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Aspirin vs. Warfarin (Coumadin, Jantoven) Side Effects & Dosages

Aspirin vs. warfarin (Coumadin, Jantoven)

What is aspirin? What is warfarin (Coumadin, Jantoven)?

Aspirin is a nonsteroidal anti-inflammatory drug (NSAID) used to treat fever, pain, and inflammation. It is also used to prevent blood clots (antithrombotic). Other NSAIDs include ibuprofen (Motrin), nabumetone (Relafen), and indomethacin (Indocin). NSAIDs reduce levels of chemicals called prostaglandins that are released when there is inflammation. NSAIDs block cyclooxygenase, the enzyme that makes prostaglandins, resulting in lower concentrations of prostaglandins and reduction of inflammation, pain, and fever. Prostaglandin inhibition also reduces the blood’s clotting ability so aspirin is also used to reduce the risk of another stroke or heart attack in people who have already had a stroke or heart attack.

Warfarin (brand names Coumadin, Jantoven) is an oral anticoagulant that prevents the formation of blood clots by reducing the production of factors by the liver that promote clotting: factors II, VII, IX, and X, and the anticoagulant proteins C and S. The production of these factors by the liver depends on adequate amounts of vitamin K. Warfarin antagonizes vitamin K and reduces the production of these factors. Warfarin is used to treat deep vein thrombosis (DVT), to prevent further emboli in patients with pulmonary embolism, to reduce the risk of strokes and after a heart attack in patients with atrial fibrillation or artificial heart valves, to prevent blood clots from forming in certain orthopedic surgeries, and to prevent closure of coronary artery stents due to clotting.

What are the side effects of aspirin and warfarin?


Most patients benefit from aspirin and other NSAIDs with few side effects. However, serious side effects can occur and generally tend to be dose-related. Therefore, it is advisable to use the lowest effective dose to minimize side effects.

The most common side effects of aspirin involve the gastrointestinal system and ringing in the ears.

Gastrointestinal side effects are

  • ulcerations,
  • abdominal burning,
  • pain,
  • cramping,
  • nausea,
  • gastritis, and
  • even serious gastrointestinal bleeding and
  • liver toxicity.

Sometimes, ulceration and bleeding can occur without any abdominal pain. Black tarry stools, weakness, and dizziness upon standing may be the only signs of internal bleeding.

Ringing in the ears

  • Should ringing in the ears occur, the daily dose should be reduced.

Other side effects include:

Other side effects and adverse reactions

  • Aspirin should be avoided by patients with peptic ulcer disease or poor kidney function, since this medication can aggravate both conditions.
  • Aspirin may exacerbate asthma.
  • Aspirin can raise the blood uric acid level and is avoided in patients with hyperuricemia and gout.
  • Children and teenagers should avoid aspirin for symptoms of the flu or chickenpox because of the associated risk of Reye's Syndrome, a serious disease of the liver and nervous system that can lead to coma and death.
  • Aspirin can increase the effect of medicines used to treat diabetes mellitus, resulting in abnormally low blood sugars if blood sugar levels are not monitored.
  • NSAIDs should be discontinued prior to elective surgery because of a mild tendency to interfere with blood clotting. Aspirin, because of its prolonged effect on platelets, is best discontinued at least ten to fourteen days in advance of the procedure.


The two most serious side effects of warfarin are:

  • Bleeding
  • Necrosis (gangrene) of the skin

Bleeding can occur in any organ or tissue. Bleeding around the brain can cause severe headache and paralysis. Bleeding in the joints can cause joint pain and swelling. Bleeding in the stomach or intestines can cause weakness, fainting spells, black tarry stools, vomiting of blood, or coffee ground material. Bleeding in the kidneys can cause back pain and blood in urine.

Other side effects include:

Signs of overdose include bleeding gums, bruising, nosebleeds, heavy menstrual bleeding, and prolonged bleeding from cuts.

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What is the dosage of aspirin vs. warfarin?


  • Aspirin should be taken with food. Doses range from 50 mg to 6000 mg daily depending on the use.
  • Usual doses for mild to moderate pain are 350 or 650 mg every 4 hours or 500 mg every 6 hours.
  • Doses for rheumatoid arthritis include 500 mg every 4-6 hours; 650 mg every 4 hours; 1000 mg every 4-6 hours; 1950 mg twice daily.
  • Heart attacks are prevented with 75, 81, 162 or 325 mg daily.
  • 160 to 325 mg of non-enteric coated aspirin should be chewed immediately when experiencing symptoms of a heart attack.
  • The dose for preventing another stroke is 75 to 100 mg daily.


  • Warfarin may be taken with or without food.
  • Since warfarin is metabolized (inactivated) by the liver and then excreted by the kidneys, dosages need to be lowered in patients with liver and kidney dysfunction.
  • Frequent blood tests (INR test) are performed to measure the effect of warfarin and to adjust dosing.
  • There are published INR ranges for the various uses of warfarin.
  • Treatment usually is started at 2 to 5 mg once daily and the dose is adjusted based in INR tests.
  • Patients typically require 2 to 10 mg of warfarin daily.


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What drugs interact with aspirin and warfarin?


  • Aspirin is associated with several suspected or probable interactions that affect the action of other drugs. The following examples are the most common of the suspected interactions.
  • NSAIDs may increase the blood levels of lithium (Eskalith, Lithobid) by reducing the excretion of lithium by the kidneys. Increased levels of lithium may lead to lithium toxicity.
  • Aspirin may reduce the blood pressure lowering effects of blood pressure medications. This may occur because prostaglandins have a role in the regulation of blood pressure.
  • When aspirin is used in combination with methotrexate (Rheumatrex, Trexall) or aminoglycoside antibiotics (for example, gentamicin) the blood levels of the methotrexate or aminoglycoside may increase, presumably because their elimination from the body is reduced. This may lead to more methotrexate or aminoglycoside-related side effects.
  • Individuals taking oral blood thinners or anticoagulants, for example, warfarin, (Coumadin) should avoid aspirin because aspirin also thins the blood, and excessive blood thinning may lead to serious bleeding.


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Are aspirin and warfarin safe to use while pregnant or breastfeeding?


  • Aspirin is generally avoided during pregnancy because it may adversely affect the fetus. However, low aspirin doses have been safely used for the prevention of complications of pregnancy.
  • Aspirin is excreted into breast milk and may cause adverse effects in the infant.


  • Warfarin should be avoided by pregnant women or women who may become pregnant. Birth defects and fetal bleeding have been reported.
  • Available evidence suggests that warfarin is not secreted in breast milk.

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