I've only ever dealt with Kanna in 300x-500x concentrates, so I'll be speaking on this realm of super heady concentrates in my response here, just a heads up.
I've mixed it with a handful of psychedelics, but mixing it with MDMA left me grinding my teeth damn near flat, unable to form meaningful thoughts, pouring sweat for quite a while. I suspect that I was approaching a terribly dangerous point of serotonin syndrome but I couldn't tell tbh. I just rode it out and ended up being fine, at least from my own perspective. Mixing Kanna with psychedelics (specifically that lack MAOI and monoamine releasing properties) has been nice, often adding a pleasant stimulation and sometimes seemingly potentiating the effects of mushrooms, 2C-B, and LSD, but only very mildly.
Taking half a gram of ~400x Kanna extract put me in what I can only refer to as a damn near psychotic roll of pure rage and emotionality. A former best friend had emotionally led me on for months, only later admitting that he just uses gay men for sex when he's bored. That roll made it very difficult not to act towards him with extreme violence. All five of the people I was living with were absolutely terrified of my behavior towards all of them too, as recently a local spice addict (we colloquially referred to them as spice zombies) had fallen through my window late at night in what seemed like a breaking and entering attempt. My trusty pocket knife and I handled this situation, solo, because each and every one of them were too bitchmade to even peeek into my bedroom (door was both open and unlocked), and after me screaming at them to get in there, they decided instead to stay locked in their rooms out of fear.
If MDMA, MDA and 6-APB (the other three empathogens I've used excluding oxytocin which is like an empathogenic whippet) allow your emotions to come out like a controlled release from a series of dams with gates on levers that you can precisely control as far as the outwards flow of emotionality, Kanna is instead just exploding every single damn and letting them flow out completely uncontrollably. I was pacing around my living room for literally hours, screaming every feeling I'd had and felt that I didn't think would be right to have communicated at past points, it was like an explosion of built up tension. The eugeroic effects were interesting too, two drinking glasses got accidentally chipped on the sink just trying to fill them up (I was shaking like crazy) and a plastic cup literally exploded in my hands from an accidental overexertion of force. I also put my hands on the edge of a wooden coffetable and it bent, I had to bend it back and apply polyurethane and then spray lacquer to get it normal again.
