Donepezil is a prescription-only drug used to alleviate some of the symptoms of Alzheimer'splugin-autotooltip__plain plugin-autotooltip_bigAlzheimer's disease
"Alzheimer’s disease is a chronic progressive neuro-degenerative disorder characterised by three primary groups of symptoms. The first group (cognitive dysfunction) includes memory loss, language difficulties, and executive dysfunction (that is, loss of higher level planning and intellectual coordination skills). The second group comprises psychiatric symptoms and behavioural disturbances — for example, depression, hallucinations, delusions, agitation — collectively termed … disease. There are currently around 5 million prescriptions per year in the US alone. It's sold under the brand names of Aricept, Namzaric and others.
The drug is a centrally-acting inhibitor of enzymes which reduce the levels of naturally occurring acetylcholine, thus increasing its availability - but the 'mechanism of action' with regard to Alzheimer's is currently unknown.
See: Wikipedia