Aspirin, in some form, has been used as a treatment for over 2,500 years. The famed Greek physician, Hippocrates in the 5th century B.C. used an extract from the bark of the willow tree to treat fever. The chemical involved, salacin, is a natural product that is converted into salicylic acid in the body.

At the end of the 19th century the German company, Bayer, began marketing a modified manufactured form, acetylsalicylic acid (otherwise known as aspirin), devised by chemist Felix Hoffman. The product turned out to be one of the most successful drugs in the history of the world.

For such a simple molecule it has some of the most amazing properties in the biochemical world.

Aspirin has few side effects at the proper dosage and is used to treat dozens of conditions, such as inflammation, heart disease, fever and - of course - headaches. How it does this is in one way well understood, in another way quite a mystery. It is known that when injury occurs to tissue, prostaglandins are released that generate signals down nerve cells to the brain. What happens then is less clear.

Prostaglandins not only contribute to the pain signal, but to the swelling that follows. But how exactly those conditions translate into something we perceive as pain is still a matter of leading edge research. What is ‘injured’ in the case of a headache is not known.

For decades it was believed that tension headaches, for example, were the result of muscle tension typically in the neck, back or face, hence the name. But contemporary research sees that as less likely. What’s more likely, according to the evidence, is that muscle tension is involved but the interaction of serotonin (a neurotransmitter) with nerve cells is more important.

Whatever the ultimate cause, aspirin works by suppressing the cells from making prostaglandins. It interferes with a enzyme (known by the acronym COX) needed to make them, by binding with it. Eventually the combination is filtered out by the kidneys and more aspirin is needed to continue the process.

One possible side effect is that aspirin may do its job too well and remove needed prostaglandins from the stomach, making the lining too thin and leading to stomach upset or even ulcers. Aspirin also interferes with the creation of blood clots (prostaglandins play a part there, too). That can be helpful when used to prevent heart attacks, but is not helpful when you receive a cut or get a bloody nose.

While generally safe, it is possible to overdose on aspirin. The effects are not the same as overdose from other drugs, but in large doses it can interrupt proper kidney function, for example. To combat these effects, drug companies have designed alternatives, such as ibuprofen, acetaminophen and naproxen.

It will continue to be a part of headache treatment for some time to come, though. Given the 80 billion tables per year that are consumed, the body of clinical evidence showing it is safe is very large. Used properly, and provided the patient isn’t excessively sensitive to some of its effects, it can be a valid part of a treatment regimen.

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