If you are addicted to vicodin or oxycontin, will you always have withdrawals when you stop taking it?

Someone I know has been addicted to vicodin and oxycontin. But now he says he no longer takes it, but I have not seen any type of withdrawals. Is this possible?

: http://alcoholdrugstreatment.info/if-you-are-addicted-to-vicodin-or-oxycontin-will-you-always-have-withdrawals-when-you-stop-taking-it