Like all medicines, donepezil can cause side effects in some people, but many people have no side effects or only minor ones.
Common side effects
These common side effects of donepezil happen to more than 1 in 100 people. There are things you can do to help cope with them:
Diarrhoea
Drink lots of fluids, such as water or squash, to avoid dehydration. Signs of dehydration include peeing less than usual or having dark strong-smelling pee.
Do not take any other medicines to treat diarrhoea, including rehydration salts, without first speaking to a pharmacist or doctor.
If you take the combined contraceptive pill or progestogen-only pill and you have severe diarrhoea for more than 24 hours, your contraception may not protect you from pregnancy. Check the pill packet for advice.
Feeling sick (nausea)
Try to stick to simple meals and try not to eat very rich, fatty or spicy food. You could also try taking regular sips of water.
Headache
Make sure you rest and drink plenty of fluids. If it's bothering you, ask a pharmacist to recommend a painkiller.
Talk to a doctor if your headaches last longer than a week or are severe.
Feeling sleepy in the daytime or feeling dizzy
Try taking your medicine at night. If you feel dizzy or tired do not drive or ride a bike until you feel better, and fully alert.
Side effects are less likely to happen if your doctor starts you on the lower 5mg dose for at least a month.
As your body gets used to donepezil, these side effects should wear off. If the advice on how to cope does not help and you're bothered by them, speak to a doctor. They may want to adjust your dose or recommend a different medicine.
Serious side effects
Less than 1 in 100 people have serious side effects with donepezil.
Call a doctor or call 111 now if you, or the person you're caring for, have:
- yellowing skin (this may be less obvious on black or brown skin) or the whites of your eyes turn yellow, or if you have pale poo and dark pee – these can be signs of liver problems
- severe indigestion, heartburn or stomach pain, severe or continued vomiting – these can be signs of an ulcer in your stomach or gut
- black poo, or blood or something that looks like coffee grounds in your vomit – these can be signs of internal bleeding
- muscle weakness or cramps and pains in your muscles (that you did not have before) – these can sometimes be signs of muscle and kidney problems
- a high temperature together with stiff muscles, sweating, confusion and seeing or hearing things that are not there – these can be signs of a rare side effect called neuroleptic malignant syndrome
Urgent advice: Call 999 and ask for an ambulance if:
- you, or the person you're caring for, have had a seizure or fit
Serious allergic reaction
In rare cases, donepezil may cause a serious allergic reaction (anaphylaxis).
Immediate action required: Call 999 now if:
- your lips, mouth, throat or tongue suddenly become swollen
- you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
- your throat feels tight or you're struggling to swallow
- your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
- you suddenly become very confused, drowsy or dizzy
- someone faints and cannot be woken up
- a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)
You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.
These can be signs of a serious allergic reaction and may need immediate treatment in hospital.
Other side effects
These are not all the side effects of donepezil. For a full list see the leaflet inside your medicines packet.
You can report any suspected side effect using the Yellow Card safety scheme.