Ngai 2005

Methods	The pharmacy department in Queen Mary Hospital generated the randomisation sequence by computer programme. Drug package was prepared by the pharmacy department according to the randomisation list. Clinicians and participants were unaware of the drug assignment. The pharmacy kept the randomisation list and it was revealed only at the final analysis. LNG and placebo were supplied by the WHO. Placebo was identical in colour, shape and size to LNG
Participants	2071 healthy women aged > 16 years were recruited from 5 sites in China (Beijing, Hong Kong, Nanjing, Shanghai and Shenzhen). All women had regular menstrual cycles (every 24‐42 days) and requested EC within 120 h of a single act of unprotected intercourse; they were willing to abstain from further acts of unprotected intercourse and were available for follow‐up over the next 6 weeks. Exclusion criteria: post‐abortion or post‐partum women whose period had not yet returned, regular use of prescription drugs before admission to the study and intercourse during the treatment cycle > 120 h before admission into the study. Women satisfying these criteria were admitted into the study after they had given written informed consent. 2060 women into efficacy analysis, 2071 women into safety analysis
Interventions	LNG 0.75 mg, 2 doses, 24 h apart orally vs LNG 0.75 mg, 2 doses, 12 h apart
Outcomes	Observed number of pregnancies, side effects and changes in menstrual pattern
Notes	Loss to follow‐up: 24 h apart LNG 24/1044; 12 h apart LNG 29/1027 Protocol violations: 24 h apart 6/1020; 12 h apart 5/998 Observed pregnancy/expected pregnancy/total number of women: 24 h apart LNG 20/71/1038; 12 h apart LNG 20/74/1022
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"The pharmacy department in Queen Mary Hospital generated the randomization sequence by computer program."
Allocation concealment (selection bias)	Unclear risk	Allocation concealment method wasn't explained
Blinding (performance bias and detection bias) All outcomes	Low risk	"The levonorgestrel and the placebo was supplied by the World Health Organization. The placebo was identical in colour, shape and size to the levonorgestrel." "Both the clinicians and the participants were unaware of the drug assignment. The pharmacy kept the randomization list and it was revealed only at the final analysis."
Incomplete outcome data (attrition bias) All outcomes	Low risk	ITT analysis used
Selective reporting (reporting bias)	Low risk	Planned outcomes were reported
Other bias	Low risk	None reported