Inclusion Criteria:

          -  Male > 18 years of age

          -  Biopsy confirmed adenocarcinoma of the prostate

          -  Able to swallow and retain oral medication

          -  Hemoglobin A1C <7.0%

          -  Able and willing to participate in the full 12 months of the study

          -  Able to understand instructions related to study procedures

          -  Able to read and write English

        Exclusion Criteria:

          -  Metastatic Prostate Cancer

          -  Prostate Specific Antigen Doubling Time < 6 months

          -  Prior Chemotherapy, hormonal therapy, oral glucocorticoid therapy,
             Gonadotropin-releasing hormone analogue therapy

          -  Current or previous use of 5α-reductase inhibitors, antiandrogen drugs, metformin,
             oral or injectable diabetes drug

          -  Diagnosis of Type 1 Diabetes Mellitus

          -  Known hypersensitivity to metformin

          -  any condition associated with increased risk of metformin associated lactic acidosis

          -  participation in any investigational or marketed drug trial within 30 days prior to
             screening or during study period

          -  any unstable, serious co-existing medical conditions including but not limited to
             myocardial infarction, coronary bypass surgery, unstable angina, cardiac arrhythmias,
             clinically evident congestive heart failure, or cerebrovascular accident within 6
             months prior to screening

          -  history of megaloblastic anemia

          -  abnormal liver function test (total bilirubin, aspartate aminotransferase, alanine
             aminotransferase, alkaline phosphatase or serum creatinine above upper limit of
             normal)

          -  history of other malignancies, with the exception of adequately treated non-melanoma
             skin cancer, stage 1 melanoma, non-muscle invasive bladder cancer, or other solid
             tumors curatively treated with no evidence of disease for at least 5 years

          -  history or current evidence of substance abuse within 12 months of screening

          -  history of any illness (including psychiatric) that, in the opinion of the
             investigator, might confound the results of the study or post an additional risk to
             the subject