Tollerance could be your issue. The more you use, the more you’ll need next time, that’s without a long enough break.
I was on mirtaz at a time and felt it enhanced the sedation of opiates. I was addicted to opiates at the time too.
I used to get high on codiene from the morn. Take mirtaz about an hour before bed.
What doses are are you talking about, how long have you taken codeine recreationally, how often and when did you start your mirtaz?
Do you use any potentiators to boost your codiene hit?