Impact of Metformin on Immuno-virologic Parameters in HIV

Inclusion Criteria: * HIV+ * On suppressive ART stable for \> 1 year * Plasma HIV RNA \< 50 copies/mL within 3 months of entry, with no HIV RNA \> 200 copies/mL within the past 6 months prior to entry * Age \>40 years * Ability and willingness to provide written informed consent Exclusion Criteria: * Uncontrolled chronic medical condition or cancer * Acute illness within 2 weeks of entry * Diagnosis of diabetes by history, fasting blood glucose \>126, or by HgbA1c \> 6.5 * Chronic, uncontrolled diarrhea * Known hypersensitivity or contraindication to metformin use * Current presence of hepatitis C including currently on or intent to start therapy for hepatitis C within the 48 week duration of study. * Serum B12 level below the reference normal range as listed by the commercial lab utilized for this study (Diagnostic Laboratory Services) * Pregnancy, or intent to become pregnant or nursing an infant * Any immunomodulator, HIV vaccine, any other vaccine, or investigational therapy within 30 days of study entry. * Current uncontrolled coronary artery disease or NYHA Class 3 or 4 congestive heart failure * History of liver cirrhosis * Current use of zidovudine, stavudine or didanosine * The following lab values * Hemoglobin \< 9.0 g/dL * Absolute neutrophil count \< 1000/μL * Platelet count \< 50,000/μL * AST (SGOT) and ALT (SGPT) \> 5x upper limit of normal (ULN) * Calculated creatinine clearance (Cockcroft and Gault) \< 50 ml/min * Active or recent past history (within past 2 years) of illicit substance or alcohol use or abuse which, in the judgment of the Investigator, will interfere with the patient's ability to comply with the protocol requirements * Patients, who, in the opinion of the Investigator, are unable to comply with the dosing schedule and protocol evaluation or for whom the study may not be advisable