Does flonase become toxic after it's expiration date?

Just weaker: Futicasone (flonase) and all other medications lose potency over time. They don't became toxic or poisonous. Fda regulations state that the time after manufacturing when a drug has lost 10% of its original potency be designated its expiration diet. That means that on that date the drug is still at 90% of its maximal strength. It won't hurt you to use it but it might not work as well.