Pretty much every pill-form drug is good for at least 2 years at room temperature, tightly closed and protected from light and moisture. The guideline is 90% potency; the drug will lose potency at a different rate depending on what else is in the pill. You 2.5 year old Drontal should be fine! Aspirin has a smaller shelf-life because the actual molecule breaks down quite easily; I'm sure you've all smelled vinegar in an old aspirin bottle!