Corpus Callosum might be able to give you some better medical feedback on this but, cant you, for the sake of safety, skip changa and smoke freebase dmt instead?
Edit: Simple wikipedia check turns this up:
The potential for dangerous drug interactions with mirtazapine is considered to be very low, if not completely negligible. As a serotonin receptor antagonist, mirtazapine will not cause serotonin syndrome at any dose, nor is it capable of causing tyramine-induced hypertensive crisis, unlike the SSRIs and MAOIs, respectively. In fact, mirtazapine can actually be used to treat serotonin syndrome.[49] However, mirtazapine is said to be an indirect agonist of the 5-HT1A receptor, which can contribute to serotonin syndrome when combined with other serotonergic drugs.[50]
Kind of weird though, because the last sentence seems in direct contradiction with what is said before.. I would avoid it just in case. Lets see of Corpus Callosum can give his feedback here..