Donepezil is a medication primarily used to treat symptoms of Alzheimer's disease. It works by increasing levels of a neurotransmitter called acetylcholine in the brain, which helps improve memory and cognitive function in some patients. This drug is typically prescribed for mild to moderate cases of Alzheimer's and is taken orally, usually once a day. While it can help manage symptoms, it does not cure the disease or stop its progression. Common side effects may include nausea, diarrhea, and insomnia.