A first-of-its-kind study has found that paracetamol is just as good as a combination of more expensive medicines to treat pain from sprains and falls.
The study of 118 patients at Auckland City Hospital refutes millions of dollars worth of corporate advertising for costly branded anti-inflammatory and opioid painkillers.
It found that 59 patients who were just given paracetamol felt no more pain one and two hours later than another 59 patients who were given paracetamol, ibruprofen and codeine.
The patients who were given the triple whammy actually suffered more "adverse events" (14) than the group who just received paracetamol (5).
Only four of the paracetamol group required extra "rescue" pain relief, compared with five in the triple whammy group.
Supervising author Dr Peter Jones, director of the hospital's emergency medicine research group, said no one had ever done the study before because doctors had always assumed that a variety of painkillers would be more effective than one - and because most research was funded by drug companies.
"Most medical research is driven by people who are making a profit out of the research," he said.
"Our research group never do any company-sponsored research. It's much harder for us because we have to rely on public funding."
The research was funded by the Auckland District Health Board's A-Plus Trust and by a Morson-Taylor research grant from the Australasian College for Emergency Medicine.
He said the group could have compared any single painkiller against a batch of others, but chose paracetamol because it was the cheapest and had few side-effects.
"No one is making a lot of money out of paracetamol. It's off-patent and it's cheap," he said.
"Because of the marketing around this, people have believed that the combination is better than paracetamol for injury pain. The reality is that they all provide equivalent pain relief, but it's cheaper and there's fewer side-effects to use either paracetamol or an anti-inflammatory."
The study looked only at patients with injuries but no cuts - usually from accidents such as falls and sports injuries. The group make up about a quarter of emergency department patients.
"It's not the people that have a bone sticking out of their leg. They need to get intravenous or intranasal painkillers," Jones said.
To get into the study the patients had to have pain of at least "three out of 10", classed as moderate or severe pain. Jones said most people who had such accidents felt the pain for about two days until the body dealt with the injury naturally.
"The best thing people can do is rest, ice, compression, elevation. It's going to be sore for a couple of days and then it will be fine," he said.
He said American researchers were concerned about growing use of opioid painkillers such as codeine and tramadol, which can be addictive.
Ibuprofen, the other anti-inflammatory tested in the study, can cause stomach pains.
Jones said he came up with the idea of the study. The lead author was Auckland clinical pharmacist Jiayi Gong and the other authors were Gong's research supervisor at Monash University in Melbourne, Dr Carl Kirkpatrick, and an Auckland City Hospital emergency medicine nurse practitioner Margaret Colligan. The study appears in the Annals of Emergency Medicine.
• One group received only 1g of paracetamol. The other group received 1g of paracetamol plus 400mg of ibruprofen and 60mg of codeine.
• On a scale of pain from 1 to 10, paracetamol alone reduced pain by 1.6 points after one hour and the three-drug combination reduced pain by 2 points.
• After two hours, pain was reduced by 2.4 points by paracetamol alone and by 2.9 points with the combination.
• These differences were within the minimum detectable difference of 1.3 points on the 10-point scale.