If the opioid like vicodin is used long term it becomes a "physical" dependency because the body will change and adapt to the presence of the medication. If someone who is addicted stops using the opioid they suffer withdrawal which often is far worse than the original pain. Simpy put, if your about to undergo surgery and your surgeon is an opioid addict the last thing you want is for the surgeon the night before say to himself-I think I will quit in the morning so I will be ready for the surgery. You WANT him to take those pills before he cuts into you. Then afterwards he can begin the healing-if he can.