Metformin is one of the most prescribed medications in the United States, mainly due to its utility in treating patients with diabetes. Continued research into metformin’s mechanisms have yielded interesting findings on its cancer suppressing abilities, including its actions in prostate cancer. With these mechanisms in mind, we sought to investigate the potential effects of metformin use on PSA levels in patients with prostate cancer. Using the TriNetX research network, we collected data forming two cohorts of patients with diabetes and same-stage prostate cancer, with and without metformin treatment, cohort A and cohort B respectively. We found a difference between PSA and metformin usage. The mean serum PSA level among patients with the diagnosis of prostate cancer and metformin use in Cohort A (N=45,145) was 20.1 ± 17.8 and the mean serum PSA level for patients with the diagnosis of prostate cancer and no metformin use (N=440,464) was 34.3 ± 31, p<0.0002. We identified a significant decrease in the mean PSA level in metformin users compared to non-metformin users. Further investigation on the effects of metformin on PSA levels is needed to clarify metformin-induced dampening of PSA in screening for prostate cancer diagnosis.