- Visit 4 (week 16): Patients will repeat the evaluations done during visit 2 and will have their study medication switched. That is, patients previously on placebo will be switched to donepezil, and patients who were taking donepezil will be switched to placebo. After 4 weeks, the dose of donepezil will be increased to 10 mg per day. Patients who do not tolerate the higher dose will have it reduced to 5 mg. Those who do not tolerate the 5-mg dose will be taken off medication but will continue to be followed and tested.