Donepezil: dementia medicine uses and side effects

Donepezil is used to help with some types of dementia. The NHS names Alzheimer's disease, Parkinson's disease, dementia with Lewy bodies and mixed dementia. It can help with symptoms such as forgetfulness and confusion, but it is not a cure for dementia and it does not stop the underlying condition.

It is prescription-only. Aricept and Aricept Evess are the UK brands listed by the NHS. The NHS page does not describe the mechanism, so this guide sticks to what it says about use.

Donepezil is available as tablets, tablets that melt in the mouth, and a liquid. Standard tablets are swallowed with water; the melt-in-the-mouth tablets dissolve on the tongue without liquid; the liquid is measured only with the spoon provided and not a kitchen teaspoon.

The NHS says the usual starting dose is 5mg once a day, and the dose may increase to 10mg after one month. Tablets come in 5mg and 10mg strengths and the liquid in 5mg/5ml. The specialist who prescribes it makes the final decision for each person.

It can be taken with or without food. The NHS says it is best taken at bedtime because of possible dizziness, although taking it in the morning is acceptable if it disturbs sleep or causes vivid dreams.

Expect patience. The NHS says it usually takes at least a month for donepezil to start working, and for some people longer. Carers sometimes judge benefit by small things, such as an easier conversation or a steadier routine, so notes kept for review appointments can help.

Common effects, in more than 1 in 100 people, are diarrhoea, nausea, headache and daytime sleepiness or dizziness. For diarrhoea, drink plenty of fluids; severe diarrhoea lasting more than 24 hours may affect the contraceptive pill. For nausea, bland food and small sips of water help. If headaches persist beyond a week or are severe, speak to a doctor. Effects usually ease as the body adjusts.

Less common serious effects include signs of liver problems (yellow skin or eyes, pale stools, dark urine), ulcers (severe indigestion or stomach pain, persistent vomiting), bleeding (black stools or blood in vomit), muscle weakness or cramps, and neuroleptic malignant syndrome (high fever with stiff muscles, sweating, confusion). The NHS says to call 111 or a doctor for these. Seizures and signs of anaphylaxis need a 999 call.

Most adults aged 18 and over can take donepezil. The NHS asks people to tell their doctor beforehand if they have had an allergic reaction to it, or have any of the following.

• Liver problems.

• A history of stomach, gut or intestinal ulcers.

• An irregular or slow heartbeat.

• Asthma or lung disease such as COPD.

• Previous seizures or fits.

• Difficulty passing urine.

Named interacting medicines on the NHS page include heart medicines (amiodarone, atenolol, bisoprolol, digoxin, verapamil), the epilepsy medicines phenytoin and carbamazepine, NSAIDs such as aspirin and ibuprofen, risperidone, olanzapine, fluoxetine, erythromycin and rifampicin, and general or local anaesthetics. Paracetamol is safe to combine.

St John's wort can lower donepezil levels in the blood and may reduce its effect. Alcohol both reduces how well donepezil works and increases side effects.

If you miss a dose, skip it and take the next one the following day. Never double up, and speak to a doctor if you have missed doses for more than a week.

Regular check-ups decide whether treatment continues. The NHS notes the effect may diminish after 6 to 12 months, but stopping may make symptoms worse, so discuss concerns with the doctor before changing anything. For overdose, use 111, and call 999 or go to A&E for dizziness, nausea, vomiting, drooling, a slow heart rate, breathing problems, fainting or seizures. Do not drive yourself.

The NHS says there is little information about donepezil and unborn babies, so it is not recommended during pregnancy, and it is not typically recommended while breastfeeding. There is no evidence it affects fertility in men or women. These points matter chiefly for younger-onset dementia and for people prescribed it for other reasons.