not sure how to add the kappa3-opioid receptor modulation, probably a PAM for the kappa3 receptor. It is discussed in the below paper;
Schreiber, S., Rigai, T., Katz, Y., & Pick, C. G. (2002). The antinociceptive effect of mirtazapine in mice is mediated through serotonergic, noradrenergic and opioid mechanisms. Brain research bulletin, 58(6), 601-605.
This may also be why there are withdrawals from mirtazapine, as the opioid system is not modulated when cessation of mirtazapine occurs.
I can't change it but the threshold doseage is wrong. This drug is prescribed down to 15mg and has sedative effects at that dosage.