Donepezil is used in the treatment of Alzheimer's disease and dementia in Parkinson's disease.
It should be used in patients with moderate to severe Alzheimer's disease.

Memory loss in Alzheimer’s disease is due to disturbance of message signals in the brain. Donepezil works by increasing the levels of acetylcholine, a chemical messenger involved in the transmission of nerve signals.

Nausea, Vomiting, Loss of appetite, Fatigue, Insomnia (difficulty in sleeping), Diarrhoea, Muscle cramp

• Do not take donepezil hydrochloride, if you are allergic to donepezil hydrochloride or any of the other ingredients of this medicine. 
• Avoid using donepezil hydrochloride, if you are breastfeeding.
• Doctor’s advice should be considered in case of patients with following history of disease conditions: stomach or duodenal ulcers; seizures (fits) or convulsions; heart condition (irregular or very slow heart beat); asthma or other long term lung disease; liver problems or hepatitis; urine or mild kidney disease.
• Do not use donepezil hydrochloride, if you are pregnant. 
• Donepezil hydrochloride is not intended for use in children and adolescents younger than 18 years.
• Donepezil hydrochloride should not be taken with alcohol because alcohol may change its effect.
• Do not drive or operate machinery.

Ques. Q. What is donepezil hydrochloride/ what is donepezil hydrochloride used for/ what does donepezil hydrochloride do?
Donepezil hydrochloride belongs to a group of medicines called acetylcholinesterase inhibitors and is used to treat the symptoms of dementia (which includes increasing memory loss, confusion and behavioral changes) in people diagnosed as having mild and moderately severe Alzheimer's disease

Ques. Q. Does Donepezil Hcl work?
Donepezil hydrochloride does work, but its effectiveness can be different based on individual response.