Updated December 16, 2014.

In terms of cost, availability, and usefullness, aspirin is one of the greatest triumphs of medical science. First isolated from willow bark hundreds of years ago, aspirin is now available as a simple over- the-counter formulation. Aspirin is effective as a pain killer, an anti-inflammatory, and has actions that provide protection against serious diseases like heart attack and stroke. While there is not yet a clear aspirin blood pressure connection, the protective benefits are so large that routine, daily administration of aspirin is now recommended by the American Heart Association as a standard component of maintaining a healthy heart.

How Aspirin Works

Aspirin is a type of chemical called a "salicylate." Simple salicylates have been used as pain and fever reducers since the time of the ancient Greeks, more than 1,500 years ago. While aspirin has a large number of potential actions in the body, those related to heart health are straight-forward and well-understood. In the body, aspirin inhibits the formation of chemicals called "prostaglandins" by blocking an essential enzyme needed for their formation. Among the many properties of prostaglandins is their ability to promote blood cells to stick together. Thus, by blocking the formation of prostaglandins, aspirin decreases the likelihood of blood clots forming in your blood vessels.

Since a large number of heart attacks and strokes are directly caused by small, spontaneously forming blood clots, the ability of aspirin to prevent the formation of these small clots means that heart attacks and strokes become less likely.

How Much Aspirin Should I Take?

Aspirin dosing varies greatly depending on the reason it is being taken.

Large doses are sometimes needed for pain relief or to control fever. owever, for the purpose of cardiovascular protection, much smaller doses are required. This is because aspirin exerts much of its prostaglandin blocking activity even at low doses, and it takes increasingly larger doses to realize smaller and smaller amounts of additional benefit.

The actual research regarding specific doses of aspirin is fairly complicated, but has yielded data that can be generalized into a few basic recommendations, including:

• Average recommended dose is around 75mg per day
• The maximum recommended daily dose is 325mg per day
• The risk of side effects is fairly constant between these two dosing values

Possible Side Effects of Aspirin

While aspirin is generally a very well-tolerated medicine, it does have the potential to cause side effects. The important side effects of aspirin are generally:

• Increased risk of bleeding
• Stomach or intestine irritation
• Toxicity

A small number of people have unusual toxic reactions to small doses of aspirin. While serious, these reactions are rare, very easily noticed (cramping, vomiting), and can be treated.

Who Should Take Aspirin

Aspirin has shown benefit in people with a wide variety of cardiovascular problems. People who should consider taking asprin include:

• People with a history of heart attack
• Women older than 65
• People who have had an occlusive stroke
• Anyone with moderate to high risk of heart disease

It is important to understand that while aspirin can help many people who either have, or are at risk for, cardiovascular disease, the details of your personal medical history might mean that aspirin isn't a good choice.

Who Shouldn't Take Aspirin

Because aspirin increases the risk of bleeding, the people who shouldn't take aspirin usually have some history of abnormal bleeding or some type of bleeding disorder. In addition to people with bleeding disorders, aspirin may not be a good choice in people with:

• Allergies to another aspirin-like medicine
• Asthma
• Kidney disease
• Ulcers
• Gout

Additionally, aspirin should never be given to children or teenagers who have fever or flu-like symptoms.

The Future of Aspirin

Despite the clearly demonstrated benefits of aspirin, it remains underutilized. In an attempt to increase the use of aspirin in patients, several governing medical bodies have been carefully reviewing their offical recommendations. In early 2007, the American Heart Association - in response to newly analyzed data - updated their offical recommendations to state that all women over 65 be considered for routine aspirin therapy.

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Burch, JW, Stanford, N, Majerus, PW. Inhibition of platelet prostaglandin synthetase by oral aspirin. J Clin Invest 1978; 61:314.
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Hennekens, CH, Sechenova, O, Hollar, D, Serebruany, V. Dose of aspirin in the treatment and prevention of cardiovascular disease: current and future directions. J Cardiovascular Pharmacology and Therapeutics 2006.}