A Cochrane review [Abstract] 1 included 67 studies with a total of 5 743 subjects. Significant benefit of aspirin over placebo was shown for aspirin 600/650 mg, 900/1 000 mg and 1 200 mg, NNTs for at least 50% pain relief over 4 to 6 hours were 4.2 (3.9 to 4.8), 3.8 (3.0 to 5.1) and 2.7 (2.0 to 3.8), respectively. Fewer participants required rescue medication with aspirin than with placebo over 4 to 8 hours postdose, but by 12 hours there was no difference.
The number of participants experiencing adverse events was not significantly different from placebo for 600/650 mg aspirin, but for 900/1000 mg the number needed to treat to harm was 7.5 (4.8 to 17). The most commonly reported events were dizziness, drowsiness, gastric irritation, nausea, and vomiting, nearly all of which were of mild to moderate severity.
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