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. 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 or keeping the lungs open, for example.

Aspirin works by preventing 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. According to Vincent E. Pearson, Pharm.D., former clinical coordinator for drug information at Johns Hopkins, 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 in combination with other agents is still considered quite effective against migraine.
  
  
• Reduce swelling by inhibiting prostaglandins that respond to injury sites.
  
  
• Reduce risk of blood clots and second ischemic stroke. Aspirin inhibits prostaglandins that are responsible for platelets sticking together to form clots. For this reason, anyone who has had a stroke or a transient ischemic attack (TIA), atrial fibrillation (a heart rhythm abnormality that can induce blood clots) or other clotting disorder may be put on aspirin therapy, either alone or in combination with other anti-clotting medications, such as warfarin. (Aspirin has not been shown to be valuable for reducing risk of first stroke.)
  
  
• Reduce risk of first or second heart attack. The first major study of the effects of aspirin on heart attacks was the Physician's Health Study, organized by Dr. Charles Hennekens of Harvard University. This randomized study followed more than 22,000 healthy male physicians, ages 40 to 84, for about 4 years. It found that men who took low doses of aspirin (325 milligrams every other day) were found to have a 44 percent reduction in risk of a first heart attack, compared with men who did not take aspirin regularly. A similar study involving approximately 40,000 women has been undertaken. Other studies have shown that long-term use of aspirin can reduce the number of second heart attacks.
  
  
• Treat acute myocardial infarction. Heart attack patients who are treated immediately with aspirin have reduced risks for second heart attack and stroke.
  
  
• Potentially reduce the risk of colon cancer. Although the data are not consistent, there is some evidence that regular use of aspirin reduces the risk of developing colon cancer and precancerous polyps by up to 60 percent. Although the exact dosages required are not yet known, at least one study has found that just 80 milligrams of aspirin a day, the equivalent of one "baby aspirin," is enough to suppress production of certain prostaglandins suspected to be involved in tumor formation.
  
  
• Reduce risk of eclampsia in pregnant women who develop preeclampsia. Eclampsia is a serious disorder of pregnancy in which blood pressure soars, possibly causing seizures, coma or even death. Aspirin inhibits the prostaglandins responsible for raising blood pressure.