Ref (type)	Population	Outcome, Interventions	Results and statistical analysis	Effect size	Favours
Pain
Systematic review	53 women with primary dysmenorrhoea 2 RCTs in this analysis	Pain relief, as measured by subjective assessment 30/53 (57%) with high-frequency TENS 8/53 (15%) with placebo TENS	OR 7.2 95% CI 3.1 to 16.5	Large effect size	high-frequency TENS
RCT Crossover design	26 women with primary dysmenorrhoea	Change in visual analogue scale pain score after treatment From 4.81 to 2.18 with TENS for 1 cycle From 4.44 to 3.07 with sham TENS for 1 cycle	P = 0.018	Effect size not calculated	TENS
Need for additional medication
Systematic review	32 women with primary dysmenorrhoea Data from 1 RCT	Proportion of women needing additional analgesics 22/32 (69%) with high-frequency TENS 28/32 (88%) with placebo TENS	OR 0.3 95% CI 0.1 to 1.1		Not significant
Systematic review	24 women with primary dysmenorrhoea Data from 1 RCT	Mean number of analgesic tablets taken each day 6.92 with high-frequency TENS 6.78 with placebo TENS	WMD +0.1 tablets 95% CI –2.1 tablets to +2.4 tablets Randomisation and blinding unclear		Not significant