For the record - if you read this entire thread you'll see conflicting info like: Grapefruit juice for morphine or Codeine, Pepcid AC for Oxy etc. Then you'll see those two recipes reversed 4 threads down along with info saying if you take grapefruit juice withHydrocodone it will be inactivated.
I don't know about all this personally so I'm going to dabble a little with quinine, grapefruit juice, and Tagamet. That being said, I'm a moderate user of vikes, percs, and Tylenol 4, usually use all day 3-4 days a week or so. I wouldn't try ANY of this shit (or anything that even 1 poster said would potentially inactivate) if you are someone who gets power pills (Oxys, morphine, dilaudid, roxies etc.) at a semi-infrequent rate. I.e. if you do a 40mg Oxy once a month as a big thrill, don't risk fucking up your buzz.
I can say without exception: DO NOT attempt to "potentiate" normal beans, I.e. Vikes/Percs/Codeine with Benadryl (diphenhydramine). If you find someone who has 0 opiate tolerance and feed them two Benadryl you'll see why. Benadryl is (for most, but not all) people FAR stronger of a drug than mild painkillers cut with acetaminophen.
In other words, only use Benadryl on a buzz that has no risk of being overshadowed by it. The exception to this is if you're not really an opiophile and you just want to get faced. In this case just pop 5 Benadryl and leave the poor defenseless 10mg Oxycodone out of it =-)
I know nothing about Herion etc, but my guess would be that diphenhydramine could be a nice complement to it, having consumed 10 Benadryl for kicks one time.
I'm a purist when it comes to opiates, I would say it's sacrilige to pop any type of benzo if I have any kind of noticeable bean buzz going. I think of a potentiator as a normally inactive, mundane substance that has some kind of chemical action in the body to boost the quality or duration of a given opiate buzz.
In the course of writing this I ingested 12oz. Of white grapefruit and a Tylenol 4 (60 mg Codeine). There may be some potentiation going but I'll definitely drink more to be sure next time. I do think it's highly unlikely that the Codeine was rendered inactive as one person suggested.
Finally, and I can't believe that nobody mentioned this (in the 6 pages of the thread I've read) the two biggest potentiators I've ever come across are: FOOD and CAFFEINE. Food specifically used while on generic percocets, maybe 2.5 hours in as the buzz is starting to wane - boom! There it is again. Ok food is necessary for life, maybe it doesn't fit my very own description for a potentiator, but it works! A large hot coffee also works wonders, as does a large iced coffee.
To sum - don't use a stronger substance than the one you're trying to potentiate because you're just overshadowing the buzz usually.
If your bean supply is short and those 1-2 pills are all you're liable to get for a while don't fuck it up by ingesting something that could inactivate some of the goodies floating around in your body =-)
Use a process of trial and error to find out what works best for you and your body chemistry/tolerance!
****EDIT****
In the last few days i've taken Codeine (Tylenol 4) with Grapefruit Juice and then Cimetidine (Tagamet HB) with Morphine (Poppyseed Tea). Drinking Grapefruit Juice for Codeine seemed to draw the buzz out and make it last a little longer, but it definitely didn't heighten the feeling for me (though i did a really low dose of 60mg).
Taking 800mg of Cimetidine on the other hand really kicked the seed tea buzz into overdrive! However i do wonder now about the RISKS associated with potentiating opiates. I know that these things are not "Contraindicated" for use with opiates (i.e. really fucking bad to combine), but i hear rumblings that it's a really bad idea to be personally tweaking the enzymes of stuff in your body. Anyone have a rough idea of JUST how bad?