Metformin for the Prevention of Oral Cancer in Patients With Oral Leukoplakia or Erythroplakia

Inclusion Criteria: * Participants with oral leukoplakia or erythroplakia with mild, moderate, or severe histologic dysplasia or hyperplasia at the high risk sites (e.g., floor of mouth, tongue). Lesions arising from the radiation field are excluded as study lesions. * Measurable disease - minimum lesion size of 8x3 mm before initial biopsy * Age \>= 21 years. Adults 18-20 are not included as Canadian law prohibits purchase of cigarettes under the age of 21; investigators wish to keep criteria consistent among all trial sites. Also, smokers aged \< 20 years would most likely not have oral leukoplakia * Current and former smokers (\>= 5 packs in the lifetime) * Karnofsky performance scale \>= 70% * Leukocytes \>= 3,000/microliter * Absolute neutrophil count \>= 1,000/microliter * Platelets \>= 100,000/microliter * Total bilirubin =\< 1.5 x institutional upper limit of normal (ULN) * Aspartate aminotransferase (AST) (serum glutamic-oxaloacetic transaminase \[SGOT\]) and alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase \[SGPT\]) =\< 1.5 x institutional ULN * Estimation glomerular filtration rate (eGFR) \> 45 mL/min (eGFR calculated using the equation Chronic Kidney Disease Epidemiology Collaboration \[CKD-EPI\] creatinine) * Willing to use adequate contraception (barrier method, abstinence, subject or partner has had a vasectomy or partner is using effective birth control or is postmenopausal) for the duration of study participation because the effects of m…