....cannabis is the BEST potentiator, at least for me. It also seems (is) a much safer combination of drugs....
I'd agree with this - there's no drug interactions on a pharmacological level. So other then potentiating by way of being "depressants" (although tbh I don't think you'd really call cannabis a depressant!), I would say it's safe.
Imo (and I'm going just on personal experience and cannabis would be my least DOC) I reckon any potentiating effects would be due to the way THC/cannabis(noids) seem to enhance what one is feeling - ya feel like ya nodding and euphoric, it'll enhance it.
Thoughts?
Best opiate potentiator I've ever tried would be Tramadol! (second being DXM and excluding other opiates [yeah I know
is an opioid, but I'm not counting that since I've found Tramadol's analgesic efficacy to be terrible]

).
Most of the other suggestions are (I've found) generally rather weak CYP450 (specifically CYP2D6 being the most active enzyme) effectors (obviously generalising here. referring to the most common opiates & their metabolisers - codeine, oxycodone, morphine, etc

)
.....adding white grapefruit juice to that would actually help. Cimetidine doesn't do it all by itself. I'd have to look up the specifics, but GP juice hits the CYP450 harder IIRC and cimetidine hits both GABA-A & B more efficiently....
Umm, not quite for either actually
Firstly the Grape Fruit juice, even on BL you'll get many varying opinions as to whether this works. True the theory goes that it is broken down via the CYP450 pathway - to what extent or even whether this is 100% is (afaik from papers/forums/people I've read) still very much up for debate! Secondly, CYP2D6 nor Grape Fruit Juice touches in anyway GABA.
With Cimetidine, clearly depending on how indepth you want to go, but as a drug it actually has a few MOA - predominately being an antihistamine (specifically an H2-receptor antagonist) - however since it does have other MOA/effects it is used (off-label of course lol) for other treatments.