Donepezil

What it is

Donepezil is a piperidine-based reversible inhibitor of acetylcholinesterase, taken once a day as a tablet or orally disintegrating tablet (and in some countries as a weekly patch). The US label approves it for dementia of the Alzheimer's type at mild, moderate and severe stages. Its absorption is not changed by food, and it is metabolised by CYP2D6 and CYP3A4.

What the research says

Donepezil produces small, measurable improvements in cognition and day-to-day function in Alzheimer's dementia that do not change the course of the disease. A Cochrane review of 30 trials (8,257 people, most six months or shorter, 17 of them industry funded) found a 2.67-point advantage on the 70-point ADAS-Cog scale and a 1.05-point advantage on the MMSE at 26 weeks, with moderate-quality evidence - and no difference from placebo on behavioural symptoms or quality of life. Side effects are mostly cholinergic (nausea, diarrhoea, insomnia, muscle cramps) and more common than on placebo (72% vs 65%). An Ontario cohort of 19,803 people on cholinesterase inhibitors found higher rates of syncope, bradycardia, pacemaker insertion and hip fracture. For mild cognitive impairment, which is not an approved use, a Cochrane review concluded the drugs should not be recommended.

Evidence grade: Well established.

How it works

Drug class: Reversible acetylcholinesterase inhibitor (cholinesterase inhibitor), used as a symptomatic treatment for dementia

In Alzheimer's disease the brain loses cholinergic nerve signalling. Donepezil blocks acetylcholinesterase, the enzyme that breaks down acetylcholine, so more acetylcholine stays available at the synapse. The label is explicit that this is a compensation, not a cure: there is no evidence it changes the underlying disease. (Source 1)

What it is used for

• Small but consistent symptomatic benefit on cognition, activities of daily living and clinician-rated global state at 12 to 26 weeks; moderate-quality evidence. No effect on behavioural symptoms or quality of life, and no evidence that the underlying disease is altered. Evidence: established. (Source 2)
• A Cochrane review of nine trials in 5,149 people found essentially no effect on cognitive test scores and no strong evidence of an effect on progression to dementia, with significantly more adverse events. The authors say cholinesterase inhibitors should not be recommended for mild cognitive impairment. Evidence: not-supported. (Source 3)
• A Cochrane network meta-analysis of eight trials (4,373 people) found donepezil 5 mg improves cognition slightly with high-certainty evidence, and donepezil 10 mg probably more so, but says in both cases the size of the change is unlikely to be clinically important. Donepezil 10 mg caused slightly more adverse events than placebo. Evidence: limited. (Source 4)

Interactions

• Anticholinergic medicines (for example oxybutynin, some antihistamines, some tricyclics) (label): Donepezil raises acetylcholine; anticholinergics block it. Each works against the other, so taking both can cancel the intended effect of either. (Source 5)
• Succinylcholine, similar neuromuscular blockers and cholinergic agonists such as bethanechol (label): Effects add up rather than cancelling, which matters most around surgery and anaesthesia - the combination can produce excessive cholinergic effect. (Source 6)
• Ketoconazole and other strong CYP3A4 inhibitors (pharmacokinetic study): A 7-day crossover study in 18 healthy volunteers found ketoconazole raised donepezil exposure (AUC and peak concentration) by 36%; the same label sentence adds that the clinical relevance of that rise is unknown. The quote stops before the parenthetical because the rendered label sets AUC and Cmax as subscripts, which breaks a literal text search. (Source 7)
• CYP3A4 inducers (phenytoin, carbamazepine, dexamethasone, rifampin, phenobarbital) (label): These speed up the clearance of donepezil, which could lower its blood level. Note this is the same enzyme St John's wort induces, though St John's wort itself is not named in the donepezil label and we found no donepezil-specific study of it. (Source 7)
• Food (pharmacokinetic study): No interaction: food does not change how much donepezil is absorbed or how fast. It can be taken with or without a meal. (Source 7)
• Alcohol-related liver disease (pharmacokinetic study): No pharmacokinetic interaction with alcohol itself is described in the label. What is described is that established alcoholic cirrhosis slows donepezil clearance by about a fifth, so liver damage from long-term drinking can raise exposure. (Source 7)

Stopping it

• The best single trial of stopping is DOMINO-AD, which randomised 295 people with moderate-to-severe Alzheimer's disease, all already on donepezil for at least three months, to continue or stop. Over 12 months those who continued scored 1.9 SMMSE points higher and 3.0 BADLS points better; the cognitive difference was larger than the 1.4-point threshold the trialists had set in advance as clinically important. (Source 8)
• Pooling seven withdrawal trials (759 people randomised, abrupt stopping in five of them and stepwise in two), Cochrane reached the same direction of effect but rated nearly all of it low or very low certainty, and found no clear effect on adverse events or deaths from stopping. (Source 9)
• That review's authors note the findings only apply to Alzheimer's disease, that they could not tell whether dementia severity changes the answer, and that there is no evidence at all to guide stopping memantine. (Source 9)
• Donepezil is not a controlled substance and we found no description of a physical dependence or withdrawal syndrome. What the trials describe is loss of the symptomatic benefit. The toxic picture runs the other way: too much cholinesterase inhibition produces a cholinergic crisis, treated with atropine. (Source 10)

What goes wrong

More people on donepezil had an adverse event or dropped out of the trial than on placebo. (Source 2)

• Systematic review, Moderate certainty.
• Size: 2,846 participants across 12 studies (withdrawal); 2,500 across 10 studies (adverse events)
• Who: people with dementia due to Alzheimer's disease.
• How long: 24 to 26 weeks.
• Result: withdrawal before end of treatment 24% vs 20% (OR 1.25, 95% CI 1.05 to 1.50); any adverse event 72% vs 65% (OR 1.59, 95% CI 1.31 to 1.95)
• Funding: majority industry funded or sponsored.

Limit of this finding: The published review omits two letters here: it prints '95% 1.31 to 1.95' where it means '95% CI 1.31 to 1.95'. The numbers are the confidence interval for the odds ratio of 1.59 and are correct as printed. The omission is the journal's and has been left in the quotation rather than silently corrected.

Participants receiving donepezil were more likely to withdraw from the studies before the end of treatment (24% versus 20%, OR 1.25, 95% CI 1.05 to 1.50, 2846 participants, 12 studies) or to experience an adverse event during the studies (72% vs 65%, OR 1.59, 95% 1.31 to 1.95, 2500 participants, 10 studies).

The label's own trial data show the 23 mg dose more than doubled the rate of stopping for side effects compared with 10 mg. (Source 11)

• Official position, Certainty not rated.
• Size: 963 patients on 23 mg/day and 471 on 10 mg/day in one controlled trial.
• Who: people with moderate to severe Alzheimer's disease.
• How long: 24 weeks.
• Result: discontinuation for adverse reactions 19% on 23 mg/day vs 8% on 10 mg/day; most discontinuations in the first month.
• Funding: regulatory label (manufacturer-submitted data), Eisai Inc., SPL version 33, published 30 June 2026.

The rate of discontinuation from a controlled clinical trial of ARICEPT 23 mg/day due to adverse reactions was higher (19%) than for the 10 mg/day treatment group (8%).

In severe Alzheimer's disease trials the label reports 12% of people on donepezil stopped for adverse reactions versus 7% on placebo. (Source 11)

• Official position, Certainty not rated.
• Size: over 600 patients with severe Alzheimer's disease across trials of at least 6 months, including three placebo-controlled trials.
• Who: people with severe Alzheimer's disease.
• How long: at least 6 months.
• Result: discontinuation for adverse reactions about 12% vs 7% placebo; anorexia 2% vs 1%, nausea 2% vs under 1%, diarrhea 2% vs 0%, urinary tract infection 2% vs 1%.
• Funding: regulatory label (manufacturer-submitted data)

The rates of discontinuation from controlled clinical trials of ARICEPT due to adverse reactions for the ARICEPT patients were approximately 12% compared to 7% for placebo patients. The most common adverse reactions leading to discontinuation, defined as those occurring in at least 2% of ARICEPT patients and at twice or more the incidence seen in placebo, were anorexia (2% vs. 1% placebo), nausea (2% vs. <1% placebo), diarrhea (2% vs. 0% placebo), and urinary tract infection (2% vs. 1% placebo).

In mild cognitive impairment the drugs caused clearly more gastrointestinal and other side effects without serious harm or death increasing. (Source 3)

• Systematic review, Low certainty.
• Size: 4,207 individuals for the adverse event analysis.
• Who: people with mild cognitive impairment.
• How long: one to three years.
• Result: any adverse event RR 1.09 (95% CI 1.02 to 1.16); diarrhoea RR 2.10 (1.30 to 3.39); nausea RR 2.97 (2.57 to 3.42); vomiting RR 4.42 (3.23 to 6.05); muscle spasms/leg cramps RR 7.52 (4.34 to 13.02); syncope or dizziness RR 1.62 (1.36 to 1.93); insomnia RR 1.66 (1.36 to 2.02); abnormal dreams RR 4.25 (2.57 to 7.04); no increase in serious adverse events, deaths or cardiac problems (RR 0.71, 0.25 to 2.02)
• Funding: not stated in the abstract; Cochrane review.

Limit of this finding: The review says there is no strong evidence that these drugs slow progression to dementia and then reports a two-year risk ratio of 0.67 (95% CI 0.55 to 0.83), which does exclude no effect. The review explains the apparent clash in the same breath: that result comes from only two studies reported in a single article. The two statements belong together and neither should be quoted without the other.

Based on the results from 4207 individuals, there were significantly more adverse events in the cholinesterase inhibitor groups (RR 1.09; 95% CI 1.02 to 1.16), but no more serious adverse events or deaths. Gastrointestinal side effects were much more common (diarrhoea: RR 2.10; 95% CI 1.30 to 3.39; nausea: RR 2.97; 95% CI 2.57 to 3.42; vomiting: RR 4.42; 95% CI 3.23 to 6.05).

People with dementia taking cholinesterase inhibitors had higher rates of syncope, bradycardia, permanent pacemaker insertion and hip fracture than untreated controls. (Source 12)

• Cohort study, Low certainty.
• Size: 19,803 community-dwelling older adults on cholinesterase inhibitors and 61,499 controls.
• Who: community-dwelling older adults with dementia in Ontario, Canada, 2002-2004.
• How long: two-year accrual with follow-up.
• Result: syncope hospital visits 31.5 vs 18.6 per 1000 person-years (adjusted HR 1.76, 95% CI 1.57-1.98); bradycardia 6.9 vs 4.4 (HR 1.69, 1.32-2.15); pacemaker insertion 4.7 vs 3.3 (HR 1.49, 1.12-2.00); hip fracture 22.4 vs 19.8 (HR 1.18, 1.04-1.34)
• Funding: not stated in the abstract.

Hospital visits for syncope were more frequent in people receiving cholinesterase inhibitors than in controls (31.5 vs 18.6 events per 1000 person-years; adjusted hazard ratio [HR], 1.76; 95% confidence interval [CI], 1.57-1.98). Other syncope-related events were also more common among people receiving cholinesterase inhibitors compared with controls: hospital visits for bradycardia (6.9 vs 4.4 events per 1000 person-years; HR, 1.69; 95% CI, 1.32-2.15), permanent pacemaker insertion (4.7 vs 3.3 events per 1000 person-years; HR, 1.49; 95% CI, 1.12-2.00), and hip fracture (22.4 vs 19.8 events per 1000 person-years; HR, 1.18; 95% CI, 1.04-1.34).

The authors of that cohort study judged these harms had been underrecognised and had to be set against benefits they described as generally modest. (Source 13)

• Cohort study, Low certainty.
• Size: 81,302 people in total.
• Who: older adults with dementia.
• How long: two-year accrual.
• Result: no new numbers; authors' overall judgement.
• Funding: not stated in the abstract.

Use of cholinesterase inhibitors is associated with increased rates of syncope, bradycardia, pacemaker insertion, and hip fracture in older adults with dementia.

Post-marketing reports for donepezil include heart block of all types, QTc prolongation and torsade de pointes, with frequency unknown. (Source 10)

• Case series, Very low certainty.
• Size: not quantifiable - spontaneous reports from a population of uncertain size.
• Who: people taking donepezil after approval.
• How long: not applicable.
• Result: no rates can be calculated; reported events include heart block (all types), QTc prolongation, torsade de pointes, convulsions, hepatitis, hyponatremia, neuroleptic malignant syndrome, pancreatitis, rhabdomyolysis.
• Funding: regulatory label (manufacturer-collected spontaneous reports)

Overdosage with cholinesterase inhibitors can result in cholinergic crisis characterized by severe nausea, vomiting, salivation, sweating, bradycardia, hypotension, respiratory depression, collapse, and convulsions.

What the evidence supports

At 26 weeks donepezil 10 mg a day gave small advantages over placebo on three different cognitive scales and on clinician-rated global change. (Source 2)

• Systematic review, Moderate certainty.
• Size: 3,396 participants in the main 24-to-26-week analysis, from 13 studies (30 studies, 8,257 participants in the whole review)
• Who: people with mild, moderate or severe dementia due to Alzheimer's disease, mean age about 75.
• How long: 24 to 26 weeks in the main analysis; most studies six months or less, only one lasted 52 weeks.
• Result: ADAS-Cog (0-70) MD -2.67 (95% CI -3.31 to -2.02); MMSE MD 1.05 (95% CI 0.73 to 1.37); Severe Impairment Battery (0-100) MD 5.92 (95% CI 4.53 to 7.31); clinician-rated global improvement OR 1.92 (95% CI 1.54 to 2.39)
• Funding: 17 of 30 studies industry funded or sponsored, 4 independent, 9 unstated; evidence downgraded for study limitations.

After 26 weeks of treatment, donepezil compared with placebo was associated with better outcomes for cognitive function measured with the Alzheimer's Disease Assessment Scale-Cognitive (ADAS-Cog, range 0 to 70) (mean difference (MD) -2.67, 95% confidence interval (CI) -3.31 to -2.02, 1130 participants, 5 studies), the Mini-Mental State Examination (MMSE) score (MD 1.05, 95% CI 0.73 to 1.37, 1757 participants, 7 studies) and the Severe Impairment Battery (SIB, range 0 to 100) (MD 5.92, 95% CI 4.53 to 7.31, 1348 participants, 5 studies).

Continuing donepezil in moderate-to-severe Alzheimer's disease preserved cognition and function compared with stopping it, over 12 months. (Source 8)

• Randomized trial, Moderate certainty.
• Size: 295 community-dwelling patients.
• Who: people already on donepezil at least 3 months with moderate or severe Alzheimer's disease (SMMSE 5 to 13)
• How long: 52 weeks.
• Result: continuing vs discontinuing: SMMSE higher by 1.9 points (95% CI 1.3 to 2.5); BADLS lower (less impairment) by 3.0 points (95% CI 1.8 to 4.3), both P<0.001; the SMMSE difference exceeded the pre-set minimum clinically important difference of 1.4 points.
• Funding: UK Medical Research Council and UK Alzheimer's Society (independent of industry)

Patients assigned to continue donepezil, as compared with those assigned to discontinue donepezil, had a score on the SMMSE that was higher by an average of 1.9 points (95% confidence interval [CI], 1.3 to 2.5) and a score on the BADLS that was lower (indicating less impairment) by 3.0 points (95% CI, 1.8 to 4.3) (P<0.001 for both comparisons).

What the evidence does not support

Donepezil made no measurable difference to behavioural and psychiatric symptoms of dementia or to quality of life. (Source 2)

• Systematic review, Moderate certainty.
• Size: 1,035 participants across 4 studies (NPI); 194 in 1 study (BEHAVE-AD); 815 across 2 studies (quality of life)
• Who: people with dementia due to Alzheimer's disease.
• How long: 24 to 26 weeks.
• Result: NPI MD -1.62 (95% CI -3.43 to 0.19); BEHAVE-AD MD 0.4 (95% CI -1.28 to 2.08); quality of life MD -2.79 (95% CI -8.15 to 2.56)
• Funding: majority industry funded or sponsored (17 of 30 studies)

There was no difference between donepezil and placebo for behavioural symptoms measured by the Neuropsychiatric Inventory (NPI) (MD -1.62, 95% CI -3.43 to 0.19, 1035 participants, 4 studies) or by the Behavioural Pathology in Alzheimer's Disease (BEHAVE-AD) scale (MD 0.4, 95% CI -1.28 to 2.08, 194 participants, 1 study). There was also no difference between donepezil and placebo for Quality of Life (QoL) (MD -2.79, 95% CI -8.15 to 2.56, 815 participants, 2 studies).

The 23 mg dose gave no extra benefit over 10 mg but produced more adverse events and withdrawals. (Source 2)

• Systematic review, Moderate certainty.
• Size: 2 studies comparing 10 mg/day with 23 mg/day.
• Who: people with moderate to severe Alzheimer's disease.
• How long: 26 weeks.
• Result: no differences on efficacy outcomes; fewer adverse events and withdrawals on 10 mg/day.
• Funding: industry sponsored (the 23 mg formulation studies)

Two studies compared donepezil 10 mg/day to donepezil 23 mg/day. There were no differences on efficacy outcomes, but fewer participants on 10 mg/day experienced adverse events or withdrew from treatment.

Cholinesterase inhibitors did not improve cognitive test scores in mild cognitive impairment and gave no strong evidence of slowing progression to dementia. (Source 3)

• Systematic review, Low certainty.
• Size: 5,149 individuals across 9 studies (3 studies reported conversion to dementia)
• Who: people with mild cognitive impairment, however defined.
• How long: one to three years.
• Result: RR for conversion to dementia at two years 0.67 (95% CI 0.55 to 0.83) but from only two studies in a single article; essentially no effect on cognitive test scores.
• Funding: not stated in the abstract; Cochrane review.

Limit of this finding: The review says there is no strong evidence that these drugs slow progression to dementia and then reports a two-year risk ratio of 0.67 (95% CI 0.55 to 0.83), which does exclude no effect. The review explains the apparent clash in the same breath: that result comes from only two studies reported in a single article. The two statements belong together and neither should be quoted without the other.

Meta-analysis of the three studies reporting conversion to dementia gives no strong evidence of a beneficial effect of cholinesterase inhibitors on the progression to dementia at one, two or three years. The risk ratio (RR) for conversion at two years was significantly different from unity (0.67; 95% confidence interval (CI) 0.55 to 0.83), but this is based on only two studies reported in the same article. There was essentially no effect of cholinesterase inhibitors on cognitive test scores.

Adding memantine to donepezil gave no significant extra benefit over donepezil alone. (Source 8)

• Randomized trial, Moderate certainty.
• Size: 295 patients in a four-arm factorial trial.
• Who: people with moderate or severe Alzheimer's disease.
• How long: 52 weeks.
• Result: no significant benefit of the combination over donepezil alone; memantine's own effect 1.2 SMMSE points (95% CI 0.6 to 1.8) was below the 1.4-point minimum clinically important difference.
• Funding: UK Medical Research Council and UK Alzheimer's Society (independent of industry)

The efficacy of donepezil and of memantine did not differ significantly in the presence or absence of the other. There were no significant benefits of the combination of donepezil and memantine over donepezil alone.

Stopping a cholinesterase inhibitor did not clearly change adverse events, serious adverse events or deaths. (Source 14)

• Systematic review, Low certainty.
• Size: 759 participants randomised across 7 trials.
• Who: people with dementia due to Alzheimer's disease.
• How long: 6 weeks to 12 months.
• Result: dropout for lack of efficacy or deterioration OR 1.53 (95% CI 0.84 to 2.76); adverse events OR 0.85 (0.57 to 1.27); serious adverse events OR 0.80 (0.46 to 1.39); mortality OR 0.75 (0.36 to 1.55), all low certainty.
• Funding: not stated in the abstract; Cochrane review.

Limit of this finding: Two of the review's certainty labels do not follow its own convention. It describes the 12-month neuropsychiatric result with 'may', which Cochrane uses for low certainty, while labelling it moderate certainty; and it calls a medium-term functional result very uncertain although its interval (-0.74 to -0.01) excludes no effect. These labels are judgements about how far the evidence can be trusted, not arithmetic errors in the estimates.

We found no clear evidence of an effect of discontinuation on dropout due to lack of medication efficacy or deterioration in overall medical condition (odds ratio (OR) 1.53, 95% CI 0.84 to 2.76; 4 studies; low certainty), on number of adverse events (OR 0.85, 95% CI 0.57 to 1.27; 4 studies; low certainty) or serious adverse events (OR 0.80, 95% CI 0.46 to 1.39; 4 studies; low certainty), and on mortality (OR 0.75, 95% CI 0.36 to 1.55; 5 studies; low certainty).

Where the evidence is mixed

In vascular cognitive impairment donepezil improved cognition, but the reviewers said the size of the change is unlikely to matter clinically. (Source 4)

• Systematic review, High certainty.
• Size: 4,373 participants across 8 trials; donepezil trials 2,193 participants.
• Who: adults with possible or probable vascular dementia or cognitive impairment after stroke, mean age 72 to 74.
• How long: not stated in the abstract.
• Result: donepezil 5 mg MD -0.92 ADAS-Cog points (95% CI -1.44 to -0.40, high certainty); donepezil 10 mg MD -2.21 (95% CI -3.07 to -1.35, moderate certainty); adverse events donepezil 10 mg vs placebo OR 1.95 (95% CI 1.20 to 3.15, high certainty)
• Funding: not stated in the abstract; Cochrane review with GRADE.

For cognition, the results showed that donepezil 5 mg improves cognition slightly, although the size of the effect is unlikely to be clinically important (mean difference (MD) -0.92 Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog) points (range 0 to 70), 95% confidence interval (CI) -1.44 to -0.40; high-certainty evidence). Donepezil 10 mg (MD -2.21 ADAS-Cog points, 95% CI -3.07 to -1.35; moderate-certainty evidence) and galantamine 16 to 24 mg (MD -2.01 ADAS-Cog point, 95%CI -3.18 to -0.85; moderate-certainty evidence) probably also improve cognition, although the larger effect estimates still may not be clinically important.

Pooled withdrawal trials suggest stopping a cholinesterase inhibitor worsens cognition, function and neuropsychiatric symptoms, but the evidence is almost all low or very low certainty. (Source 14)

• Systematic review, Low certainty.
• Size: 759 participants randomised across 7 trials (6 on cholinesterase inhibitor withdrawal)
• Who: people with dementia due to Alzheimer's disease, mild to very severe, tolerating treatment at baseline.
• How long: 6 weeks to 12 months.
• Result: short-term cognition SMD -0.42 (95% CI -0.64 to -0.21, low certainty); at 12 months MD -2.09 SMMSE points (95% CI -3.43 to -0.75, moderate certainty); function at 12 months MD -3.38 BADLS points (95% CI -6.67 to -0.10, moderate certainty); no clear effect on adverse events (OR 0.85, 0.57 to 1.27) or mortality (OR 0.75, 0.36 to 1.55)
• Funding: not stated in the abstract; Cochrane review. Some studies at unclear or high risk of bias.

Limit of this finding: Two of the review's certainty labels do not follow its own convention. It describes the 12-month neuropsychiatric result with 'may', which Cochrane uses for low certainty, while labelling it moderate certainty; and it calls a medium-term functional result very uncertain although its interval (-0.74 to -0.01) excludes no effect. These labels are judgements about how far the evidence can be trusted, not arithmetic errors in the estimates.

Compared to continuing cholinesterase inhibitors, discontinuing treatment may be associated with worse cognitive function in the short term (standardised mean difference (SMD) -0.42, 95% confidence interval (CI) -0.64 to -0.21; 4 studies; low certainty), but the effect in the medium term is very uncertain (SMD -0.40, 95% CI -0.87 to 0.07; 3 studies; very low certainty).

Where the research disagrees

Whether donepezil's measured benefit is big enough to matter to a person

• FDA label (Eisai Inc., published 30 June 2026), regulatory position based on manufacturer-submitted trials: ARICEPT is indicated for the treatment of dementia of the Alzheimer’s type. Efficacy has been demonstrated in patients with mild, moderate, and severe Alzheimer (Source 15)
• Cochrane review of cholinesterase inhibitors in vascular cognitive impairment (2021), network meta-analysis of 8 randomised trials, GRADE high certainty for the donepezil 5 mg estimate: donepezil 5 mg improves cognition slightly, although the size of the effect is unlikely to be clinically important (Source 4)
• Cochrane review of donepezil in Alzheimer's disease (2018), systematic review of 30 trials, 8,257 participants, moderate-quality evidence: treated for periods of 12 or 24 weeks with donepezil experience small benefits in cognitive function, activities of daily living and clinician-rated global clinical state. (Source 16)

Whether cholinesterase inhibitors should be used for mild cognitive impairment

• Cochrane review of cholinesterase inhibitors for mild cognitive impairment (2012), systematic review of 9 double-blind placebo-controlled trials, 5,149 people: This weak evidence is overwhelmed by the increased risk of adverse events, particularly gastrointestinal. Cholinesterase inhibitors should not be recommended for mild cognitive impairment. (Source 17)
• The same review, on the one signal that pointed the other way, two trials reported in a single article within the same systematic review: The risk ratio (RR) for conversion at two years was significantly different from unity (0.67; 95% confidence interval (CI) 0.55 to 0.83), but this is based on only two studies reported in the same article. (Source 3)

How much

• Reference intake: Dosing is set by the prescriber. As a position, the Aricept label (Eisai Inc., SPL version 33, published 30 June 2026) states a starting dose of 5 mg once a day in the evening, with 10 mg not given until 5 mg has been taken for 4 to 6 weeks. (Source 18)
• Upper limit: As a position, the same label gives a maximum of 10 mg a day for mild to moderate Alzheimer's disease and 23 mg a day for moderate to severe disease, with 23 mg not given until 10 mg has been taken for at least 3 months. There is no population reference intake or upper intake level - donepezil is a prescription medicine, not a nutrient. (Source 18)
• Studied: The trials pooled in the 2018 Cochrane review mainly tested donepezil capsules at 5 mg/day or 10 mg/day, with two studies of a slow-release 23 mg/day formulation. (Source 2)
• Studied: The Cochrane vascular cognitive impairment network meta-analysis included donepezil 5 mg or 10 mg daily in three trials (2,193 participants). (Source 4)
• Studied: DOMINO-AD enrolled people already taking donepezil for at least 3 months and randomised them to continue or discontinue it over 52 weeks. (Source 19)

A common belief, and what the research shows

The belief: Donepezil slows down or treats Alzheimer's disease itself.

What the research shows: The label says the opposite in one sentence: "There is no evidence that donepezil alters the course of the underlying dementing process." What the trials show is a symptomatic effect of a few points on cognitive scales, which Cochrane describes as "small benefits in cognitive function, activities of daily living and clinician-rated global clinical state" over 12 to 24 weeks. Behavioural symptoms and quality of life did not improve at all compared with placebo.

Questions and answers

What is it?

Donepezil is a once-daily tablet that blocks acetylcholinesterase, the enzyme that destroys the neurotransmitter acetylcholine. It is not a nutrient or anything the body makes - it is a synthetic medicine. In the United States it is approved for dementia of the Alzheimer's type at mild, moderate and severe stages, and it is also widely prescribed off-label for other dementias. (Source 15)

What does it do in the body?

Alzheimer's disease damages cholinergic nerve cells, so less acetylcholine is available for signalling. Donepezil reversibly blocks the enzyme that breaks acetylcholine down, which raises its concentration at the synapse and partly compensates. The label states directly that there is no evidence the drug changes the underlying disease process. (Source 1)

Is it good or bad for you?

It depends on the setting. In Alzheimer's dementia, moderate-quality evidence from 30 trials shows small benefits in cognition, daily function and clinician-rated global state - real but modest, and not disease-modifying. In mild cognitive impairment the same class of drug showed essentially no cognitive benefit and Cochrane concluded it should not be recommended there. Harms are consistent across settings: more nausea, diarrhoea, insomnia and cramps, and in a large cohort more syncope, bradycardia, pacemakers and hip fractures. (Source 16)

How do you get more of it?

Donepezil is prescription-only; there is no food, supplement or behaviour that provides it. Dose is the prescriber's decision and the label's schedule is deliberately slow: 5 mg a day to start, 10 mg only after 4 to 6 weeks at 5 mg, and 23 mg only after at least 3 months at 10 mg. In the trials the higher dose bought no extra benefit and caused more side effects, so more is not better. (Source 18)

If it is harmful, what reduces it?

When there is too much cholinergic effect - a cholinergic crisis with severe nausea, vomiting, salivation, sweating, slow heart rate, low blood pressure and possible convulsions - the antidote is a tertiary anticholinergic, atropine, given intravenously and titrated to effect. For ordinary dose-related side effects, the Cochrane review found fewer adverse events and withdrawals at lower doses, so dose reduction is the usual route. It is not known whether dialysis removes donepezil. (Source 10)

Why might someone be low in it or missing it?

Nobody is naturally low in donepezil; it is a medicine. People are not on it either because their dementia has not been diagnosed or is not of a type it is used for, because side effects stopped it (12% of people in the severe-disease trials versus 7% on placebo), or because it was deliberately deprescribed. Its blood level can also be reduced by enzyme-inducing drugs such as phenytoin, carbamazepine and rifampin. (Source 11)

Which whole foods contain it or feed it?

No whole food contains donepezil, and none is known to raise or lower it meaningfully. The only food-related finding in the label is a negative one: meals do not change how much of the drug is absorbed or how quickly, so it can be taken with or without food. (Source 7)

What happens if you do not have it?

For someone who has never taken it, nothing happens - it is not something the body needs. For someone already taking it, stopping is a measured event: in DOMINO-AD, people who stopped donepezil lost about 1.9 SMMSE points of cognition and 3.0 BADLS points of daily function over 12 months compared with those who continued, and the cognitive gap was larger than the threshold the trialists had set as clinically important. (Source 8)

How can you test for it?

There is no blood test that says whether someone needs donepezil or whether it is working. What the trials used were rating scales: the ADAS-Cog (0 to 70), the MMSE, the Severe Impairment Battery (0 to 100) for advanced disease, and activities-of-daily-living scales - all observer- or examiner-administered, and all sensitive to who is doing the rating. The changes donepezil produces on these scales are a few points, smaller than the within-person variation many of these instruments show. (Source 2)

References

1. DailyMed / Eisai Inc. (SPL version 33, published 30 June 2026). ARICEPT (donepezil hydrochloride) tablet - FDA label, section 12.1 Mechanism of Action. 2026. Read the source
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