^unless you're prepared to call the emts at the time of ingestion, as tricomb already suggested.
so yea, if this person has no other drugs in their system, they could probably get away with eating 2.5mg of this prep of oxymorphone.
BUT, if they have ingested anything else, especially is it was a cns depressant (half a bar of xanax, a beer, half a drink - I mean ANY amount of ANY cns depressant), taking oxymorphone without a tolerance to the drug and knowing how it will actually affect you, well, this is like playing russian roulette. Actually probably even worse odds than russian roulette...
wellbutrin shouldn't cause any problems. 1-2mgs and you'll/who ever it is who is taking it will probably be fine. key word is probably.
stay safe, and enjoy.
frankly there is a good chance who ever is taking this will be able to take more than 2mg and be fine, although super fucking high. but it's not worth taking a lot all at once and then finding it is going to kill you. thus, start slow, if you're never done it before, and work your way up, slowly. the only real way to guarantee you'll be safe and have as much fun as possible.