Alzheimer’s disease and some other dementias involve a drop in acetylcholine, a brain chemical needed for memory and thinking.
AChEIs work by slowing the breakdown of acetylcholine, giving brain cells a little more of this chemical to use.
Multiple randomized clinical trials and systematic reviews (including Cochrane analyses) show about 1 in 5–8 patients (12-20%) experience a noticeable, small, consistent, benefit that wouldn’t have occurred without the drug.
The statistically significant, but modest improvements, are:
Average improvement of 2–3 points on a 70-point memory/thinking tests (ADAS-Cog scale).
For mild AD: a change of +3 points on the ADAS-Cog is often meaningful.
For mild cognitive impairment: a 2-3 point change on the ADAS-Cog is often considered a minimal clinically important difference
A 2-3 change impacts areas such memory, language, or the application of knowledge and ideas, which directly impact daily life, such as:
Dressing with less help
Eating
Handling finances
Having a little more clarity
Being in a better mood
Steadier daily routine
Following a conversation a bit better
Remembering appointments

0–18 MONTHS (STRONG EVIDENCE):
Randomized clinical trials consistently show modest benefits on thinking, daily function, and global measures within the first 6–18 months.
1.5–3 YEARS (MODERATE EDVIDENCE):
Extension and observational studies suggest benefits often continue for 2–3 years, though effects usually shrink over time.
GREATER THAN 3 YEARS (LIMITED EVIDENCE):
Some long-term observational data suggest ongoing small benefits or slower decline, but the evidence is weaker and may be affected by other factors.
WHAT TO EXPECT:
Most people see the clearest benefit in the first year; some continue to do better than expected for several years. These medicines slow decline rather than cure the disease.
INDIVIDUAL VARIATION:
Responses vary widely—some people show noticeable changes, others show only small slowing of decline. Side effects and overall health influence continuation.
Side effects are most likely when first starting or increasing the dose, and may improve over time.
Nausea, vomiting, diarrhea, appetite loss, weight loss (studies show ~1 in 20 patients may lose 10 or more pounds in a year), muscle cramps, insomnia, and vivid dreams
Serious but less common:
Slow heart rate, fainting and increased risk of falls in frail elders