Naggers
Bluelighter
Personally, years ago I attempted to achieve a central narcotic effect from loperamide, and with many attempts at dose in concert with many compounds (p.o. quinidine, omeprazole, etc, etc).
End result after various idiotic attempts: Yes, some central activity when induced with a combination of agents I cannot recommend (the barrier is there for a reason), but of a very "dirty" nature (like meperidine, but even 'dirtier' and far less 'enjoyable'; certainly not worth the exposure risks of the facilitating agents, not to mention the worrisome toxicological unknowns).
Point: Even when introduced centrally, the drug is inherently shitty, and (again) a potential toxicological nightmare.........
Same, felt very unhealthy. As much as I love opiates I wouldn't try it again.
I haven't tried piperine for PGP inhibition, but there are 2 or 3 good long threads discussing it as a possible potentiator of codeine one Drugs-Forum and BL (sorry, too lazy to google right now. They're in the first few results so easy to find). Last time I checked them nobody could find any definitive answer on CYP2D6/CYP3A4 potentiation/inhibition, however somebody found the average piperine content of black pepper, and also found a study of it's effect on frogs or something like that, so he came up with an amount of black pepper which is likely to give an effect, but it was more likely to fuck up your GI tract before any worthwhile potentiation. IIRC a couple of posters tried it and found this out the hard way. Sorry for being lazy guys after you've all posted such interesting links, don't think I could even get up to take a leak right now.