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This article was originally published at The Conversation. Written by Michael Vagg, Pain Specialist at Barwon Health.

If you’re anything like me, your medicine cupboard is chockers with various non-prescription pain remedies: liquids, pills, capsules, children’s painkillers, formulations that are “gentle on the stomach” and products that claim to target specific parts of the body.

So what’s the difference between these products, and how do you choose what’s best for different types of pain?

Paracetamol, aspirin and ibuprofen

According to the Bandolier league table of analgesics for acute pain, the three most common painkillers – paracetamol, aspirin and ibuprofen – are all reasonably effective.

By comparison, a 400mg dose of ibuprofen (two regular tablets or capsules) will produce 50% pain relief in two out of five cases of acute pain. Paracetamol at a dose of 1000mg (two of the usual-size tablets) will produce the same benefit in just over a quarter of cases, whereas aspirin at a dose of 600mg (two usual tablets) is effective in just under a quarter of cases.

The measure used to calculate these results is called the number needed to treat (NNT). This is based on a 50%-or-better reduction in pain due to the drug alone, in a clinical trial setting. This is a reasonably stringent requirement which translates to a pretty effective treatment in the real world, once you include placebo benefit and being able to use hot packs, ice or other first aid measures.

How do you choose between the big three?

It’s important to realise that these analgesic drugs are not diagnosis-specific. They no more target specific sources of pain than the fire sprinklers in a building target the fire.

They all act by interfering with important pain signalling molecules wherever they occur in the body. It may well be that there are more of these molecules being produced in areas that have been injured, but the image of a friendly drug floating through your system with a specific target in mind is completely fanciful. The drugs block these molecules wherever they find them.

Given there is little high-quality evidence on which to base your choice of over-the-counter analgesics for specific conditions, it makes sense to decide which potential side effects you want to avoid.

Sprains and strains

For musculoskeletal injuries such as sprains and strains, the site may be inflamed in the first few days after the injury, causing warmth, swelling, redness and difficulty using the injured area normally. If inflammation is clearly present you will probably find that ibuprofen or aspirin are better.

If you have pain but no inflammation, paracetamol is likely to be as good as the other two.

Rest, ice and immobilisation are likely to be more helpful than any medication for acute muscle or tendon injuries.

Acute back pain tends to respond poorly to most medications, including prescription drugs. If one of the big three seems clearly better than the others for your flareup of back pain you should stick with it, but for most people none of them are much help in the early stages of the pain.

Dental pain

For pain following a dental procedure or other minor surgery, ibuprofen has the edge in effectiveness, but at the expense of potential increased bleeding complications if you take too much.

Both aspirin and ibuprofen inhibit the stickiness of platelets in your blood and make it less able to clot.

Aspirin and ibuprofen may have an advantage in diagnosed migraines, but any of the three in combination with codeine will potentially cause rebound headaches if used more than couple of times a week.
Image: Jandrewnelson / Wikimedia Commons

Headaches

Headaches represent a particular problem. True migraine headaches respond better to aspirin and ibuprofen than paracetamol.

Tension type headaches can respond to any of the three and are the commonest type of recurrent headache. But frequent use of paracetamol, especially in combination with codeine and doxylamine succinate, is associated with the phenomenon of rebound headache.

Aspirin and ibuprofen by themselves are less likely to cause worsening headaches, but produce more side effects on the kidneys and gastrointestinal tract with regular use. Combined with codeine, they are as bad as paracetamol.

The moral of the story with headaches is to avoid taking non-specific medications more often than a couple of times a week, and look for non-pharmacological ways of reducing the frequency of your headaches.

Period pain

Period pain is an instance where there is some evidence to prefer ibuprofen or one of its anti-inflammatory cousins to aspirin or paracetamol.

As always, the duration of medication use and the dose should be kept as low as possible to get the job done.

Cold and flu

Cold and flu tablets mostly have paracetamol as the analgesic component, probably because of its ability to reduce fevers.

There is conflicting evidence that treating fevers due to acute infections is always a good idea. The system by which the body produces a fever is complex, and very strongly conserved throughout evolution, and there is still no clear demonstrated benefit for suppressing it. So save the paracetamol or aspirin for when the infection is causing symptoms such as headache or muscle pain which might warrant its use.

Painkillers for children

Paracetamol has some clear safety advantages in children. Aspirin use among children can trigger a nasty problem called Reye’s syndrome which has an unknown mechanism and is potentially fatal due to liver and brain damage. The occurrence of Reye’s syndrome in Australia has thankfully plummeted since aspirin was banned for use in children some years ago.

Ibuprofen, in recommended doses, does not seem to trigger Reye’s syndrome despite its mechanism of action being almost identical to aspirin. Ibuprofen, however, needs to be used with caution in children who have unpredictable asthma as it may trigger attacks.

Dosing of over-the-counter analgesics (and almost all other drugs) in children needs to be done very strictly in accordance with the recommendations on the label. Read them very carefully and follow the dose guidelines meticulously.

Fatal cases of liver damage in children have occurred with paracetamol where adult doses have been used inappropriately, and cases of kidney failure have occurred where the same has been done with ibuprofen.

Fine print

No matter what the label may say, these drugs are not diagnosis-specific, so choose your over-the-counter painkiller based on the side affects you want to avoid as much as what your pain is.

Finally, it’s important to stick meticulously to the recommended doses on the label. These have been chosen after enormous research and experience to be the doses which best combine effectiveness with safety.

Michael Vagg has received honoraria (when he remembers to submit the invoices) for speaking at educational events sponsored by companies whose product range includes OTC painkillers. No direct conflict of interest is present for the subject of this article.

This article was originally published at The Conversation.
Read the original article.