Donepezil, marketed under the trade name Aricept® (Eisai), is a centrally acting reversible acetyl cholinesterase inhibitor. Its main therapeutic use is in the treatment of Alzheimer's disease where it is used to increase cortical acetylcholine. It is well absorbed in the gut with an oral bioavailability of 100% and easily crosses the blood-brain barrier. Because it has a half life of about 70 hours, it can be taken once a day. Initial dose is 5 mg per day, which can be increased to 10 mg per day after an adjustment period of at least 4 weeks.

Currently, there is no definitive proof that use of donepezil or other similar agents alters the course or progression of Alzheimer's disease. However, 6-12 month controlled studies have shown modest benefits in cognition and/or behavior. Pilot studies have reported that donepezil therapy may potentially have effects on markers of disease progression, such as hippocampal volume. Therefore, many neurologists, psychiatrists, and primary care physicians use donepezil in patients with Alzheimer's disease. In 2005, the UK National Institute for Clinical Excellence (NICE) withdrew its recommendation for use of the drug for mild-to-moderate AD, on the basis that there is no significant improvement in functional outcome; of quality of life or of behavioral symptoms. However, NICE revised its guidelines to suggest that donepezil be used in moderate stage patients for whom the evidence is strongest. While the drug is currently indicated for mild to moderate Alzheimer's, there is also evidence from 2 trials that it may be effective for moderate to severe disease. An example of this is a Karolinska Institute paper published in The Lancet in early 2006, which states that donepezil improves cognitive function even in patients with severe Alzheimer's disease symptoms.

Donepezil is sometimes used in combination with Memantine, a newer agent for Alzheimer's disease, as the response to both together is considered superior to donepzil alone. In moderate to severe Alzheimer's, a controlled clinical trial has shown that the addition of Memantine to stable donepezil therapy improves cognition, functioning and behavior.