Consequences result as the body seeks a balance and compensates for the increased dopamine and increased pleasure. Tolerance develops when the body compensates and the individual soon needs more and more OxyContin to get the same pleasurable feelings that one or two doses used to provide.
OxyContin addiction creeps up on the individual until acquiring the drug becomes a full time obsession affecting friends, family, career, kids, finances and possibly involving the police.
Most people who suffer from chronic pain do not experience a high or buzz when taking narcotic pain medication as prescribed. As a matter of fact, it tends to energize you because pain wears you down and zaps your energy. When a chronic pain sufferer experiences pain relief they are able to do more because the pain is supressed.
The problem is that the body builds up a tolerance to the medication and then you need more to achieve the desired effect - not a high - just relief.
Of course some people do take the drug in order to experience a high but I don't think that this is what Rush was doing. He started out like many with a legitimate need for pain relief. People are not aware of the addictive nature of this drug until it is too late. If you have never been addicted to anything before you have no reason to think that you will get hooked.
It happened to me and I believe that this is what happened to Rush. Incidently, it happens to a lot of people.