<p>Drugs with anticholinergic properties and which cross into the brain, such as atropine, benztropine produce the opposite effects of Donepezil and should be avoided during therapy with donepezil. Medication with carbamazepine, dexamethasone, phenobarbital, phenytoin may reduce the effect of donepezil whereas ketoconazole, quinidine, cimetidine may increase the effects.</p>