Memantine is an NMDA receptor antagonist that treats moderate to severe Alzheimer's disease dementia by blocking excessive glutamate activity, preventing excitotoxicity and neuronal damage in the brain. It functions as a low-affinity, uncompetitive open-channel blocker, entering NMDA receptors during activation to reduce pathological overstimulation while preserving normal synaptic transmission essential for memory and learning. Primarily indicated for Alzheimer's, it improves cognitive symptoms like attention and daily functioning, often combined with cholinesterase inhibitors, and shows investigational promise in conditions like schizophrenia, PTSD, and neuropathic pain due to glutamatergic modulation. Available orally under brands like Namenda, it offers symptomatic relief without altering disease progression.