Diarrhea, nausea, vomiting, loss of appetite, increased weight, loss of bladder control, back pain, headache, bruising, drowsiness, or dizziness may occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly. Remember that this medication has been prescribed because your doctor has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects. Tell your doctor right away if you have any serious side effects, including: signs of stomach/intestinal bleeding (such as black/bloody stools, vomit that contains blood or looks like coffee grounds, stomach/abdominal pain), difficulty urinating, mental/mood changes (such as depression, aggression). Get medical help right away if you have any very serious side effects, including: fast/slow/irregular heartbeat, severe dizziness, fainting, seizures. A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing. This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist. In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch. In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Some products that may interact with this drug include: carbonic anhydrase inhibitors (such as acetazolamide, methazolamide), sodium bicarbonate, aspirin/non-steroidal anti-inflammatory drugs (NSAIDs, such as ibuprofen, naproxen). Check all prescription and nonprescription medicine labels carefully since many medications contain pain relievers/fever reducers (aspirin, NSAIDs such as ibuprofen or naproxen) that if taken together with donepezil may increase your risk for stomach/intestinal bleeding. However, if your doctor has told you to take low-dose aspirin to prevent heart attack or stroke (usually 81-162 milligrams a day), you should keep taking the aspirin unless your doctor tells you not to. Ask your doctor or pharmacist for more details.