So when it comes to weight and birth control effectiveness, it is always important to compare the risks of unintended pregnancy against the advantages and disadvantages associated with a particular contraceptive method. In general, methods where contraceptive failure is more likely to occur in obese women than in women of normal weight include: oral contraceptives, the contraceptive patch, and Implanon/Nexplanon.
Want to learn more? See UpToDate's topic, "Contraception counseling for obese women," for additional in-depth medical information on counseling obese women about their contraceptive options and exploring how weight can contribute to contraceptive failure.
Edelman, Alison and Kaneshiro, Bliss. "Contraception counseling for obese women." UptoDate. Accessed: May 2011