How Aspirin Works

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Harvard Medical School
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How Aspirin Works

Heart and Circulatory
Aspirin — The Wonder Pill
How Aspirin Works
How Aspirin Works
The use of salicylates, the chemical root of aspirin, goes back to the 5th century B.C., when Hippocrates used the bark of the willow tree to treat fevers and pain. It's come a long way since.
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Reviewed by the Faculty of Harvard Medical School

How Aspirin Works

The use of salicylates, the chemical root of aspirin, goes back to the 5th century B.C., when Hippocrates used the bark of the willow tree to treat fevers and pain. Despite widespread use of willow bark, its active ingredient, salicin, wasn't discovered until 1828. In the 1830s, salicin was refined into two similar medicinal compounds, salicylic acid and sodium salicylate. Unfortunately, these remedies had side effects that made them unattractive as pain relievers, including nausea, ringing in the ears and severe stomach irritation.

In 1897, in an attempt to ease his father's suffering from rheumatoid arthritis, Felix Hoffmann, a chemist working for Bayer, discovered a milder formulation called acetylsalicylic acid (ASA). This compound was called "Aspirin" —"A" from acetyl, "spir" from the spirea family of plants from which salicin was derived and "in" referring to a common ending in drug nomenclature.

Aspirin was immediately heralded as an excellent medication for controlling fever and reducing pain, especially from arthritis and headache. Plus, in the 1950s, some physicians began to prescribe aspirin for prevention of heart attacks because of its observed blood-thinning ability. Remarkably, no one knew how aspirin worked.

In 1971, the mystery was, for the most part, solved by British pharmacologist John Vane. Although many scientists believe that there is still much to discover about aspirin, careful experimentation has revealed that aspirin controls body compounds called prostaglandins.

Prostaglandins are hormone-like substances produced in small quantities throughout the body. There are many different types of prostaglandins, and each performs a different function. Some cause inflammation, redness and swelling in response to an injury or illness. Others are responsible for the general "housekeeping" of the body — keeping things running smoothly by protecting the gastrointestinal lining, for example.

Aspirin works by decreasing the production of prostaglandins. Because prostaglandins are involved in so many different body functions, aspirin can have many different types of effects on the body, both positive and negative. Aspirin can:

  • Reduce fever by inhibiting prostaglandins that work to raise body temperature.
  • Relieve headache and other pain by inhibiting prostaglandins responsible for inflammation and by dampening pain sensations. Even with all the other treatments available, aspirin is still considered quite effective against migraine headaches and arthritis.
  • Reduce swelling by inhibiting prostaglandins that respond to injury sites.
  • Reduce risk of heart attack and ischemic stroke. Aspirin inhibits prostaglandins that are responsible for platelets sticking together to form blood clots. Aspirin or other types of platelet inhibitors are usually prescribed for patients who are known to have or are at risk of blockages in the blood vessels that supply blood to the heart (coronary artery disease). Patients who have had a stroke or transient ischemic attack (TIA, or "mini-stroke") will usually take aspirin or another anticlotting medicine to prevent future stroke.
  • Treat heart attacks (myocardial infarctions). Heart attack patients who are treated immediately with aspirin have better outcomes and a reduced risk of second heart attacks and strokes.
  • Potentially reduce the risk of colon cancer. Although the data are not conclusive, there is some evidence that regular use of aspirin reduces the risk of developing colon cancer and precancerous polyps. The optimal dosage required is not yet known, but at least one study has found that just 80 milligrams of aspirin a day, the equivalent of one "baby aspirin," is enough to reduce production of certain prostaglandins suspected to be involved in tumor formation.


How Aspirin Works   Aspirin Timeline
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Last updated October 16, 2008

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