Bednarek 2013.

Methods	Location: Portland Oregon, USA Recruitment time: December 2010 to June 2011 Sample size calculation and the outcome of focus: Assuming one‐sided alpha of 0.05, pooled SD 28 mm and power 82%, a sample size of 12 in each group was calculated to detect 30 mm pain score difference between groups.
Participants	General with N: 24 nulliparous women Source: academic medical clinic and local family planning clinic Inclusion criteria: nulliparous women, age 18 to 45 years, requesting LNG‐IUS for contraception Exclusion criteria: previous pregnancy > 20 weeks; previous IUD placement or attempted placement; contraindication to nitroprusside or LNG‐IUS; history of migraine, cluster or vascular headaches; blood pressure < 90/55 or > 150/100 at beginning of study visit
Interventions	1) 10 mg nitroprusside, 1% aqueous gel 2) Placebo gel Timing: immediately prior to IUD placement
Outcomes	Primary: pain score at tenaculum placement, with IUD insertion, and 30 min post‐insertion (100 mm VAS with 0 = no pain and 100 = worst imaginable pain) Secondary: side effects, satisfaction (100 mm VAS)
Notes	IUC used: LNG‐IUS
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated randomization list, source not specified
Allocation concealment (selection bias)	Low risk	Study drug prepared and packaged at a separate site
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Participants and all study staff involved in the care of the participant were blinded to study arm allocation.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Loss to follow‐up: none