The narcotic stuff is for using when and while you need it. If there's some left lock it away, you may need some later. When it's over you can keep it locked away for the next time (and there will, unfortunately, be a next time) or drop it off at the local Walgreen's or cop shop for safe disposal. As my dear old seanmathair used to say, "Chomh luath agus in féidir."