Abstract
<jats:p>Background Child marriage/cohabitation before 18 years of age disproportionately affects girls worldwide, but its impacts on mental health are poorly understood. Existing research is mostly cross-sectional, hence unable to estimate causal impacts or longer-term outcomes of child marriage. Methods We analysed longitudinal cohort data across Ethiopia, India, Peru, and Vietnam from Young Lives to investigate the relationship between child marriage/cohabitation and life satisfaction and emotional symptoms. We used linear regression, difference-in-differences estimation (DiD), and propensity score matching (PSM) to examine short and longer-term impacts from age 19 to 29. Findings Across countries 5% (Peru) to 20% (India) of girls were child brides. Child marriage/cohabitation predicted lower life satisfaction -- pooled estimates at age 19 (-0.25 [95%CI=0.40,-0.10]), across 19-29 (-0.22 [95%CI=-0.32,-0.13]), and heterogeneity estimates suggest consistently negative impacts across countries. However, child brides have lower life satisfaction at age 8 even before marriage occurs, likely due to pre-existing disadvantages such as poverty that increase child marriage likelihood. DiD and PSM analyses confirm that most of the differences are due to pre-existing vulnerability and there is a small additional impact of child marriage on worse life satisfaction at age 19 (pooled matched estimate -0.09 [95%CI=-0.19, 0.00]). No differences in emotional symptoms were observed, nor any differences by age of marriage within the child-married sample. Interpretation Child brides have lower life satisfaction from childhood through to early adulthood, which is mostly explained by prior disadvantages and risk factors, with a small additional impact of child marriage itself.</jats:p>