Thought this was really interesting, seems like its saying that downregulation of 5ht2a receptors are long term...
Edit: Realizing that I think they mean while still on the antagonists. Although I do want to state that there may be unknown variables in the premise of downregulation/upregulation that may have not been fully explored yet. Maybe there are permanent changes that can possibly occur.
Its extremely interesting as well, that, as I think I have brought up before, that schizo/OCD/and other conditions appear to be linked to 5ht2a receptor dysfunction, which alternatively I suppose may also be the case with HPPD. If I remember correctly there is consistency with HPPD and previous mental health conditions of the same lines. Even I personally have had mild OCD.
It is strange as they state as well that the antagonist induce downregulation, instead of upregulation, which is quite paradoxical as they state.
Functional regulation of 5-HT2A
The functional regulation of 5-HT2A involves desensitization and re-sensitization, which differentiates 5-HT2A from conventional GCPRs (e.g. the B2 adrenergic receptor) and prevents overstimulation.1 At the molecular level, desensitization and re-sensitization of the receptor are controlled via clathrin-mediated receptor internalization and recycling.1 This dynamin-dependent internalization can be triggered by antagonists or agonists of the receptor and exists to allow the recuperation of signaling competence.1 Long-term use of 5-HT2A antagonists has been shown to downregulate 5-HT2A expression1 and, while the mechanism of this "paradoxical regulation" is unknown, it is likely due to functional regulation.
https://www.reprocell.com/blog/biopta/5ht2a-serotonin-receptor#:~:text=5-HT2A receptor location,ligand binding experiments in rats.