Oral emergency contraception (EC), is commonly used after recent unprotected intercourse to avoid undesired pregnancy, but does not provide ongoing contraception. Rigorous data allow for use of intrauterine devices (IUDs) as both EC and ongoing contraception, but EC efficacy data on use of the etonogestrel (ENG) implant, is lacking. The CDC Selected Practice Recommendations for Contraceptive Use support initiation of the ENG implant if oral levonorgestrel (LNG) is given concomitantly for EC. This recommendation lacks supporting evidence and serves as a barrier to method initiation, as oral LNG is not typically available in clinics when clients desire an implant. Additionally, oral LNG efficacy decreases in higher body mass index (BMI) users and the role of BMI on efficacy with co-administered oral LNG and the ENG implant is unknown. As the ENG implant is also a synthetic progestogen with a rapid rise and consistent systemic levels, it could plausibly serve as stand-alone EC or increase the efficacy of oral LNG with co-administration. Moreover, the EC mechanism of action, which is related to ovulatory suppression with oral EC, may differ if the implant is initiated with or without oral LNG, impacting efficacy in mid cycle users. This study addresses the following research gaps around use of the ENG implant for EC that serve as barriers to provider comfort with these options: efficacy with and without oral LNG, efficacy differences by BMI, and ovulation frequency with and without oral LNG. The investigators propose a randomized, placebo-controlled, non-inferiority study to determine if the ENG implant alone is no worse than the ENG implant + oral LNG for EC, using a 3.5% non-inferiority margin. The investigators will include clients who present to Planned Parenthood Association of Utah clinics with report of unprotected intercourse within 72 hours who desire EC. Eligible EC clients interested in an implant with a negative pregnancy test will be allocated 1:1 to a study group: (1) ENG implant + oral LNG or (2) ENG implant + placebo. Our experienced research staff will follow up with participants for 4-week efficacy data as primary outcome. Our aims include: (1) To compare the efficacy of the ENG Implant + oral LNG to the ENG Implant + placebo for EC in 790 participants assessed by pregnancy status four weeks after implant placement, (2) To compare pregnancy risk by BMI category (the investigators anticipate half of the 790 participants will have a BMI ≥25) between and within the ENG Implant + oral LNG and the ENG Implant + placebo groups, and (3) To evaluate ovulation frequency within 5 days of insertion of ENG Implant + oral LNG or ENG implant + placebo in 202 participants who are mid cycle (day 7-14 post menses) at time of enrollment assessed by serum progesterone levels and urine fertility monitor results. Our short-term goal is to expand evidence on the efficacy of implant initiation with or without oral LNG to meet the needs of EC clients. Our long-term goals are to develop evidence-based clinical guidelines to inform global contraceptive practices, allow for equity in long acting reversible contraception counseling at the time of EC, and support reproductive autonomy for people to achieve to their life goals.