Havent read all the replies so apologies if this has already been mentioned:
You asked about Kratom potentiators:
One way to potentiate is with piperine, aka black pepper extract. It actually enhances the effect of many sedatives and increases nutrient absorption in the gut. It makes the otherwise useless curcumin (turmeric extract) actually worth a damn for example. You dont need to take a dose of piperine that actually has much of a physiological effect to get the absorption benefits. People take it medicinally sometimes in the range of grams but it can be a double edged sword for this. All you need to potentiate curcumin according to science is 20mg. I take 50mg with my kratom for good measure. Theres a world of difference IME. Extremely handy for getting the benefits you need from a lower dose fo kratom without picking up all the shitty off-target and side-effects that pushing the dose has. BPE is very cheap if youre only using it for absorption i got a bag of 25g powder off of amazon for £25. You can get caps too i believe but they might be for people dosing higher, and if youre chugging the krat you want the powder to be in there with it IMO not hitting later, it needs to be present in the gut with the nutrient not just affecting you when you consume the nutrient. More often than not curcumin comes in caps with BioPerine in the dose youd need to increase your kratom effects, and curcumin itself can potentiate analgesics, and aside from also being a great anti inflammatory, id postulate that since its good for liver conditions itd alleviate some of the strain the kratom puts on it.
Also things that enhance nitrous oxide pathways / increase production of NO like agmatine can increase the effects of kratom without ramping up your tolerance as you can get the desired effects from a lower threshold.
If youre into being a guinea pig then BPC-157 lowers tolerance to drugs across the board, kratom included. But thats like, mostly only tested in rat models and we dont know what all the issues are with it yet. Theres no such thing as a free lunch in biology and bpc157 suspiciously looks like one. It seems that it attenuated rats response to morphine induced analgesia though so thats the possible offset. It had a similar effect with amphetamine but i only saw it as a positive, it lowered tolerance while reducing the head twitch response and other compulsive stimulant induced physical manifestations, which can sometimes infer less efficacy but seems to actually have just alleviated the shitty physicals whilst not affecting the cognitive enhancement.
I had a recent flirt with Kratom myself. It ended badly as I am extremely intolerant to virtually all herbs and remedies and I got myself addicted in just four weeks and had to stop cold turkey in a terrible health condition I did get some really nasty withdrawals to suffer.
But I did enjoy the effects of the kratom while I was taking it and I was particularly interested in this science of potentiators. Black pepper I have been using for a long time in combination with my cannabis edibles because the pipperine in the pepper slows down the degradation of the cannabinoids inside to receptors and makes for a much stronger and longer lasting effect from cannabis.
But I also have been combining my cannabis edibles with sunflower lecithin which I believe is I'm very useful potentiating as well.
Turmeric is also said to be a strong potential for kratom and of course as you have expressed is much more medicinally active and usable when combined with black pepper or the extract.
In all my years of experience however, with psychoactive substances, diet and supplements, there is one particular food which I find to be the most powerful potentiation of all psychoactive substances I have ever experienced literally doubling the effect of my cannabis or more.
Raw organic garlic. Must be crushed first and left or 10-minutes but the Allicin to form. Honest to God I have always noticed a significantly stronger effect from any psychoactive substance if I have consumed raw garlic especially if it is on an empty stomach away from food.
3 crushed cloves swallowed raw, at least doubles the intensity of the effects I get from my daily cannabis edibles and vaporization.
I first noticed this correlation very strongly years ago with ketamine use if I had consumed war garlic with my dinner then I would be in a k hole on a tiny line every time and really floored by it.
I also definitely noticed potentiation of the kratom with the raw garlic. I was particularly enjoying the Kratom/ cannabis edible combination, I was taking them together with the raw garlic, black pepper and lecitihin.
I also take oil or oregano daily, I believe this mate also have a general potentiating action.