Blood thinners prevent blood clots, which can stop blood flow to the heart. Learn about how they work, who should take them, side effects, and natural remedies.

Blood thinners are medications taken orally or intravenously (through a vein) to prevent a blood clot. Blood clots stop the flow of blood to the heart, lungs, or brain. They can cause a heart attack or stroke.

Your doctor may recommend taking a blood thinner if you have heart disease, including heart valve disease and irregular heart rhythms.

Blood thinners must be taken exactly as directed. When you don’t take enough, the medication won’t be as effective. Taking too much can lead to severe bleeding.

What Blood Thinners Do

Some blood thinners thin the blood to keep blood cells from sticking together in the veins and arteries. Others prevent blood clots by increasing the amount of time it takes for blood clots to form.

Antiplatelet drugs prevent blood cells (called platelets) from clumping together and forming clots. Examples of antiplatelet drugs are:

Doctors often prescribed medications called anticoagulants to people who have been diagnosed with some forms of heart disease. “Coagulate” is a medical term that means “to clot.” These blood thinners prevent blood clots by increasing the amount of time it takes your blood to clot.

Anticoagulants prevent clots from forming. Common anticoagulant blood thinners include:

  • warfarin (such as Coumadin and Jantoven)
  • enoxaparin (such as Lovenox)
  • heparin

Newer anticoagulants with less risk of bleeding include:

Your doctor will carefully monitor your dosage of blood-thinning medication. They may occasionally run a prothrombin time test (PT) for some medications. This blood test measures your international normalized ratio (INR).

INR is the rate at which your blood clots. An appropriate INR rate varies from person to person according to their medical history. Staying within your INR range can prevent you from bleeding excessively or clotting too easily.

Drug Interactions

Various foods, herbs, and medications can interfere with blood thinners. These substances can make the drug more or less effective than your dosage would suggest. However, not all blood thinners are affected by the same substances. It’s important to speak with your doctor or cardiologist about your diet and how it may impact the effectiveness of your medication.

Vitamin K

Vitamin K can lessen the effectiveness of some anticoagulants, such as warfarin. Depending on the particular medication you’re taking, you may still be able to eat foods with low to moderate levels of vitamin K. However, you should avoid eating certain foods that contain moderate to high levels of vitamin K. These include:

  • cabbage
  • Brussels sprouts
  • broccoli
  • asparagus
  • endive
  • kale
  • lettuce
  • spinach
  • mustard greens
  • turnip greens
  • collard greens


People who take anticoagulant medications should use herbal supplements and teas with caution. Several herbs interfere with the anti-clotting abilities of blood thinners. They can also increase your risk of bleeding and the amount of time you bleed.

Talk to your doctor before using any herbal supplement or tea, especially the following:

  • chamomile
  • echinacea
  • clove
  • evening primrose oil
  • dong quai
  • licorice
  • ginseng
  • gingko biloba
  • goldenseal
  • willow bark

Alcoholic beverages and cranberry juice can also be harmful when using blood thinners. Avoid these items as much as possible.


Take prescription and over-the-counter medications with caution when you’re using blood thinners. A number of antibiotics, anti-fungal drugs, pain relievers, and acid reducers can increase your risk of bleeding. Other drugs, including birth control pills, can decrease the effects of anticoagulants and increase your risk of developing a blood clot. Make sure to tell your doctor about all the medications you’re taking.

Side Effects

Blood thinners may cause side effects in some people. Excessive bleeding is the most common reaction. It can occur in a variety of ways, including:

  • heavy periods
  • bloody or discolored urine or feces
  • nosebleeds
  • bleeding gums
  • prolonged bleeding from a cut

Other side effects can include:

  • dizziness
  • muscle weakness
  • hair loss
  • rashes

The presence of blood thinners in your system can increase your risk of internal bleeding after an injury. Go to the hospital right away if you experience any of these side effects after falling or bumping your head — even if you don’t have external bleeding.

Your doctor may tell you to limit your participation in contact sports to reduce the risk of bleeding. However, this doesn’t mean you can’t exercise or live a normal life. Swimming, walking, and jogging are excellent forms of exercise and are safe for most people taking anticoagulants. Discuss with your doctor which types of exercise may be best for you.

Tell your dentist that you’re taking blood thinners to avoid excessive bleeding during regular teeth cleanings.

It’s also important to protect yourself when using knives, scissors, or yard equipment.

Natural Blood Thinners

Certain foods and herbs are natural anticoagulants and can help prevent your blood from clotting. These include:

  • garlic
  • ginger
  • celery seed
  • aniseed

Foods rich in vitamin E are also natural blood thinners. A number of oils contain vitamin E, such as olive, corn, soybean, and wheat germ. Other food sources of vitamin E include:

  • spinach
  • tomatoes
  • mangoes
  • kiwis
  • peanut butter
  • almonds
  • sunflower seeds
  • broccoli

Natural anticoagulants can be beneficial to your heart health, but consume them with caution. Check with your doctor before eating these foods if you’re taking a blood-thinning medication.