Finasteride is the main therapy for benign prostatic hyperplasia (BPH) because it blocks 5-? reductase. It prevents testosterone from changing into dihydrotestosterone. This keeps the prostate from getting bigger and affects the way prostate-specific antigen (PSA) levels operate. These pharmaceutical activities confer therapeutic advantages; nonetheless, they may influence the interpretation of PSA findings in prostate cancer screening and the associated clinical decisions.         The goal of this systematic review was to bring together all the information that is out there regarding how finasteride affects total PSA, free PSA, prostate volume, and PSA density (PSAD), so that we could have a full picture of its therapeutic effects. We performed an exhaustive search of PubMed and ScienceDirect for studies examining the relationship between finasteride use and blood PSA levels (August 2025). The review utilized the PRISMA approach for systematic reviews and meta-analyses. Two reviewers used strict standards to determine whether participants were eligible for the analysis and data collection.Only nine of the initial 2,473 studies met all the inclusion criteria. The study found that finasteride always decreased total PSA levels by 30% to 50% and free PSA levels by as much as 45%. The prostate volume and PSAD both went down by around 5% to 20%. These comparable tendencies highlight how vital it is to apply adjustment factors when looking at the PSA levels of men who are taking finasteride for BPH.