Trial of Metformin for Colorectal Cancer Risk Reduction for History of Colorectal Adenomas and Elevated BMI

Inclusion Criteria: * History of prior colorectal adenomas within the past 3 years; only patients who have had adenomas endoscopically removed are eligible; documentation of colorectal adenomas must be determined via review of pathology reports * Body mass index (BMI) \>= 30; rounded to the nearest whole integer * Eastern Cooperative Oncology Group (ECOG) performance status 0-1 * Leukocytes ≥ 3,000/μL (\>= 2,500/μL for African-American participants) * Absolute neutrophil count \>= 1,500/μL (\>= 1,000/μL for African-American participants) * Platelets \>= 100,000/μL * Total bilirubin within normal institutional limits * Aspartate aminotransferase (AST) (serum glutamic oxaloacetic transaminase \[SGOT\])/alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase \[SGPT\]) =\< 1.5 X institutional upper limit of normal (ULN) * Creatinine within normal institutional limits * Women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation * A serum pregnancy test must be performed and be negative in all women of childbearing potential within 2 weeks prior to starting treatment * Ability to understand and willingness to sign a written informed consent document Exclusion Criteria: * History of colorectal cancer or other cancer(s) (except for non-melanoma skin cancers) within the last 3 years * Family history of hereditary intestinal polyp disorder (e.g., familial adenomatous polyposis \[FAP\], hereditary non-polyposis colorectal cancer \[HNPCC\], Putz-Jegher's disease) * Participants with diabetes * History of vitamin B12 deficiency or megaloblastic anemia * History of lactic acidosis * Diet or other medications for weight loss * Diseases associated with weight loss: anorexia, bulimia, or nausea * Treatment with medications that may increase metformin levels: cationic drugs, e.g., digoxin, amiloride, procainamide, trimethoprim, vancomycin, triamterene, and morphine * Treatment with other oral hypoglycemic agents * Participants who have undergone full bowel resection, ablation or other local therapies * Participants may not be receiving any other investigational agents * History of allergic reactions attributed to compounds of similar chemical or biologic composition to metformin * Participants with human immunodeficiency virus (HIV), cirrhosis of any cause, NASH (nonalcoholic steatohepatitis), or hepatitis (auto-immune or infectious) * Kidney disease or renal insufficiency (defined as serum creatinine \> 1.4 mg/dL for females or \> 1.5 mg/dL for males) * Metabolic acidosis, acute or chronic, including ketoacidosis * Uncontrolled intercurrent illness including, but not limited to: * Ongoing or active infection * Symptomatic congestive heart failure * Unstable angina pectoris * Cardiac arrhythmia * Psychiatric illness/social situations that would limit compliance with study requirements * Renal failure * Hepatic failure * Sepsis * Hypoxia * Pregnant or breastfeeding women are excluded * Participants anticipating elective surgery during the study period * Contraindication to colonoscopy/flexible sigmoidoscopy * Participants may not be using metformin, cimetidine (Tagament) furosemide (Lasix), nifedipine (Cardizem), Ranitidine (Zinetac or Zantac), digoxin (Lanoxin), Quinidine or any other drug contraindicated for use with metformin * Chronic alcohol use or a history of alcohol abuse * Participants with any medical psychosocial condition that, in the opinion of the investigator, could jeopardize participation in and compliance with the study criteria * Participants that regularly use aspirin (ASA), nonsteroidal anti-inflammatory drugs (NSAIDs), calcium, and cyclooxygenase (Cox)-2 inhibitors are not eligible for enrollment; however, patients that use aspirin 81 mg daily, or aspirin 325 mg, NSAIDs, calcium, or Cox-2 inhibitors at a frequency \< 10 times per month are eligible