Data sourcesThe Cochrane Database of Systematic Reviews on the Cochrane Library.Study selectionAll Cochrane reviews of RCTs between 1999 to 2015, conducted in adults examining the adverse events associated with single dose oral analgesics used for acute post-operative pain were considered.Data extraction and synthesisStudies were searched, reviewed and assessed independently by two reviewers and standard data items extracted. Methodological quality was assessed using criteria adapted from AMSTAR (Assessing the Methodological Quality of Systematic Reviews).ResultsData from 39 Cochrane reviews of 41 different analgesics or analgesic combinations involving a total of 350 studies involving 35,000 adults were included. Most analgesics were tested in a narrow dose range. For most NSAIDs, paracetamol (acetaminophen), and combinations not containing opioids, the rates of adverse events were similar to that of placebos (NSAID 3% - 44% vs 4 - 46%; paracetamol 7-18% vs 6-16%; combination 11-30% vs 6-48%). However, for higher dosages, like 1000 mg aspirin, 1000 mg diflunisal, and opioids or drug combinations containing opioids, there was a statistically significant difference in the incidence of adverse events reported (NNH 7.7(95%CI; 4.8 - 20) for 1000 mg aspirin; 7.5(95%CI; 4.8-17) for 1000 mg diflunisal; 3.5-8.6 for opioids and combinations). Serious adverse events were rare, occurring at about 1 in 3,200.ConclusionsDespite ongoing problems with the measurement, recording and reporting of adverse events in clinical trials and in systematic reviews, the large amount of information available for single oral doses of analgesics provides evidence that adverse events rates are generally similar with active drug and placebo in these circumstances, except at higher doses of some drugs, and in combinations including opioids.