Assuming that you're talking about fake OxyContin 80mg pills...
Could be anything, read the other thread. There is also a distinct possibility that there isn't anything in them at all.
I've read the other thread, there is (was?, I dunno if they're still available) an issue of the DEA microgram that mentioned fake '80s contained fentanyl, which would explain why your buddy got an opiate high off them. However, fentanyl and oxycodone are very different opiates and fentanyl is downright dangerous if not taken extremely carefully.
We can't tell you what's in your friend's (possibly) fake pill. When in doubt, flush 'em down the toilet.