Ref (type)	Population	Outcome, Interventions	Results and statistical analysis	Effect size	Favours
Pain
Systematic review	42 women with primary dysmenorrhoea 2 RCTs in this analysis	Pain relief by subjective assessment 18/31 (58%) with low-frequency TENS 15/32 (47%) with placebo TENS or tablet	OR 1.8 95% CI 0.6 to 5.1		Not significant
Systematic review	20 women with primary dysmenorrhoea Data from 1 RCT	Pain relief with low-frequency TENS with placebo TENS or tablet Absolute results not reported	P <0.05	Effect size not calculated	low-frequency TENS
Need for additional medication
Systematic review	24 women with primary dysmenorrhoea Data from 1 RCT	Mean number of additional tablets of analgesic used 3.7 with low-frequency TENS 6.8 with placebo TENS or tablet	WMD –3.1 tablets 95% CI –5.5 tablets to –0.7 tablets Randomisation and blinding unclear	Effect size not calculated	low-frequency TENS