A nurse in the emergency department is caring for a client who took 3 nitroglycerin tablets sublingually for chest pain. The client reports relief from the chest pain but now he is experiencing a headache. Which of the following statements should the nurse make?

A. "A headache is an expected adverse effect of the medication." – Nitroglycerin is a vasodilator, and headache is a common and expected side effect due to cerebral vessel dilation. B. "A headache is likely due to the anxiety about the chest pain." – While anxiety can cause headaches, in this case, the timing and use of nitroglycerin point to the medication as the cause. C. "A headache is an indication of an allergy to the medication.” – Headaches are not a sign of an allergic reaction to nitroglycerin. Allergic symptoms would include rash, itching, or breathing difficulty. D. "A headache indicates tolerance to the medication." – Tolerance to nitroglycerin usually develops over time with frequent use, and it typically reduces the therapeutic effect, not causes headaches.