All analgesic drugs (painkillers) are tested in standardised clinical studies of people with established pain following surgery, and often after removal of third molar (wisdom) teeth. In all these studies the participants have to have at least moderate pain in order for there to be a sensitive measure of pain-relieving properties. The Cochrane Library has 35 reviews of oral analgesic interventions, with 38 different drugs, at various doses involving 45,000 participants in about 350 studies. This overview sought to bring all this information together, and to report the results for those drugs with reliable evidence about how well they work or any harm they may do in single oral doses.
For some drugs there were no published trials, for some inadequate amounts of information, and for some adequate information but with results that would have been overturned by just a few unpublished studies with no effect. None of these could be regarded as reliable. However, amongst the data there were still 46 drug/dose combinations with reliable evidence.
No drug produced high levels of pain relief in all participants. The range of results with single-dose analgesics in participants with moderate or severe acute pain was from 70% achieving good pain relief with the best drug to about 30% with the worst drug. The period over which pain was relieved also varied, from about two hours to about 20 hours. Typically adverse event rates were no higher with analgesic drugs than with placebo, except often with opioids (for example, codeine, oxycodone) where more participants experienced them.
Commonly used analgesic drugs at the recommended or licensed doses produce good pain relief in some, but not all, patients with pain. The reasons for this are varied, but patients in pain should not be surprised if drugs they are given do not work for them. Alternatives analgesic drugs or procedures should be found that do work.