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 does not indicate tolerance; tolerance refers to reduced effectiveness of the medication over time, not an adverse effect. B. While anxiety can cause headaches, in this context, the headache is a known pharmacologic effect of nitroglycerin due to vasodilation. C. A headache is not a sign of allergy to nitroglycerin; allergic reactions would involve symptoms like rash, swelling, or difficulty breathing. D. Headache is a common adverse effect of nitroglycerin caused by cerebral vasodilation. It is usually mild to moderate and often decreases in frequency or intensity as the client continues therapy. Providing reassurance and education about this expected side effect is appropriate.