Adolescent pregnancy is a major public health issue with profound implications for health and socioeconomic factors. The use of long-acting reversible contraception (LARC) could be an interesting strategy to reduce the unintended pregnancy rate. However, the cost of LARC is still a barrier to widespread adoption. This study aimed to analyze the effectiveness and economic impact of long-acting reversible contraception (LARC) compared to non-LARC methods in preventing unintended pregnancy among adolescent girls. This systematic review was registered in PROSPERO (CRD42023387735) and conducted following the PRISMA guidelines. We included articles covering adolescents aged 10 to 19 years without language restrictions that evaluated the use of LARC compared to non-LARC on effectiveness and public health costs of unintended pregnancy. The search for articles included the databases MEDLINE/Pubmed, Cochrane Library, Embase, and Lilacs, using the entry terms "Adolescent" and "Long-Acting Reversible Contraception". We evaluated the risk of bias and the certainty of the evidence for each outcome of interest. The search retrieved a total of 1,169 articles and, after the title and abstract, we identified 40 articles for full-text analysis. Out of the 40 studies evaluated, four articles met the eligibility criteria for cost evaluation, and one met the eligibility criteria for effectiveness as an outcome. In conclusion, LARC emerges as the most effective and cost-effective contraceptive method. The cost of utilizing LARC, especially the copper IUD, is significantly lower than the costs attributable to unintended pregnancies in adolescence.