Before taking donepezil, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details. Before using this medication, tell your doctor or pharmacist your medical history, especially of: breathing problems (such as asthma, chronic obstructive pulmonary disease), fainting, seizures, stomach/intestinal disease (such as ulcers, bleeding), trouble urinating (such as enlarged prostate). Low levels of potassium or magnesium in the blood may also increase your risk of QT prolongation. This risk may increase if you use certain drugs (such as diuretics/”water pills”) or if you have conditions such as severe sweating, diarrhea, or vomiting. Talk to your doctor about using donepezil safely. It is unknown if this drug passes into breast milk. Consult your doctor before breast-feeding. Some products that may interact with this drug include: aspirin/non-steroidal anti-inflammatory drugs (NSAIDs, such as ibuprofen, naproxen).