This information is for people who have dementia, or their carers. It tells you about donepezil (Aricept), a treatment used for dementia. It is based on the best and most up-to-date research.
Does it work?
Yes. If someone with mild or moderate Alzheimer's takes donepezil, their memory may improve and they may be able to think more clearly. But people who are helped by donepezil get only a little better.
Donepezil may also help people with vascular dementia.
There haven't been any studies of how donepezil affects people with Lewy body dementia.
What is it?
Donepezil is a tablet that you normally take at night. Its brand name is Aricept.
This medicine is for people with mild or moderate Alzheimer's disease.  To learn more, see How is Alzheimer's disease treated?
Guidance for doctors in the NHS says there may be some situations where other people with dementia can also be prescribed this drug. 
People with Alzheimer's disease and other dementias may have to take donepezil for up to four months before they get any benefit. If a person seems to be handling the drug well with no side effects after about a month, doctors may recommend a larger dose. The larger dose may work better.
How can it help?
People with mild or moderate Alzheimer's disease do better in tests of memory and thinking when they take donepezil.   But the improvement is usually small.
Donepezil may also help people with moderate or severe Alzheimer's disease to think more clearly, behave more normally, and do more daily activities, such as washing and dressing.   But not all research shows this.
Donepezil may help memory and thinking in people with vascular dementia. But again, the improvement is only small.  
One summary of all the research into donepezil and similar drugs said that the improvements might be so small that they made little difference to the person taking the drug. 
One large summary of the evidence found that donepezil seemed to work about as well as a similar drug called galantamine.  But another study found that donepezil might work slightly better. 
How does it work?
Donepezil is one of a group of drugs called cholinesterase inhibitors. Drugs in this group increase the amount of a chemical called acetylcholine in the brain. Acetylcholine is a chemical messenger ( neurotransmitter) in the parts of the brain that control memory, thinking, and decision making. People with dementia have less acetylcholine than other people. This may explain why they get confused and become forgetful.
When brain cells need to communicate with other brain cells, messages are carried by acetylcholine and other neurotransmitters. When the message has been delivered, the acetylcholine is destroyed by enzymes. Donepezil stops these enzymes working. So, the acetylcholine isn't destroyed and keeps helping signals travel through the brain. This might improve memory and thinking.