It depends on the medication, and how the dose is formulated. It can be 4, 6, 8, 12 or more hours. It's a frustrating answer, I know, but the true answer - without specific info on the particular...
yes if it in 500 milligrams form and take two gets you feeling good no pain also helps with coughing and its narcotic you only getting threw a doctor or a good street pharmacist lol