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1. Pain is the stimulation of nerve endings

Senior Lecturer in Clinical Pharmacology at the University of Aberdeen, Dr Mary Joan McLeod, defines pain as "the stimulation of the nerve endings, either due to swelling or release of prostaglandins (fatty compounds with hormone-like actions)".

2. Painkillers follow the same pathway but have different outcomes

Painkillers work on the same pathway to the pain, but they do so in slightly different ways.

Paracetamol is the most commonly used painkiller and is best for "mild to moderate pain", according to Dr McCleod. "It can act in the brain on the temperature centre to reduce temperature and it can also work at the nerve endings to reduce production of prostaglandins."

Paracetamol does not work as effectively on muscle inflammation (eg. a twisted ankle, period pain, etc) as aspirin and ibuprofen, both of which are classed as non-steroidal anti-inflammatory drugs (NSAIDs).

You can actually mix paracetamol with ibuprofen or paracetamol with aspirin to increase pain relief, but you must be alert to the dosage and absolutely avoid taking two paracetamol-containing products at the same time.

Interviews carried out by Sliced Bread revealed that cost was a big factor in dictating what painkiller people bought. This tended to lead consumers to buy supermarket own-brand paracetamol, or own-brand ibuprofen if it was a joint pain. One respondent highlighted the effect that her upbringing had on her choice: "When my mum had a sore head, she would take paracetamol and that's what she recommended me to take."

4. The price of painkillers varies wildly

It's no wonder that budget holds sway on painkiller choice. The price of branded paracetamol and ibuprofen products can be as much as three times the cost of the supermarket own-brand equivalent. Those claiming to be faster acting are usually more expensive and the price can be six or seven times as much if there is an added ingredient such as caffeine.

There is also a difference in cost between tablets and capsules (where the painkiller is in powder form and delivered via a plastic coating). Greg found that paracetamol capsules looked to be around two to three times the cost of tablets for pharmacy-own or supermarket-own, and he found one packet of supermarket own-brand ibuprofen that differed by a factor of 10 between tablet and capsule form!

5. The form your painkiller comes in affects absorption

Whatever form your pill is in, you are likely getting the same dose. However, what is in the tablet or capsule alongside the painkiller can affect the absorption rate.

Solid tablets take longer to be absorbed than capsules or liquid preparations. Caplets are somewhere between the two. They're solid, like tablets, but they have different make-up of 'excipients' – the inactive ingredients that can aid ingestion. One example is sodium bicarbonate which is paired with paracetamol for faster absorption.

Paracetamol on its own will actually only provide pain relief for 30-40% of those who take it for moderate to severe pain. The addition of caffeine raises the effectiveness by 10%, "as long as there's 100 milligrams of caffeine or more in the product," advises Dr Andrew Moore, a biochemist with decades' worth of experience researching painkillers.

However, rather than buying tablets or capsules with added caffeine, which will be more expensive than ones without, you could simply take your paracetamol with a cup of coffee.

Aspirin's effectiveness is around 25 - 30% and out of those who take Ibuprofen for moderate to severe pain around 50-60% will get good pain relief.

7. There is no scientific evidence that certain painkillers can target specific pain

So, bearing in mind the varying degree of effectiveness on joint and muscle pain between paracetamol and aspirin or ibuprofen, is there any hard evidence to suggest, as some of the branded products claim, that painkillers can target specific pain, such as headaches, knee injury or period pain?

"I'm not aware of it being backed up by the science, no," says Dr Moore. However, up to a point, he says he is relaxed about these claims. "People have got busy lives," he says, "they don't need to be pharmacologists." He adds: "I've come to accept that it's a good idea to help individual people, to direct them to effective analgesics [pain relief] for the pain that they are suffering from."

8. But find the painkiller that works for you

Even if you ignore the claims of targeting specific pain, your search for the right painkiller will still leave you choosing between a wide range of products.

Before Greg pulls together the pros and cons for listener Hannah, Dr Moore offers some advice that may surprise you.

"If there's something that really works well for anybody, that's perfect for them," he says. "We're not interested in the average. We're interested in the individual. Because, at the end of the day, people with pain just want the pain to go away."

Hear Greg's summary, and find out how it will affect Hannah's painkiller purchasing in the future, by listening here.

The information in this article was correct at the time of broadcast on 9 February, 2023.