An 85-year-old lady with a 4-year history of Alzheimer's dementia was started on a dose of 5 mg of Donepezil. Improvements were noted in her overall mental state with an associated reduction in the level of carer stress but with mild and transient subjective gastrointestinal complaints. Therefore, the dose was cautiously increased to 10 mg. But within 10 days of the increase, she reported bilateral leg pain severe enough to cause her mental state to deteriorate significantly. Pain induced by Donepezil undermined the efficacy of the drug, resulted in increased carer stress and worsening cognition not reversed by the change of medication to another cholinesterase inhibitor.