agree with both above. kava will likely mute the effects of microdosing psilocybin if taken too close together. if your microdose is morning, then late afternoon and evening kava shells should be ok from interfering with the other. similar if you microdose before bed, avoid kava for the evening is my recommendation.
as for bad effects, even though everyone is different, I've not had any issue having kava while under influence of large and huge dose sessions. heavies and balanced kavas did work with me better than the one heady tried which was quite overwhelming... for sure it can be quite a different and intensified experience as with adding cannabis to one or both... also to say, if microdosing, only negative effect I'd assume is the kava cancelling the subtle effect of less than half a gram of GTs~