Those count as "undiscovered" too - undiscovered by at least me. :)

This article cited by Luke has more nuanced appreciations of drugs like Donepezil, and generally a more balanced take on the subject. For instance, they report that

Detrimental effects on cognition have also been reported: both in healthy young participants (Beglinger QJ et al., 2004) and in healthy elderly volunteers (Beglinger et al., 2005), donepezil administration (5 mg for 14 days and 10 mg for 14 days respectively) caused a slight deterioration of performance on speed, attention and short-term memory tasks.

The same article goes on to suggest that perhaps 14 days is too short a timeframe for the beneficial effects to be felt. However one can also find studies like this one (not cited by Luke) which show detrimental effects on cognition in healthy subjects over four weeks of treatment.

Neither Luke nor de Jongh et al. report on the frequent side-effects, which (Wikipedia says) include bradycardia, nausea, diarrhea, anorexia, abdominal pain, and vivid dreams.