Donepezil, marketed under the trade name Aricept by its developer Eisai

Eisai Co.

is a Japanese pharmaceutical company, ranking among the top 25 in the world by revenue and achieving $8 billion USD in sales for the fiscal 2008 year. Headquartered in Tokyo, Japan, it has some 10,000 employees, among them about 1,500 in research. Eisai is a member of the Topix 100 and Nikkei 225...

 and partner Pfizer

Pfizer

Pfizer, Inc. is an American multinational pharmaceutical corporation. The company is based in New York City, New York with its research headquarters in Groton, Connecticut, United States...

, is a centrally acting reversible acetylcholinesterase inhibitor

Acetylcholinesterase inhibitor

An acetylcholinesterase inhibitor or anti-cholinesterase is a chemical that inhibits the cholinesterase enzyme from breaking down acetylcholine, increasing both the level and duration of action of the neurotransmitter acetylcholine.- Uses :Acetylcholinesterase inhibitors:* Occur naturally as...

. Its main therapeutic use is in the palliative treatment of mild to moderate Alzheimer's disease

Alzheimer's disease

Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...

. Common side effects include gastrointestinal upset. It has an oral bioavailability of 100% and easily crosses the blood-brain barrier

Blood-brain barrier

The blood–brain barrier is a separation of circulating blood and the brain extracellular fluid in the central nervous system . It occurs along all capillaries and consists of tight junctions around the capillaries that do not exist in normal circulation. Endothelial cells restrict the diffusion...

. Because it has a half-life

Half-life

Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...

 of about 70 hours, it can be taken once a day.
Currently, there is no definitive proof that use of donepezil or other similar agents alters the course or progression of Alzheimer's disease.