Aim To investigate treatment retention rates, dropout predictors and dropout chronology across patients with substance use disorders at a Women-Specific Outpatient Service in Brazil, across different age strata: Emerging Adults (18-25), Middle Aged Adults (26-59), and Older Adults ( 60+). Methods An observational cohort study, across 27 years. Sociodemographic and other exposures information were collected at enrollment. Survival curves with dropout as event were estimated for each age stratum and log rank tests were performed. Survival probabilities and Cox proportional hazards models were used to gauge dropout risk and determine dropout risk factors. Hazard functions of dropout were estimated to understand chronology of dropout across age strata. Results 714 women were included. Emerging adults exhibited significantly lower treatment retention with 10.2% survival at 104 weeks p<0.0001), and increased rate of early dropout, compared to the other age stratas. Higher education was a protective factor, associated with lower dropout risk (HR= 0.73, p=0.02). Cocaine/crack as the main substance of abuse was a risk factor (HR=1.36 , p=0.003). Hazard function curves showed a first peak of dropout in emerging adults at 12 weeks of treatment. Conclusions Emerging adulthood is a critical period for health interventions. The gender gap is narrowing and even inverting among Emerging Adults, and women are still underrepresented in studies. We found very high and early dropout rates among Emerging Adults in our sample. These findings underscore the necessity for early-stage risk stratification and intervention protocols for this subpopulation.