Toz
Bluelighter
You are nearly on the money with this one - great-fruit juice, Tagamet, and a host of other compounds and plant extracts inhibit the drug metabolizing drug CYP3A4 - however the more potent O-desmethyl tramadol is the product of CYP2D6 activity. I cant even remember a potent CYP2D6 inhibitor off the top of my head - a rule of thumb is that many opioid drugs are metabolized by CYP2D6. I believe the only way to achieve this end goal is in individuals with high atypical CYP2D6 activity - my girlfriend is one such person - she took a single T3 (co-codamol 30/500) for her period - vomiting, pin-prick pupils - not having a good time and displaying high dose opioid use symptoms. Codeine is a pro-drug and is metabolized by CYP2D6 to morphine.
Quinidine is a strong CYP2D6 inhibitor and probably what people would use for this kind of thing, I think.