Phase 3 Randomized Placebo Controlled Clinical Trial of Donepezil

Inclusion Criteria: * Women ≥18 years old with history of invasive breast cancer * Must have completed at least 4 cycles of adjuvant/neo-adjuvant cytotoxic chemotherapy between 1 and 5 years prior to registration (Ongoing herceptin or other chronic human epidermal growth factor receptor 2 (HER2) directed therapies are allowed). * Patients receiving ongoing hormonal therapy for breast cancer must be on the same hormonal agent for at least 3 months prior to study registration and plan to continue for the duration of the study (9 months) * Use of psychotropic medications (anti-depressants, anxiolytics, sleeping aids, narcotics) is permitted (patient will be asked to list any that have been taken within the last 3 days on the recent medication sheet) if dose is stable over previous 12 weeks. Patients who were previously on one of these psychotropic medications and have subsequently discontinued the drug must have been off the medication for at least 4 weeks prior to enrollment. Patients who have been on a psychotropic medication for at least 12 weeks but have recently switched to a medicine in the same class (for example, switching from one selective serotonin reuptake inhibitor (SSRI) antidepressant to a different SSRI antidepressant) need to be on a stable dose of the new medication for at least 4 weeks prior to enrollment to be eligible. * Self-reported cognitive problem plus a measured memory deficit (score \<7 on single trial of Eligibility Pre-screen Hopkins Verbal Learnin…