Donepezil

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Donepezil is an acetylcholinesterase inhibitor licensed in the United Kingdom for the symptomatic treatment of mild to moderate Alzheimer's disease.

It is one of three cholinesterase inhibitors recommended by NICE (Technology Appraisal 217), alongside rivastigmine and galantamine, as first-line pharmacological options for Alzheimer's disease.

Donepezil was originally marketed as Aricept but is now widely available as a generic medicine.

It is taken as a single daily tablet (5 mg or 10 mg) and works by increasing the availability of acetylcholine in the brain, temporarily improving or stabilising cognitive function, daily activities, and behaviour.

Alzheimer's disease is the most common form of dementia, accounting for approximately 60 to 70% of all dementia cases in the UK.

An estimated 900,000 people in the UK are living with dementia, and this number is projected to rise to over 1.5 million by 2040 as the population ages.

The disease is characterised by progressive neurodegeneration, beginning with episodic memory loss and advancing to affect language, spatial orientation, judgement, and the ability to carry out daily activities.

While no cure currently exists, symptomatic treatments including donepezil can provide meaningful improvements in quality of life for patients and their families.

This page provides a comprehensive clinical overview of how donepezil works, who it is suitable for, dosing, side effects, monitoring requirements, NICE guidance, and how to access treatment in the UK.

Important safety information about donepezil

Before reading further, note the following essential safety points. Donepezil is a prescription-only medicine (POM) that should be initiated by a specialist experienced in dementia care.

• Donepezil does not cure or reverse Alzheimer's disease. It provides symptomatic benefit that may last for months to years.
• Treatment must be initiated by a specialist (psychiatrist, geriatrician, or neurologist) and should be continued only while it provides worthwhile benefit, assessed through regular clinical review.
• Donepezil can cause bradycardia (slow heart rate) and may interact with heart-rate-lowering medicines. An ECG may be required before starting treatment.
• Common side effects include diarrhoea, nausea, headache, and insomnia. These usually settle with time.
• Avoid concurrent use of anticholinergic medicines (such as oxybutynin, amitriptyline) as they counteract the benefit of donepezil.

Understanding Alzheimer's disease

Alzheimer's disease is a progressive neurodegenerative disorder characterised by the accumulation of amyloid-beta plaques and neurofibrillary tangles (composed of hyperphosphorylated tau protein) in the brain.

These pathological changes lead to synaptic loss, neuronal death, and brain atrophy, particularly in the hippocampus and cerebral cortex, regions critical for memory and higher cognitive function.

One of the earliest and most consistent neurochemical changes in Alzheimer's disease is the degeneration of cholinergic neurones in the nucleus basalis of Meynert, a structure in the basal forebrain that provides the major cholinergic input to the cerebral cortex.

The resulting deficit of acetylcholine correlates with the severity of cognitive impairment and forms the basis of the cholinergic hypothesis of Alzheimer's disease.

This hypothesis underpins the use of cholinesterase inhibitors, which aim to compensate for cholinergic loss by increasing the availability of acetylcholine at surviving synapses.

Alzheimer's disease progresses through recognisable stages.

In the early (mild) stage, the person may have difficulty remembering recent events, finding words, or managing finances, while retaining awareness and independence in most daily activities.

In the moderate stage, confusion increases, language difficulties become more apparent, personality and behaviour may change, and the person requires increasing assistance with daily tasks.

Donepezil is licensed for the mild to moderate stages of the disease.

How donepezil works: mechanism of action

Donepezil hydrochloride is a centrally acting, reversible, non-competitive inhibitor of acetylcholinesterase (AChE), the enzyme responsible for breaking down acetylcholine at the synaptic cleft.

By inhibiting AChE, donepezil increases the concentration of acetylcholine available to bind to muscarinic and nicotinic receptors on postsynaptic neurones.

This enhanced cholinergic transmission partially compensates for the loss of cholinergic neurones and can improve or stabilise cognitive function, activities of daily living, and behavioural symptoms.

Donepezil is highly selective for AChE over butyrylcholinesterase (BuChE), which is present in both the central nervous system and peripheral tissues.

This selectivity may contribute to a somewhat more favourable peripheral side-effect profile compared with agents that also inhibit BuChE (such as rivastigmine).

However, cholinergic side effects (gastrointestinal symptoms, bradycardia, muscle cramps) still occur because AChE is also present at the neuromuscular junction and in the autonomic nervous system.

Donepezil has a long plasma elimination half-life of approximately 70 hours, allowing convenient once-daily dosing. Steady-state plasma concentrations are achieved within approximately 15 days.

It is metabolised in the liver primarily by CYP2D6 and CYP3A4 and is excreted renally. No dose adjustment is required for renal impairment.

Clinical evidence and NICE guidance

Donepezil has been evaluated in multiple large randomised controlled trials.

The pivotal studies demonstrated statistically significant improvements in cognitive function (measured by the ADAS-Cog scale), global clinical impression (CIBIC-plus), and activities of daily living compared with placebo over 12 to 24 weeks.

The 10 mg dose provided additional modest benefit over 5 mg in some studies, though with more frequent side effects.

NICE Technology Appraisal 217 (updated 2018) recommends donepezil, rivastigmine, and galantamine as options for managing mild to moderate Alzheimer's disease.

The appraisal states that treatment should be initiated only by specialists experienced in dementia care but can be continued by GPs under shared care arrangements.

Treatment should be reviewed regularly (typically every 6 to 12 months) using standardised cognitive, functional, and behavioural assessments.

Donepezil should be continued only while it is judged to provide a worthwhile clinical benefit, taking into account the views of the patient (where possible) and their carer.

The NICE dementia guideline (NG97, 2018) provides broader management recommendations including non-pharmacological interventions (cognitive stimulation therapy, tailored activities, carer support), management of behavioural and psychological symptoms, and advance care planning. Donepezil sits within this comprehensive care framework.

Starting donepezil: who can take it

Donepezil is indicated for patients with a confirmed diagnosis of Alzheimer's disease of mild to moderate severity.

Diagnosis should be made by a specialist using established criteria (NICE recommends the DSM-5 or ICD criteria) and supported by cognitive testing and, where appropriate, neuroimaging.

There is no upper age limit for treatment. Patients with comorbidities can often take donepezil, but caution is needed in certain groups.

Patients with cardiac conduction disorders (sick sinus syndrome, atrioventricular block), active peptic ulcer disease, asthma, COPD, or a history of seizures require careful assessment before starting.

Patients already taking anticholinergic medicines should have these reviewed and rationalised before starting donepezil, as anticholinergics directly counteract its mechanism of action.

Dosage and administration

The starting dose is 5 mg once daily, taken in the evening before bedtime.

After at least 4 weeks at 5 mg, the dose may be increased to 10 mg once daily based on clinical response and tolerability.

Tablets should be swallowed whole with water.

Orodispersible tablets can be placed on the tongue, allowed to dissolve, and swallowed without water, which can be helpful for patients with swallowing difficulties.

Evening dosing is recommended to reduce the impact of cholinergic side effects (particularly nausea) on daytime function, and because peak plasma concentrations the following morning align with waking hours when cognitive demands are greatest.

Treatment should be continuous. If a dose is missed, skip it and take the next dose at the usual time.

If treatment is interrupted for more than a few days, consider restarting at 5 mg and re-titrating.

Regular clinical review should determine whether to continue, maintain the dose, or discontinue treatment.

Monitoring and review

NICE recommends formal review every 6 to 12 months by a specialist or under shared care with the GP.

Review should include standardised cognitive testing (such as the MMSE, ACE-III, or MoCA), assessment of functional abilities (how the person manages daily activities), evaluation of behavioural and psychological symptoms, physical health review (including weight, blood pressure, heart rate), carer perspective (carers often notice changes in behaviour and function that formal tests may not capture), and review of concurrent medications (particularly anticholinergics).

Treatment should be continued as long as it is judged to provide worthwhile benefit.

This does not necessarily mean measurable improvement on cognitive scores; stabilisation of function or behaviour in a progressive disease represents meaningful benefit.

Conversely, if there is clear evidence that donepezil is no longer effective or is causing unacceptable side effects, a trial discontinuation may be appropriate, with close monitoring for deterioration.

Side effects of donepezil

Common side effects

The most frequently reported side effects are gastrointestinal: diarrhoea (affecting approximately 10% of patients in trials), nausea (11%), and vomiting (5%).

Other common effects include headache, dizziness, insomnia, fatigue, muscle cramps, and loss of appetite. These are more common at the 10 mg dose and during dose titration.

They usually settle within the first few weeks. Taking donepezil in the evening and ensuring the patient eats a light meal beforehand can help.

Uncommon and rare side effects

Less common effects include abdominal pain, urinary incontinence, agitation, aggression, vivid dreams, and syncope (fainting).

Rare but clinically important effects include bradycardia and heart block, seizures, gastrointestinal haemorrhage, neuroleptic malignant syndrome (when antipsychotics are co-prescribed), rhabdomyolysis, and hepatitis.

Weight loss may occur over time and should be monitored, as it can contribute to frailty in elderly patients.

When to seek medical attention

Carers should seek urgent medical advice (call 999 or attend A&E) if the patient collapses, has a seizure, develops a very slow or irregular heartbeat, passes black tarry stools or vomits blood, or develops high fever with muscle rigidity.

Contact the GP or NHS 111 for persistent diarrhoea or vomiting, significant weight loss, worsening agitation or aggression, urinary incontinence, or new falls.

Report adverse reactions via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk .

Warnings and precautions

Cardiac effects

Cholinesterase inhibitors increase vagal tone and can cause bradycardia.

This is usually clinically insignificant in healthy individuals but can be dangerous in patients with sick sinus syndrome, atrioventricular block, or those taking concurrent rate-lowering medicines (beta-blockers, digoxin, diltiazem, verapamil).

An ECG before starting treatment is recommended for patients with known cardiac history or symptoms. Syncopal episodes should prompt urgent cardiac assessment.

Gastrointestinal risk

Increased gastric acid secretion from cholinergic stimulation raises the risk of peptic ulceration and gastrointestinal bleeding, particularly in patients with a history of peptic ulcer disease and those taking NSAIDs or anticoagulants.

Monitor for dark stools, abdominal pain, and weight loss.

Drug interactions

Anticholinergic medicines directly oppose the cholinergic action of donepezil and should be minimised or avoided.

Common culprits include oxybutynin (for overactive bladder), amitriptyline (for pain or mood), chlorphenamine (antihistamine), and certain antipsychotics. A medication review is essential before starting donepezil.

Potent CYP2D6 and CYP3A4 inhibitors (ketoconazole, fluoxetine, paroxetine, quinidine) may increase donepezil levels, while enzyme inducers (carbamazepine, phenytoin, rifampicin) may reduce them.

Anaesthesia

Donepezil can potentiate the effects of depolarising neuromuscular blocking agents (suxamethonium). Inform the anaesthetist before any surgical procedure.

Donepezil compared with other dementia medicines

Three cholinesterase inhibitors are available in the UK: donepezil, rivastigmine, and galantamine. All are recommended by NICE for mild to moderate Alzheimer's disease and have similar overall efficacy.

Donepezil's advantages include once-daily dosing, a long track record, and availability as an orodispersible tablet.

Rivastigmine is available as a transdermal patch, which may be preferred if oral administration is difficult.

Galantamine has a dual mechanism (cholinesterase inhibition plus nicotinic receptor modulation) but requires twice-daily dosing in its immediate-release form.

The choice between agents is usually based on individual tolerability, ease of administration, and patient preference.

Memantine, an NMDA receptor antagonist, is recommended by NICE as an option for moderate Alzheimer's disease in patients who cannot tolerate or have contraindications to cholinesterase inhibitors, or as add-on therapy to a cholinesterase inhibitor in moderate to severe disease.

How to access donepezil treatment in the UK

Donepezil should be initiated by a specialist experienced in dementia care.

The usual pathway begins with a GP referral to a memory assessment service, where the patient undergoes diagnostic evaluation including cognitive testing, blood tests, and often a brain scan (CT or MRI).

If Alzheimer's disease is diagnosed, the specialist can start donepezil.

Once the patient is established on a stable dose, prescribing is often transferred to the GP under a shared care agreement, with specialist review at regular intervals.

Donepezil is available on the NHS. Generic donepezil is the standard dispensed product and is cost-effective.

The standard NHS prescription charge in England is currently 9.90 pounds per item; prescriptions are free in Scotland, Wales, and Northern Ireland.

Patients aged 60 and over are exempt from prescription charges in England.

Supporting someone with Alzheimer's disease

Medication is one part of a comprehensive approach to dementia care. NICE recommends cognitive stimulation therapy (group-based structured sessions) for people with mild to moderate dementia.

Maintaining physical activity, social engagement, and meaningful daily activities supports overall wellbeing.

Carers should be offered assessment and support in their own right, including respite care, training, and access to peer support groups.

Organisations such as the Alzheimer's Society (alzheimers.org.uk) provide a national helpline, local support services, and information resources.

Advance care planning, including lasting power of attorney and preferred place of care discussions, should be introduced early while the person can participate in decisions.

When to seek further medical advice

Contact the GP or memory service if the patient's cognition or behaviour worsens noticeably, if side effects are troublesome, if the patient is losing weight or falling more frequently, or if the carer is struggling to cope.

Seek urgent care (call 999) for seizures, collapse, severe chest pain, or signs of gastrointestinal bleeding. NHS 111 can provide advice outside GP hours.

Sources

• Donepezil 5 mg/10 mg Film-Coated Tablets, Summary of Product Characteristics (EMC)
• Donepezil hydrochloride, British National Formulary (BNF)
• NICE TA217: Donepezil, galantamine, rivastigmine and memantine for Alzheimer's disease
• NICE NG97: Dementia, assessment, management and support
• Alzheimer's disease, NHS
• Alzheimer's Society
• MHRA Yellow Card Scheme