Weight and Emergency Contraception: A Narrative Review of BMI, Efficacy, and Access

Abstract

Background: Emergency contraception (EC) is a time-sensitive component of reproductive healthcare that prevents pregnancy after unprotected intercourse or contraceptive failure. Emerging evidence suggests that the effectiveness of some oral EC methods, particularly levonorgestrel (LNG), may be reduced among individuals with higher body weight or body mass index (BMI), raising important clinical and counselling considerations.
Methods: This narrative review synthesizes pharmacologic, clinical, and health services literature examining the relationship between body weight or BMI and emergency contraception effectiveness. A targeted literature search was conducted in PubMed, Google Scholar, and relevant guideline sources to identify studies on emergency contraception, body weight, BMI, levonorgestrel, ulipristal acetate, and intrauterine devices. A narrative approach was chosen due to heterogeneity in study design, outcome measures, and populations, and the limited number of randomized trials powered to detect pregnancy outcomes across BMI categories. Included sources comprised clinical trials, pooled analyses, pharmacokinetic studies, systematic reviews, and clinical guidelines addressing oral LNG, oral ulipristal acetate (UPA), and intrauterine device (IUD)–based emergency contraception; studies not relevant to EC efficacy, BMI, or access considerations were excluded.
Results: Evidence suggests that the effectiveness of oral LNG emergency contraception may be reduced at higher body weight or BMI, although findings are heterogeneous and remain subject to debate. Oral UPA and copper intrauterine devices appear less affected by body weight but are constrained by prescription requirements, cost, and clinical availability. Counselling is further complicated by gaps between available evidence, clinical guidance, and real-world access.
Conclusions: Body weight and BMI are relevant considerations in emergency contraception counselling, but should not be the sole determinants of method selection. Clinicians should engage in shared decision-making that incorporates available evidence, uncertainty in effectiveness estimates, and timing of intercourse, patient preferences, and access constraints to support equitable, weight-inclusive emergency contraception care.
Key messages
• Emergency contraceptive pill effectiveness may be reduced at higher BMI, particularly for levonorgestrel, though evidence remains heterogeneous.
• Ulipristal acetate and intrauterine devices are less affected by BMI but are limited by prescription, cost, and procedural access.
• Clinicians should incorporate BMI, timing, access, and patient preferences into shared decision-making rather than relying on a single EC option.
• Structural and legal barriers disproportionately affect higher-BMI patients and should be considered during counseling.