How could you possibly know this?
Oxycodone can and does damage the liver, even if it's not that severe. If he has been dosing for very long periods of time at 200mg+, he could very well have endured liver damage.
He could also have a lower/higher concentration of the enzymes that metabolize oxycodone which has been known to cause toxicity.
Oxycodone has also been linked to increased liver toxicity in patients with previous liver problems and users with Hepatitis C. If he is injecting, he could have Hep C which could be the culprit. He didn't give much information.
I think you are totally misreading what the quote you posted is saying. Oxycodone itself does not cause liver damage. If you metabolize oxy slowly it can build up a toxicity of the oxy in your body. What this means is you will have more oxy in your body/blood/system than a person on average would. Therefore you will be more likely to OD because it dissipates so much more slowly. If your liver is already compromised by some type of liver disease such as Hep C then you are going to metabolize the oxy and any other drug in the world that is metabolized by the liver much more slowly causing an more than average persons buildup of the drug in your body in general (not the liver) which increases the chances of the same types of problems you would have when you take too much. This is why all drugs that are metabolized by the liver caution that in impaired liver function (such as Hep C) lower doses than normal are recommended. This is because your liver does not process it (clean it out of your body) as quickly as it should
causing increased levels which lead to toxicity!
The whole point I am trying to get across to you is oxycodone does not cause liver damage, but liver damage will cause the oxy to not be processed (metabolized) out of your body as quickly as it should which could lead to a build up of oxy to toxic levels.
*edit*
OP, long term high dosages of oxycodone can cause problems no doubt. The main problems include slowing down of the digestive system which most commonly causes constipation. Please dont think that this is insignificant though. I have taken care of several patients who had 'had a little constipation'' that ended in a blockage in the intestine which led to a rupture which is a medical emergency requiring surgery ASAP and can lead to infection and death. It can also cause an increase in pain(usually chronic pain patients) in rare instances that can only be relieved by stopping the meds (oxy).
In studies of long term use of any narcotics for pain, some results show that it can mess with your immune system slightly and your levels of testosterone. People taking pain medications should have their levels checked periodically. Again, these 2 findings are a little controversial and do not usually significantly impact people.
So the really big issues regarding taking oxy are the ones most people know about. This is the decreased respiratory drive in higher doses. This is what kills you in an OD. Of course if it doesnt kill you it could cause permanent brain damage due to decreased oxygen getting to your brain during a respiratory arrest if you are not oxygenated quickly enough. But the most common and biggest issue is addiction and tolerance.
You have a lot of contradicting info in this post and some of your prior posts. You imply you only take it when you can get it but then on one post you stated you had a prescription for oxy 30mg. you state in some places that you only take occasionally but yet you have a tolerance of over 200mg. Im not trying to call you out just want to warn you that a full blown addiction/tolerance/dependence on oxy is not fun. If you are not there yet, then my advice would be stop while you are ahead. Use it recreationally and on occasion. But trust me, as a nurse for 20 years and as a chronic pain patient with a long term dependence on oxycodone, it quits being fun when you have to have it, everyday, all day.