Addiction doesn't always happen because someone is abusing drugs. Patients may be using their drugs as prescribed, but if they have chronic pain issue and have to be on those drugs for a long period of time, their body becomes used to having that drug in their system. They can build up a tolerance and require a higher dose just to get relief from their genuine pain.
Once they realize they are addicted, the nightmare begins for them. They don't want to be addicted but since they have genuine pain issues, they need the drugs to be able to function. They need to be able to control the pain so that they can work, take care of their family and carry on in their life.
So they have a huge dilemma and are probably quite ashamed as well. The genuinely need the pain meds but they also realize that their drug use is becoming a serious problem. They do not wish to live a life on chronic pain, nor do they want to be an addict. They may have an image to maintain, lead a respectable life and have a background where they have always been anti-drug. Yet here they are - addicted to pain meds.
This is a real problem in the world of opioid addiction and one that needs professional help to be dealt with, both for the addiction and for the chronic pain issues. help is available but you have to admit the problem first.