Sublingual nitroglycerin tablets should be discarded six months after opening.
Past tradition has led pharmacists to counsel patients on the "instability" of sublingual nitroglycerin (Nitrostat, NitroQuick, NitroTab).
It's true that older formulations lost their potency when repeatedly exposed to light, air, and moisture.
But today's formulations are more stable. If stored properly, they are good until the expiration date on the bottle...EVEN IF OPENED.