Which option is a cholinesterase inhibitor?

• A. Memantine
• B. Quetiapine
• C. Donepezil
• D. Gabapentin

Answer: (C)

Cholinesterase inhibitors raise brain acetylcholine by blocking the enzyme that breaks it down, strengthening cholinergic signaling important for memory and learning. Donepezil is a reversible acetylcholinesterase inhibitor that crosses into the brain and is commonly used to help manage cognitive symptoms of Alzheimer's disease. The other drugs act through different mechanisms: memantine modulates glutamate signaling at NMDA receptors, quetiapine is an atypical antipsychotic, and gabapentin affects calcium channels with uses in neuropathic pain and seizures. Therefore, donepezil is the cholinesterase inhibitor.