloration

Signs of a pulmonary embolism can include:

Difficulty breathing
Faster than normal or irregular heartbeat
Chest pain or discomfort, which usually worsens with a deep breath or coughing
Cough or coughing up blood
Very low blood pressure, lightheadedness, or fainting

These signs and symptoms warrant immediate medical attention.

Source: U.S. Centers for Disease Control and Prevention (CDC)

Clots can form in other locations, as well. If clots lodge in arteries that supply blood to the heart, they can cause heart attacks. If they get stuck in a blood vessel leading to the brain, they can cause strokes.

Ridler’s doctors prescribed a fast-acting blood thinner, called a direct oral anticoagulant, to break up her clot quickly.

“When doctors saw my scan, they said, ‘Take this immediately,’” recalls Ridler, 59, who runs a wellness company in Rochester, Minnesota. The feeling she got was that “the clock was ticking.”

Every year, up to 900,000 Americans develop a blood clot, according to the Centers for Disease Control and Prevention, including 60,000 to 100,000 people who die from them. Older adults have a greater risk of developing one.

Clotting is a balancing act. For example, the body forms clots when someone cuts their finger in order to stop the bleeding. The clotting process helps create a scab over the wound to protect the body from germs and dirt. If blood didn’t clot in response to an injury, a person could bleed to death. As an injury heals, the body naturally dissolves the clot.

Sometimes, as in the case with deep vein thrombosis, clots form inside the blood vessels even if no injury has occurred, and they don’t dissolve on their own. When a blood clot forms in a vein, it can block the flow of blood as it travels back to the heart. This causes blood to accumulate behind the clot and build up pressure, resulting in the sort of pain and swelling that Ridler experienced in her leg.

Blood thinners can help prevent, treat blood clots

Doctors prescribe two major types of medications to combat blood clots — antiplatelets and anticoagulants — and an estimated 8 million Americans take them.

Antiplatelet medications, such as clopidogrel and aspirin, are mainly prescribed for people who have had a heart attack or a stroke. These drugs work by preventing platelets — cell fragments in the blood that stop or prevent bleeding — from sticking together to form clots at times when clotting is not needed, says Darae Ko, M.D., an assistant professor of medicine at Harvard Medical School and the Marcus Institute for Aging Research/Hebrew SeniorLife in Boston.

Anticoagulants (warfarin, heparin and a newer class of drugs called direct oral anticoagulants) work by interfering with proteins involved in the clotting process. Doctors prescribe them to dissolve or prevent large clots, Ko says. Someone who has a higher risk of blood clots due to another health condition, such as atrial fibrillation, may be prescribed an anticoagulant.

Anticoagulants can be injected, given by IV or taken as pills.

A closer look at anticoagulants

Risk factors for blood clots

Almost anyone can have a blood clot, but there are some factors that can increase your risk, including:

Injury to a vein, caused by a fracture or surgery, for example
Slow blood flow, often caused by paralysis or limited movement
Increased estrogen
Chronic health conditions like heart disease, lung disease, cancer and inflammatory bowel disease
An inherited clotting disorder
Age (risk increases with age)
Family history
Obesity
Traveling for long periods of time (generally more than four hours) — especially if a person has other blood clot risk factors. Getting up and moving can help lower this risk.

Source: U.S. Centers for Disease Control and Prevention (CDC)

Heparin is one of the oldest anticoagulants and is given either by injection or through an IV line. It’s often given to hospital patients with clots because it starts working very quickly. Doctors may also prescribe heparin to prevent blood from clotting, Ko says.

Warfarin, also known as Coumadin, has been used since the 1940s. This pill prevents the body from using vitamin K — a key ingredient in the clotting process. It generally takes about three days for warfarin to take effect. However, it can take longer — sometimes several weeks — for your doctor to make sure that the dose you are taking results in the correct level in your blood.

Regular blood tests — known as a PT INR — are needed to check this level. If your dose is too high, it can lead to severe bleeding, especially in the digestive tract, Ko says. If the dose is too low, the medication won’t be effective at preventing clots.

Warfarin wears off slowly, which is why if you are having a procedure or an operation, you may be asked to stop the drug several days beforehand. Some patients require coverage with another medication when they stop warfarin, especially if they are at higher risk for clots.

Many foods, medications and dietary supplements — including alcohol, over-the-counter pain relievers, green tea, gingko and certain fruits and vegetables — affect the way warfarin works. People who take warfarin should talk to their doctors about what medications and food to avoid, and how to manage their diet, Ko says.

Direct oral anticoagulant drugs are relatively new. The Food and Drug Administration approved the first of these pills, dabigatran, in 2010. Other drugs in this class soon followed. Clinical trials have found that these drugs work as well or better than warfarin to prevent clots, but are much safer, with a lower risk of bleeding.

The American Heart Association now recommends these drugs for most people with atrial fibrillation who need anticoagulants, with the exception of people with certain conditions. These pills are also easier to take because people don’t need routine blood tests and don’t need to restrict their diets, Ko says. Because of these advantages, the vast majority of people taking anticoagulants now use these drugs.

However, direct oral anticoagulants can be pricey. A 30-day supply of Eliquis has a list price of nearly $600 a month, compared to $2.22 a month for warfarin. When selecting the first 10 drugs to be included in Medicare price negotiations, the Centers for Medicare & Medicaid Services selected two direct oral anticoagulants — Eliquis and Xarelto — because of their high prices and large volume of prescriptions.

5 health conditions that can increase your blood clot risk

1. Atrial fibrillation is an irregular heart rhythm that occurs when the electrical signal that initiates the heartbeat (in the right upper heart chamber) is disrupted and taken over by other areas in the heart. This results in blood not flowing smoothly through the heart, which can lead to clots that may be carried to other areas of the body, such as the brain.

2. Heart valve surgery or replacement can cause clots to form at the site of the new valve, says Ifeoma Onuorah, M.D., a cardiologist and assistant professor at the Emory University School of Medicine and a member of the American College of Cardiology’s prevention council. The risk generally tends to be greater with mechanical heart valves than with tissue valves.

3. Hip or knee replacement increases the risk of clots forming in veins of the leg. Blood thinners may be given for a short period to patients recovering from these procedures, often before they can get up and walk around.

4. Cancer. About one in 10 people with cancer develop a blood clot, the second-leading cause of death in people with cancer.

5. Blood clotting disorders, some of which are inherited.

Side effects of blood thinners

Because blood thinners increase the risk of bleeding, people taking them need to take extra care to avoid cuts and bruises, Onuorah says. If people taking blood thinners fall or hit their head, they need to “call their doctor or call 911 because we need to make sure that there is no bleeding in the brain.”

Blood thinners can be risky or dangerous for some people, including those with disorders that cause them to bleed heavily. Frail people with a high risk of falling also face greater risk, Ko says.

“When I have an 80-year-old patient who comes in with their family member and they have to be on a blood thinner,” Ko says, “I do talk a little bit about making sure that the environment they're in is safe and that there's nothing that will put them at risk of fall.”

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