Final answer:
The nurse should inform the client to prepare for the most common side effect of headache when taking sublingual nitroglycerin.
Step-by-step explanation:
The nurse should inform the client to prepare for the most common side effect of headache when taking sublingual nitroglycerin. Sublingual nitroglycerin is a medication used to relieve chest pain or angina by dilating the blood vessels and improving blood flow to the heart. Headache is a known side effect of this medication due to its vasodilating effects.