A nurse is assessing a client who has a prescription for haloperidol 0.5 mg PO three times daily. The medication administration record shows that the client received 5 mg per dose on the previous day. Which of the following manifestations is the nurse's priority to assess?

A. Muscle stiffness can indicate extrapyramidal symptoms or early neuroleptic malignant syndrome, which are potentially life-threatening complications of haloperidol overdose. Prompt assessment and intervention are critical to prevent serious harm. B. Constipation is a common side effect of haloperidol due to anticholinergic effects, but it develops gradually and is not immediately dangerous. C. Dry mouth is also an anticholinergic side effect, causing discomfort but not posing an acute threat to the client’s safety. D. Daytime drowsiness is a frequent effect of haloperidol, especially at high doses, but it is less immediately dangerous than neuromuscular complications.