The goal of this clinical trial is to test whether the gamma - glutamylcystiene (GGC) oral supplement can reach the brain and subsequently increase antioxidant glutathione (GSH) level in people with repetitive head impact (RHI). This will reduce the oxidative stress related injury in people with RHI.This unique study's main objective is to test the:

1. Change in GSH in brain and blood levels through GGC supplementation.
2. Change in the cognitive function in RHI patients due to GGC supplementation.

This study is designed to evaluate the effects of GGC supplementation in patients with a history of repetitive head impacts (RHI) who are at risk for developing Traumatic Encephalopathy Syndrome (TES). The trial will include specific individuals who satisfy the eligibility criteria.

Inclusion Criteria:

• Retired NFL player, retired Navy SEAL/army personnel with combat experience exposed to repetitive head impact;
• Memory and behavioral complaint per self- or informant-report;
• Age (30 to 70 years of age) years;
• Able to read and write in English and to give consent to participate in the study.

Exclusion Criteria:

• Presence of pacemakers, aneurysm clips, artificial heart valves, ear implants, metal fragments in the eyes, skin, or body.
• Subjects with claustrophobia.
• Subject with mild cognitive impairment [TICS score of 29 or lower OR >=1.0 standard deviations below age-expectation on at least two cognitive members within the same cognitive domain (e.g. memory, attention, etc.) on the baseline neuropsychological testing;
• Subjects with a history of cancer;
• Subjects with active psychosis or delirium;
• Subjects with chronic kidney (creatinine > 1.5mg/dL) or liver disease (AST ≥ 1.5 ULN; ALT ≥1.5 ULN) within 30 days prior to enrollment;
• Subjects on antioxidant therapy (gingko biloba or N-acetylcysteine) or illicit drug abuse/dependence (cocaine, heroin, marijuana, or fentanyl;
• Repeated head injury patients with neurosurgical intervention and;
• Subjects with repeated head injury within the last 90 days.](streamdown:incomplete-link)

Clinical study report data will be provided after the study data is analyzed and published. A comprehensive report will be sent to the IRB. The respective agency will be reported accordingly. Requests for the release of data must be submitted in writing to the PI, clearly stating the purpose of the request, the specific data needed, and the intended use. The PI, in collaboration with the research team, will review each request to ensure compliance with institutional policies, ethical standards, and any relevant data use agreements.