Background <p>Substance use disorders (SUDs) pose notable public health challenge worldwide, with disparities often observed across demographic groups. However, there is limited evidence on the prevalence and sex-based inequalities of SUDs in Sierra Leone. This study aimed to analyze the prevalence of SUDs in Sierra Leone from 2000 to 2019, with a focus on sex-disaggregated trends and inequalities using data from the World Health Organization (WHO) equity data repository.</p> Methods <p>This cross-sectional study used age-standardized prevalence estimates of substance use disorders per 100,000 population from the WHO equity data repository accessed via the Health Equity Assessment Toolkit (HEAT). The WHO repository compiles and harmonizes data from multiple sources (e.g., national surveys, censuses, administrative records) and produces standardized, model-based estimates aligned with ICD-10 diagnostic categories. The study extracted sex-disaggregated estimates for Sierra Leone from 2000 to 2019, along with inequality measures (absolute difference, prevalence ratio, population attributable fraction, population attributable risk) that are pre-computed within HEAT. It conducted no independent statistical computations outside HEAT; my role involved defining the analytic scope, extracting, verifying, and interpreting HEAT outputs.</p> Results <p>The prevalence of SUDs in Sierra Leone remained relatively stable from 2000 to 2015, fluctuating between 821.6 and 824.5 per 100,000 population. However, a notable increase was observed between 2015 and 2019, with the prevalence rising to 845.1 per 100,000 population in 2019. Across all years, males consistently exhibited higher prevalence rates compared to females. In 2019, the prevalence among males was 975.6 per 100,000 (95% CI: 844.2–1112.6), while the prevalence among females was 718.3 per 100,000 (95% CI: 612.9–848.5). The absolute difference (D) in prevalence between males and females ranged from − 234.7 in 2005 to -257.3 in 2019, and the prevalence ratio (R) remained stable at approximately 0.7, indicating that males were 1.3 to 1.4 times more likely to experience SUDs than females. Despite this persistent disparity, the population attributable fraction (PAF) and population attributable risk (PAR) were consistently recorded as 0.0, suggesting that sex-based differences did not significantly impact the overall burden of SUDs in the population.</p> Conclusions <p>The findings show a consistent sex-based disparity in the prevalence of SUDs in Sierra Leone, with males bearing a significantly higher burden than females. While the overall prevalence remained stable over two decades, the recent increase underscores the need for targeted public health interventions to address the rising burden of SUDs. Policymakers should prioritize sex-specific strategies to mitigate these disparities and strengthen prevention and treatment programs. Future research should explore the underlying factors driving these trends and disparities to inform more effective policies and interventions.</p>