Donepezil. Computer model of a molecule of the drug donepezil. It is sold under the brand name Aricept. It is an acetylcholinesterase inhibitor drug, used to treat Alzheimer's disease by increasing levels of the neurotransmitter acetylcholine. The molecule's chemical formula is C24.H29.N.O3. Atoms (spheres) are colour-coded: carbon (grey), hydrogen (light blue), nitrogen (dark blue), oxygen (orange).