I find kratom to be a very benign substance compared with just about anything but cannibis and benzos as far as interactions go. I prefer it to traditional analgesics like morphine and pethidine and even fentanyl derivatives.
I get all the beneficial analgesia with only pupillary constriction and occasional blurred vision when combining it with alprazolam. No nausea, no itching, and best if all no issues with constipation as long as I drink enough water and eat eat a fiber supplement each day I take it, starting the night before I go on occasional extended period due to the difficulty in obtaining painkillers legitimately because all the docs are so fucking paranoid these days.
I've had excellent results combining kratom with:
-allylescaline
-4-aco-dmt
-DPT
-Kratom has a special synergy with Tricho cacti
-A. Muscaria
-HBWR
-DXM
-glaucine HBr
-Any number of (mostly) mild botanicals
-Dagga, Blue lotus, Kanna, S. Nemororsa, H. Salicfolia, etc
-Many pharmaceuticals: traditional analgesics, amphetamines, benzos, zyprexa, bupropion, Mirtazapine, etc.
The only actual negative interaction was when smoking DMT freebase extracted from M. Hostilis and mixed with powdered B. Capii alkaloid extract and B. Capii leaf (I believe "changa" is the slang term for this type of preparation in modern vernacular) for easier smokability from a bong.
I had taken 12g of Bali leaf about 45 minutes prior and was definitely feeling it) and after a bowl of sour diesel then got the ingenious idea to take a few puffs of the changa as I was in a good headspace. I only got in one solid hit before the normally beautiful susseration that accompanies the onset of smoked DMT was instead a horrible ringing in my ears and sudden, severe nausea. The visuals were more akin to the "brain movies" of Shulgin fame of traumatic childhood memories, a pervasive sense of being poisoned and overheated for over an hour. No catharsis or insight was possible in this negative headspace. Thely positive result of this experience is I know NEVER to do it again. The experience was very similar to the description of 5-meo-DET in Tihkal with a longer duration.