What IS Psychedelic Tolerance, chemically?

[tryp2fun]

I'd like to know whether using 5-HT antagonists causes 5-HT upregulation, and if this provides means for reseting psychedelic tolerance or potentiating psychedelics. One of my friends has used mirtazapine and before we trip together he ceases to use it for a couple of days. He tends to get more high from similar amounts of psychedelics than the rest of us. Might this be an example of 5-HT antagonist inspired upregulation?

An antagonist binds to a receptor but causes no effect on receptor activity, by definition. Thus, it seems hard to imagine a mechanism by which an antagonist can reverse tolerance in the absence of an agonist. An antagonist should be able to inhibit tolerance in the presence of an agonist, but at the expense of the agonist activity. However, an inverse agonist could theoretically reverse tolerance, since an inverse agonist reduces basal receptor activity.