i have little experience with stimulants, and have no formal knowledge of any of this stuff, so take what i say with a grain of salt, but i just learned on the other thread that psychedelia (at least in the classic, serotonergic psychedelics) comes from molecules differents from serotonin (in case, the psychedelic drug) binding to the 5HT2A receptor. serotonin binding to this receptor produces our normal, sober perception, and other shit binding there produces psychedelia.
but i think that higher than normal levels of serotonin wouldn't produce psychedelia (because you'd still have only serotonin binding to the receptors), more like serotonin syndrome. i believe a stimulant would have to bind to the serotonin receptors to produce psychedelia (such as MDA does i guess) not just raise serotonin concentrations.
from a more practical point of view, i never notice a hint of psychedelia with coke (though i'm not an experienced user). some people say they get mild psychedelia from MDMA but i believe that this could come from some affinity to 5HT2A, and not to its serotonin releasing properties.
i do hope someone with more knowledge on this subject comes by and says something though
The thing about the 5-HT
2A receptor that makes it interesting, and makes this subject more complex is the fact that it has multiple activation pathways. The reason why serotonin doesn't produce psychedelia even though it binds to 5-HT
2A is because it only activates the receptor in one of two possible ways. This is also why there are some other compounds that bind to 5-HT
2A and yet are devoid of psychedelic effects. It is possible for a compound to be an agonist at one pathway and an antagonist at the other. For example, before it was known that 5-HT
2A had multiple pathways, I believe 2C-B was found to be an antagonist at the 5-HT
2A receptor, and this was baffling, because it clearly produces effects consistent with classic (as in 5-HT
2A-agonistic) psychedelics. Later, the multiple pathways of the receptor were discovered, and it now seems that 2C-B is an antagonist at the pathway which is activated by serotonin, but an agonist at the pathway which is required for psychedelic effects. I'm not at home now, but if anyone wants a source for this I can post one a little later. Anyway, the point is, that it doesn't just take a compound that is not serotonin binding to 5-HT
2A to produce psychedelia, it also has to activate the correct pathway.
I hope this helps to answer your question regarding why serotonin doesn't produce psychedelia even though it binds to the correct targets.