Inclusion Criteria:

* Age ≥ 18 years
* Diagnosis of brain tumor requiring cranial radiation treatment NOTE: Patient may be enrolled during or up to 3 years after completion of cranial radiation administered for treatment of primary or metastatic intracranial tumor
* Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2, AND Karnofsky performance status (KPS) of ≥ 70
* Expected survival ≥ 6 months in the opinion of treatment team
* Willing and able to adhere with the protocol for the duration of the study including undergoing treatment, and attending scheduled visits, and examinations
* The following laboratory values obtained ≤ 30 days prior to registration:

* Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 3 x ULN \[≤ 5 x upper limit normal (ULN) for patients with baseline liver disease\]
* Negative pregnancy test ≤ 8 days prior to registration for persons of childbearing potential only
* Ability to complete cognitive assessments and questionnaires by themselves or with assistance

Exclusion Criteria:

* Uncontrolled and/or intercurrent illness or other condition which limits safety of or compliance with study proceedings
* Pregnant or nursing, imprisoned, or lacking capacity for understanding
* Unable to swallow tablets or at risk for impaired absorption of oral medication
* Currently taking the study agent (i.e., metformin), and cannot safely discontinue if randomized to the control group (Group B)
* Known hypersensitivity or allergy to metformin
* Current use of resveratrol, CoQ10 (coenzyme Q10), coconut oil/other medium chain triglyceride-containing (e.g., Axona) supplements, or curcumin and unwilling to discontinue prior to registration and remain off these agents for study duration
* Unable to read and speak English. Note: English doses not to need to be primary language

Note: Other protocol defined Inclusion/Exclusion Criteria may apply.

Eligibility last updated 9/5/2024. Questions regarding updates should be directed to the study team contact.