Memantine Targeting Neurovascular Dysfunction After Mild and Moderate Traumatic Brain Injury (MEND)

The goal of this pilot clinical trial is to learn whether memantine can be given safely and successfully to adults in hospital with a mild or moderate traumatic brain injury (TBI). Memantine is approved to treat Alzheimer's disease, but it is not approved to treat TBI. The study will also test whether brain scans and other assessments are suitable for a larger trial. TBI can damage the blood-brain barrier. This protective lining controls what can pass from the bloodstream into the brain. Researchers can measure this damage with a specialized magnetic resonance imaging (MRI) scan using contrast dye. The main questions are: * Can participants start memantine soon after their injury and take it for three months? * How safe and tolerable are daily memantine doses of 20 mg and 30 mg? * Can MRI scans measure changes in the blood-brain barrier from the start of the study to three months? * Can researchers complete the study visits and collect enough information to plan a larger trial? The study will include 45 adults admitted to the Halifax Infirmary in Nova Scotia, Canada, with a non-penetrating mild or moderate TBI. A computer will assign each participant by chance to one of three groups. One group will receive 20 mg of memantine per day. Another group will receive 30 mg per day. The third group will receive usual care without memantine. The memantine dose will increase gradually based on how well each participant tolerates it. Participants will: * Receive usual care, with or without memantine for three months; * Have specialized MRI scans near the start of the study and at three months; * Have recordings of brain activity near the start, at three months, and at six months; and * Complete tests and questionnaires about symptoms, memory, attention, mood, daily function, disability, and quality of life. Researchers will compare the groups to look for differences in blood-brain barrier changes, side effects, and recovery measures. Because this is a small pilot study, it is not designed to prove that memantine improves recovery. Its results will instead help researchers choose a dose, assess safety of drug delivery, and design a larger trial.