Well, there is definitely literature out there that supports cimetidine (Tagament) inhibition. It inhibits the CYP3A4 which is an enzyme that is responsible for the oxycodone -> noroxycodone (which has no opioid receptor affinity). I'm not sure how it affects peak plasma concentrations, time to peak plasma concentration or half life. From my experience it seems to make the high last longer, but not as intense. This has also spurred my to do more research into various inhibitors.
A bit off topic, but, I just read a paper on Grapefruit juice administration to patients receiving 10mg Oxycodone and they took blood samples. They found it significantly inhibited the CYP3A4 metabolism and increase plasma concentrations and prolonged the halflife of oxycodone. It's also important to note that patients took 200ml of grapefruit juice (they didn't specify white/red) three times a day. On day 4 they took the 10mg oxycodone. The authors posit a lot of inhibition is happening in the GI tract before being transported via the portal vein to the liver. It opened my eyes to think there are cytochrome enzymes in the small intestine that start metabolizing drugs before the liver. The study also found elevated levels of oxymorphone and noroxymorphone from metabolism by CYP2D6.
I actually enjoy the grapefruit juice. I squeeze it fresh each time!
Anyways, hope that helps!