Memantine is a medication used for moderate to severe Alzheimer’s disease that works by blocking excessive stimulation of NMDA receptors in the brain, which can help protect nerve cells from damage. It helps with memory, thinking, and daily functioning, often prescribed alone or together with cholinesterase inhibitors like donepezil. Clinical benefits are modest but can make a difference in maintaining independence longer. Common side effects include dizziness, headache, constipation, and confusion, though it is usually well tolerated. While not a cure, memantine is an important option for managing symptoms in later stages of Alzheimer’s.