Immediate contraceptive initiation, including start of a method before abortion completion, is a convenient option for women seeking abortion care. To evaluate the effect of systemic hormonal contraception initiation on medical abortion effectiveness and the safety of hormonal contraceptive methods following abortion. PubMed, Popline, Cochrane Library, and Clinicaltrials.gov. Studies that assessed medical abortion effectiveness after systemic hormonal contraception initiation and the safety of hormonal contraception initiation after abortion. Pregnant persons undergoing or who had recently undergone an abortion. Initiation of systemic hormonal contraception post abortion or on the day of the first pill of the medical abortion. We assessed study quality using the US Preventive Services Task Force evidence grading system. We created narrative summaries and calculated pooled relative risks when appropriate. We identified 16 studies for inclusion, 7 randomized controlled trials, and 9 cohorts. Nine studies assessed medical abortion effectiveness with hormonal contraception initiation and generally found no decreased risk of abortion success or increased risk of additional treatment. One fair-quality study reported a small increase in ongoing pregnancy rate with immediate depot medroxyprogesterone (DMPA) compared with delayed DMPA initiation (3.6% vs 0.9%, risk difference 2.7%, 90% confidence interval 0.4-5.6). We identified no bleeding-related safety concerns following hormonal contraception initiation after medical or surgical abortion. Pooled results were too imprecise to draw firm conclusions. Included studies were poor or fair quality and primarily in high-income or upper-middle-income settings. Abortion effectiveness did not differ between immediate vs delayed initiation of most systemic hormonal contraceptive methods after a first trimester medical abortion. However, immediate DMPA initiation did show increased ongoing pregnancy. Bleeding effects with hormonal contraception initiation postabortion appeared minimal. Initiating a hormonal contraceptive method after an abortion and as early as the same day as the first pill of the medical abortion is an option if contraception is desired. The slight increase in ongoing pregnancy with immediate DMPA initiation highlights the importance of information provision during contraceptive counseling.