Something I've been doing in the past couple of days may prove useful for my U.S. audience that has access to legal kratom. A vendor suggested to me that mixing "stem & vein" kratom with your favorite variety of regular kratom would make the whole effect more powerful -- and this seems to be true in my experience. The combined effect is more satisfying and complete. It also seems to last longer.
We know the blend of alkaloids is different in stem & vein, even when taken from the same leaf, same tree. Most people only use Stem & Vein when trying to lower their tolerance to the pure kratom leaf powder, which generally has more of the effect we want, so I doubt most kratom consumers have tried mixing about 2/3 regular kratom with 1/3 stem & vein kratom. I never had, certainly.
The reason why this mixture's effects were a shock to me is that most Stem & Vein, by itself, seems less satisfying and a weak version of the usual "higher-octane" variety.
Stem & Vein is fairly hard to find. Many vendor don't even carry it on a regular basis. Many of those who do carry it don't grind it up to the same super-fine powder that is commonly available with other strains, but the one I'm using did (this may help absorption).
In any case, I'd suggest you try this and let me know how you like it. See how it works for you.
It is a shame we don't have more factual research available to tell us how kratom does the amazing things it does, but that's just the current state of affairs. Most research seems to be chosen and designed to confirm the bias of the organization or agency that funds it. One research group doing exciting work in demonstrating the radical positive differences between kratom and the opioid compounds is the team led by Dr. Andrew Kruegel at Columbia University. They deserve our support.