pain relievers

How Pain killers work

How pain relievers work

If you’ve ever stood in the pain reliever aisle in your local pharmacy or drugstore and been amazed at the choice of products, it might be a surprise to discover that oral analgesic products usually contain just one of the following types of pain and fever-relieving ingredients:

  • paracetamol (also called acetaminophen in some countries)
  • a non-steroidal anti-inflammatory drug (NSAID), like aspirin, ibuprofen, naproxen or diclofenac.

These analgesics may be combined with other ingredients, such as caffeine and codeine, which increase the pain relieving effects of paracetamol or NSAIDs. Sometimes, paracetamol and NSAIDs are combined with cold and flu ingredients, which help to ease symptoms such as congestion and a runny nose. It’s important, however, to know that paracetamol and NSAIDs work in different ways to relieve pain.

How paracetamol and NSAIDs work differently

Both paracetamol and NSAIDs are effective when it comes to relieving mild-to-moderate pain.1 But, although they both relieve pain, how they do it is quite different.

Paracetamol is believed to act primarily in the brain and seems to have an effect on many different ways we can feel pain.2 For example, paracetamol inhibits the production of pain and inflammation-causing chemicals called prostaglandins.2  Prostaglandins are found throughout the body, but paracetamol mainly works on those in the brain. Because of this, not only can it effectively relieve pain and fever, but it also has few side effects when taken at recommended doses. Paracetamol also has no effect on inflammation.2

NSAIDs, such as ibuprofen and aspirin, work differently than paracetamol. They also stop the production of prostaglandins, but they do this throughout the body, not just in the brain.2 Because of this, NSAIDs can affect prostaglandins that have other important roles in the body.2 These include prostaglandins that protect the lining of the stomach, and keep the kidneys working properly, our airways open and our blood clotting normally.2 So, while NSAIDs are good at easing pain by stopping the development of some prostaglandins, they can also have a negative effect on those prostaglandins that are needed to keep our bodies functioning as normal, even at over-the-counter (OTC) doses.

When NSAIDs are used for several weeks at the higher prescription doses you get from your doctor (not the lower dose, over-the-counter versions), they can also help reduce inflammation.1 If you do need to reduce inflammation, speak to your doctor or pharmacist.1

Because paracetamol and NSAIDs work differently to relieve pain, this leads to other important differences between these types of analgesic. For example, they can cause different side effects, interact with different medications (which can change the way your medication works) and may not be suitable for use by everyone. That’s why it’s important to always read the medication label, to make sure your pain reliever is right for you. To find out which pain reliever is the right choice for your needs, read the article Choosing the Right Over-the-Counter Pain Reliever.


  1. Martindale: The Complete Drug Reference. 36th Edition, March 2009.
  2. Australian and New Zealand College of Anaesthetists and Faculty of Pain Medicine. Acute pain management: scientific evidence. Third edition 2010. Available at