I'm concerned reading your response. You said you feel normal on drugs and ruin everything when not, or something to that effect. This changes the picture quite a bit. The idea that taking this drug might be in some way related to therapeutic work (though all of this is all experimental) is now surrounded by the issue of taking drugs in general to "feel normal." That seems like it is a potential problem that needs to be addressed or at least considered.

Other things also seem to make the idea very risky. That you have a complicated relations to psych meds, both addicted and rejecting. That you have PTSD. What if you have a bad trip? and traumatic stuff comes up? and there you are, with session over, but still high for hours without any help? You could be re-traumatized and thereby harming yourself, which a therapist has a duty to try to keep you from. On that topic, that you said you feared losing your therapist and that when it happened before you had a breakdown. These are many red flags and risks, substantial ones.