A client who is newly diagnosed with diabetes insipidus (DI) is receiving a synthetic vasopressin IV. Which side effect of vasopressin reported by the client should the nurse report to the healthcare provider?

A. Low urine specific gravity: In untreated or poorly controlled diabetes insipidus, urine specific gravity remains low due to inability to concentrate urine. A persistently low urine specific gravity is not an acute adverse reaction that requires immediate reporting. B. Polyuria: Excessive urine output is a primary symptom of DI before treatment. Continued high urine output may suggest inadequate dosing or nonresponse but is not considered an urgent side effect needing immediate provider notification. C. Polydipsia: Extreme thirst is common in DI and typically improves once vasopressin takes effect. If polydipsia persists, it may point to suboptimal therapeutic response rather than an emergent adverse reaction. It warrants follow-up but is not a critical side effect. D. Worsening headache: Severe or worsening headache while on vasopressin may indicate water intoxication and possible hyponatremia from excessive antidiuretic effect. This can lead to cerebral edema, which is potentially life-threatening. Prompt notification to the healthcare provider is necessary to prevent neurological complications.