Short answer: It might be possible, but with mirtazapine and Elvanse you should only consider a psilocybin session after discussing it with your own doctor. I cannot verify your specific situation.
Mirtazapine may reduce or even blunt the psychedelic effects for some people. In practice, options like a supervised taper or a medically guided switch are sometimes considered, but never change or stop medication without your prescriber’s approval.
Elvanse (lisdexamfetamine) typically does not block the psychedelic effect, yet it can increase heart rate and mental activation. Some facilitators suggest skipping the dose on the day of a session only if your clinician confirms it is safe for you.
If you are exploring this in the context of trauma work, you can read more about PTSD therapy here: PTSD therapy.
Hope this helps you plan a safe next step with your clinician.