Naproxen expires on the expiration date printed on the bottle, which is the final day that the manufacturer guarantees the medication's effectiveness and safety, notes Drugs.com. Outdated naproxen should be discarded properly, according to MedlinePlus.
Some medications used for minor health problems are generally safe to take past their expiration date although they may not be as effective, states Drugs.com. If the expired medication is taken and has no therapeutic effect, it is best to discard it. Medications used for chronic or life-threatening health problems or that appear cloudy or degraded should be replaced. Insulin, EpiPen, eye drops and injectable medications are not recommended for use after their expiration dates because they degrade quickly once they reach their expiration dates.