Donepezil-d7 hydrochloride is primarily used in research and development as an internal standard in analytical chemistry. It aids in the accurate quantification and detection of donepezil in biological samples through techniques like mass spectrometry. This deuterated compound ensures precision in pharmacokinetic studies, helping researchers understand the absorption, distribution, metabolism, and excretion of donepezil in the body. It is also valuable in clinical studies to monitor therapeutic drug levels and optimize dosage regimens for patients with Alzheimer's disease.