BackgroundAdolescence is the most crucial part of life. The vulnerability of adolescent mothers is even more pronounced and can affect various health aspects. While they suffer from social and emotional stresses shortly after giving birth, the long-term effect after the post-partum period of adolescent pregnancy on the mental outcomes holds prime importance. Thus, this systematic review aims to ascertain the association between adolescent pregnancy on mental health outcomes.MethodsThe search strategy was run in June 2023 on databases including PubMed, CINAHL, Scopus, Psych Info, and Embase . Quality assessment of the studies was done using the National Institute of Health (NIH)'s National Heart, Lung and Blood Institute (NHLBI) tool for observational studies. For studies that measured similar outcomes, a meta-analysis was conducted.FindingsThe search strategy yielded 21 results from all databases and cross-referencing. Of these, all except for one (case-control) were cross-sectional and cohort studies. The pooled analysis found a significant association between adolescent pregnancy and depression (RR 1.34; 95% CI 1.05, 1.72, 6 studies, heterogeneity: Chi2 P 0.01; I2 = 60%); however, no association was found in anxiety (RR 1.05; 95% CI 0.26, 4.14, 2 studies; heterogeneity: Chi² P = 0.0003; I2 = 93%) and suicidal ideation (RR 3.21; 95% CI 0.17, 59.33; 3 studies; heterogeneity: Chi2 P < 0.00001; I2 = 98%).ImplicationThese findings suggest that the mental health needs of adolescent mothers must be addressed and innovative and effective interventions that support and address the mental health needs of adolescent mothers are needed to improve their mental health.