A nurse administered nitroglycerin sublingually to a client who has angina pectoris and experienced chest pain. The client states that his chest pain is relieved but now he has a headache. Which of the following responses by the nurse is appropriate?

A. "A headache is a common adverse effect of this medication, but it will probably occur less often over time." Headaches are a common side effect of nitroglycerin due to vasodilation, and they often diminish with continued use. B. "It sounds as if you are allergic to this medication." Headaches are a known side effect, not necessarily an allergic reaction. C. "Your headache is probably a result of anxiety about the chest pain." While anxiety can cause headaches, in this context, it is more likely due to the medication. D. "A headache indicates tolerance to the medication." A headache does not indicate tolerance; rather, it is a common side effect of nitroglycerin.