Nitroglycerin can get old. And when it is old, it may not work. If your nitroglycerin supply is past its expiration date, get a new prescription as soon as possible. Keep your nitroglycerin in the container it came in and tightly closed. Do not open your sublingual nitroglycerin until you need a dose. Replace your tablets every 3 to 6 months. A nitroglycerin spray may last up to 2 years before it expires. You may get a headache when you use nitroglycerin. Or you may feel burning or tingling under your tongue with nitroglycerin that is used under the tongue. But if you don't have a headache or feel burning or tingling under your tongue, it does not mean the medicine is not working.