First a can of tinned grapefruit, in GF juice. I LOVE tinned grapefruit, the white kind more so than the red.
And there is a rather nice little bonus of sorts resulting from its consumption. There are several flavonoid compounds within grapefruit that act as reasonably strong inhibitors (or substrates, not sure which
of hepatic cytochrome P450 pathways 3A4 and 2D6, these happen to be the main enzymatic modes of metabolic destruction where morphine is concerned, means I usually take my oxy first, as oxycodone is a prodrug, in part at least alhough not afaik an obligate one as is say codeine. Oxycodone gets metabolized to a proportion of the far more potent oxymorphone (one of those uncommon opiates that has a real cracker of a reputation for being one of the most enjoyable opioids of all, via IV route.
Not even remotely likely I'd succeed in getting my oxycodone changed to the morphone (that is, by any of my doctors who work at the practice I frequent), bugger all chance is more like it.
I would have either to find someone who had some and who is willing to part with any in trade, or work out a synthesis of OM from oxycodone.