While adverse reactions to donepezil are uncommon, some patients who take the drug may experience mild side effects, including diarrhea, nausea, headache, dizziness, and drowsiness. These effects usually go away within 1-3 weeks as your body adjusts to the medication. Tell your healthcare provider if any of these are severe or don’t go away.
Severe side effects are rare but may occur. Get immediate medical attention if you experience any severe abdominal pain, black stools, vomit that looks like coffee grounds, seizures, trouble urinating, or signs of an allergic reaction (such as rash; hives; itching; swelling of the face, mouth, or throat; or trouble breathing or swallowing).
Talk to your doctor about your medical history - particularly if you have or have ever had bleeding in your stomach or intestines; an ulcer; irregular, slow, or fast heartbeat; seizures; difficulty urinating; asthma; chronic obstructive pulmonary disease (COPD); or kidney, liver, or heart disease.
Inform your doctor of all known allergies and of all medications, supplements, and herbal products that you take. Tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding.
This is not a complete list of side effects or precautions. For more information please visit the National Institutes of Health’s DailyMed webpage for Donepezil.