I have noticed this as well, and like the guy above I have not had a major case of the flu or anything worse than a mild cold since I picked up the habit. My bowels also work better if I am not on high/regular doses of an opiate. I can even eat ice cream if I take 5mg of oxycodone, if I even try to eat that stuff without an opiate I am in the bathroom within 20 minutes sshitting water.
I am mostly clean now and still going strong on the not catching the flu end.
Interesting thing to note is sneezing and runny nose were some of the first w/d symptoms I would have back durring heavy use and detox. Those would always clear up as soon as the oxycodone kicked in.
The downside is they can mask problems. I found lots of minor aches and pains were waiting on me when I detoxed. I assumed they were just part of w/d and some were, but others were not and required some treatment. For example one of my knees was in horrible shape for my age, and while I knew it was in bad shape before and while using I could not feel it most of the time so I was working on a bad knee that needed rest and did not even realize it. So now it is worse off than it should be and at some point I am going to have to have the joint replaced.
I am not saying that would not have happened anyway but I think if I could have felt the real pain level durring the years I was addicted to oxycodone I might have stayed off it more and gotten a few more good years out of it.
Addiction is the main concern of course, but opiates can cause other health problems too. Just keep an eye on yourself when you can, I know I wish I would have done so more often.