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How NSAIDs work

WebMD Medical Reference
Medically Reviewed by Dr Rob Hicks

Nonsteroidal anti-inflammatory drugs are also known as NSAIDs, and may be recommended to help treat symptoms of headaches, sprains, arthritis, pain, period pain, fever and swelling.

Examples of NSAIDs include diclofenac, ibuprofen, naproxen, celecoxib, mefenamic acid, etoricoxib, indomethacin and aspirin.

Although NSAIDs can be very effective, there is a risk of side-effects including indigestion, stomach ulcers, allergic reactions and heart problems.

How do NSAIDs help relieve pain?

NSAIDs work on pain a chemical level. They block the effects of special enzymes - specifically COX-1 and COX-2 enzymes. These enzymes play a key role in making prostaglandins. By blocking the COX enzymes, NSAIDs stop your body from making as many prostaglandins. This means less swelling and less pain.

Most NSAIDs block both COX-1 and COX-2 enzymes. They include the over-the-counter drugs aspirin and ibuprofen.

Aspirin has some benefits that other NSAIDs do not. The main one is that aspirin works against the formation of blood clots. As a result you are less likely to form the clots that can cause heart attacks and strokes. Other NSAIDs do not have this effect.

COX-2 inhibitors are a newer form of prescription NSAID, such as celecoxib or etoricoxib. As you might predict, they only affect COX-2 enzymes and not COX-1.

What are the side effects from standard NSAIDs?

Most people who use NSAIDs don't have any serious problems with them. But for some people - especially those who need pain relief regularly - there can be problems.

When you swallow a pill, it affects your whole system, not just the part that hurts. So while an NSAID may do a good job of easing your pain, it may also be having other effects - some of them unwanted - in other parts of your body.

Gastrointestinal problems

The most common side effect is an upset stomach.

Why? NSAIDs prevent the creation of prostaglandins, the hormone-like chemicals that cause swelling and increase pain. But that's not all that prostaglandins do. There are actually many different types of prostaglandins in your body.

One type of prostaglandin helps protect the lining of the stomach and gastrointestinal (GI) tract. And the COX-1 enzyme helps make this prostaglandin. Since traditional NSAIDs block COX-1 enzymes, they slow down the manufacture of this prostaglandin. This is why some NSAIDs cause high rates of gastrointestinal problems. With its defences down, your GI tract becomes irritated and damaged by gastric acids. The risk of this can be reduced significantly by also taking a stomach acid suppressing drug called a proton pump inhibitor (PPI).

High blood pressure and kidney damage

How can NSAIDs affect your blood pressure? NSAIDs reduce the blood flow to the kidneys, which makes them work more slowly. When your kidneys are not working well, fluid builds up in your body. The more fluid in your bloodstream, the higher your blood pressure will be. It's that simple.

If you take NSAIDs in high doses, the reduced blood flow can permanently damage your kidneys. It can eventually lead to kidney failure and require dialysis.

Allergic reactions

NSAIDs can also cause extreme allergic reactions, especially in people with asthma. It’s not understood why. Many specialists recommend that people who have asthma stay away from any NSAID, especially if they have sinus problems or nasal polyps.

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