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Data from a meta-analysis of two RCTs comparing the efficacy of ulipristal acetate (UPA) with levonorgestrel (LNG) for emergency contraception demonstrated that the risk of pregnancy was more than threefold for obese women compared with women with normal body mass index whichever EC was used. (1) When pregnancy rates were compared within the treatments, the relative risk (RR) of pregnancy was doubled when overweight women taking LNG were compared with normal or underweight women using LNG, whereas the risk was not different when such women taking UPA were compared. Obese women using LNG more than four times likely to conceive than were normal or underweight women. For UPA, when obese women were compared to normal/underweight women the RR of pregnancy was estimated to be 2.62 (95% CI, 0.89–7.00).(1) Recent publications have shed more light on the issue. A pooled analysis of four WHO studies on LNG-EC showed increased pregnancy rates among obese women (BMI> 30 kg/m2) compared to women with normal BMI. (2) Biological plausibility for the effect of obesity on LNG-EC is provided by a study among normal weight and obese women demonstrating significant differences in pharmacokinetics (PK) with the direction of changes correlating with the observed reduction in effectiveness of LNG-EC seen clinically.(3) These findings were confirmed in a more recent study on the effect of obesity on the PK of LNG-EC. The study also showed that, in contrast, concentrations of UPA were not significantly reduced among obese women. (4) UK guidance states that ‘Women should be informed that it is possible that higher weight or BMI could reduce the effectiveness of oral EC, particularly LNG-EC’.The latest US recommendation goes further stating: “Prescribe ulipristal acetate when possible because it is more effective than levonorgestrel at all times up to 5 days after unprotected intercourse and in women of all weights.” References 1. Glasier A et al. Contraception 2011; 84: 363-7 2. Festin et al. Contraception 2017; 94:289-94 3. Edelman AB et al. Contraception 2016;94:52-7. 4. Praditpan P et al. Contraception 2017;95:464-469