Various CYP2C19-mediated metabolizer groups may arise as a result of inter-individual variability, which potentially influences the efficacy and safety of escitalopram. Hence, it is crucial to establish a comprehensive collection of information relevant to each phenotype regarding the efficacy and tolerability of therapy. This will enable psychiatrists to make optimal decisions for individual patients. The aim of the study: The aim of this study is to classify MDD patients into various CYP2C19 metabolizer groups and to determine the association between phenotype and treatment outcome. Materials and Methods: The study enrolled 119 escitalopram monotherapy-treated MDD patients aged 18–58. MADRS, HDRS-17, and CGI were used to measure efficacy at baseline, weeks 4, 8, and 12. Safety and tolerability outcomes were examined from occurring ADRs. Clinical outcomes were compared among phenotypes based on changes in HDRS-17 and CGI scores from week 4 to week 12. Results: Subjects were categorized by CYP2C19 genotype: 20 poor (PM), 64 intermediate (IM), 24 extensive (EM), and 11 ultra-rapid (UM) metabolizers. Response and remission occurred in 67.2 % and 26.8 % of the 119 subjects at the end of the 12th week of the study. The response rate in PM was much lower (21.6 %) compared to EM. There were 312 adverse drug reactions (ADRs), and 88 (73.94 %) individuals had at least one. In safety data, nervousness was the most common ADR among the four groups 66 (55.4 %), followed by decreased appetite 48 (40.3 %). There were no severe ADRs. Men had more ADRs than women. Conclusion: CYP2C19 genotyping may help personalize escitalopram medication. The study found that the reduced ability of PM to metabolize escitalopram is probably associated with the decreased efficacy and tolerance shown in PM compared to EM and IM. The relationship between metabolizer status and treatment response followed the anticipated direction. Our findings should guide future clinical studies that include pharmacokinetic assessments