The hydrochloride salt of a piperidine derivative with neurocognitive-enhancing activity. Donepezil reversibly inhibits acetylcholinesterase, thereby blocking the hydrolysis of the neurotransmitter acetylcholine and, consequently, increasing its activity. This agent may improve neurocognitive function in Alzheimer's disease, reduce sedation associated with opioid treatment of cancer pain, and improve neurocognitive function in patients who have received radiation therapy for primary brain tumors or brain metastases.