Other Causes of Psychedelic Tolerance?

[Shampoo]

With a little research, either here or in a pharmacology book, one can easily find explanations for the neurochemical cause of the development of a 'tolerance' to psychedelics.

The repeated agonist binding of psychedelics to 5-HT receptors, particularly those of the 5-HT-2A, and 5-HT-2C results in the 'downregulation' of these receptors, which for all intents and purposes, can be imagined as the overstimulated receptors receding into the postsynaptic density/membrane so as to avoid more stimulation, becoming inaccessible to more incoming neurotransmitters or foreign chemicals (psychedelics).

However, there is a problem here. Repeated administration of psychedelics daily will result in a total tolerance by the fourth day, as has been shown in experimental settings (Nichols, 1997). Psychedelics which have been shown to do this include LSD, Psilocybin, Mescaline, and many of the RCs that are primarily 5-HT agonists (2C-xs, DOxs, substituted tryptamines..etc.). The contradiction lies primarily within Mescaline, which has been shown repeatedly to exhibit a tolerance very similar to other psychedelics, however, it has also been shown to not result in the downregulation of 5-HT receptors!

So, what other mechanisms underly psychedelic tolerance? Are there subjective factors involved in perspective shifting following an experience? Is there evidence of other neurochemical reactions that could cause tolerance, like phosphorylation of receptors?

Please discuss, I'll be here.