A randomized, placebo controlled, double-blind, parallel group Phase 3 design will be used to assess the effect of 24 weeks of donepezil on cognitive function (memory) in breast cancer survivors who report having cognitive dysfunction and demonstrate memory impairment 1-5 year post chemotherapy. Patients who meet the eligibility criteria will be stratified by age (<50, 50-59, 60-69, ≥70) and randomized to donepezil or placebo with equal probability.