Summary of findings for the main comparison. NSAIDs compared to placebo for dysmenorrhoea.

NSAIDs compared to placebo for dysmenorrhoea
Population: women with primary dysmenorrhoea Setting: Outpatient Intervention: NSAIDs Comparison: placebo
Outcomes	Illustrative comparative risks* (95% CI)		Relative effect (95% CI)	No of studies	Quality of the evidence (GRADE)	Comments
	Assumed risk4	Corresponding risk
	Placebo	NSAIDs
Pain relief dichotomous data	180 per 1000	490 per 1000 (452 to 528)	OR 4.37 (3.76 to 5.09)	35 studies	⊕⊕⊝⊝ low1,2,3	—
All adverse effects	100 per 1000	125 per 1000 (110 to 144)	OR 1.29 (1.11 to 1.51)	25 studies	⊕⊕⊝⊝ low1,3	—
*The basis for the assumed risk is provided in a footnote. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; NSAID: nonsteroidal anti‐inflammatory drug; OR: odds ratio
GRADE Working Group grades of evidence High quality: Further research is very unlikely to change our confidence in the estimate of effect. Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low quality: We are very uncertain about the estimate.

¹Very poor reporting of study methods by over 75% of studies; high risk of attrition bias in several studies; over 60% of studies commercially sponsored.
 ²Substantial heterogeneity (I² = 53%) but direction of effect consistent.
 ³Some suggestion of publication bias, favouring small studies with positive findings for NSAIDs.
 ⁴The control group risks are calculated from median values in 31 studies of pain relief and 19 of adverse effects in a previous version of this review.