Just learned that mitragynine
indeed seems to be a D2 antagonist, among others. Unfortunately, cause I hoped to some day extract a more pure kratom. Interestingly it only feels like an antipsychotic in the presence of another dopaminergic, like memantine which is a D2 agonist, but when used as the sole drug, kratom doesn't share that nasty signature. Still, it feels somewhat 'locked-down' to me in terms of euphoria, but too I happen to be very sensitive to this sort of stuff.
@JackARoe: All these strains differ so widely that anything's possible. I've had a red vein strain which put me straight to nod when my tolerance was much higher than now, and from just one spoon of material. Was a sample pack, so quickly used up and re-ordered but got bunk stuff. This now is more like a cleaner coffee - usable on its own but barely touches withdrawal symptoms. The shit they sell in NL smartshops just eats a hole in your wallet but was next to inactive. We deal with more than 30 active alkaloids (though many of them probably in low to very low concentration)..