Mushroom and LSD tolerance is not completely understood. It is; however, short-lasting. One can trip just as hard in three or four days as if they had never tripped before.
Psychological adjustments; however, are different. Eventually, if overdone, mushrooms will lose their magic. This is because the mind relishes novel experiences, when you take away the novelty of it, when you make it a way of life, that relish is lost. There is no quick-fix or supplement to save you from that.
5-htp, as the precursor to serotonin, would not have a great effect on your trip. The Psilocybin in the mushrooms is a serotonin agonist, which means it effects not the serotonin itself, but the receptor that takes that serotonin in. Its effects on MDMA are different BECAUSE MDMA actually causes the receptors to pump out serotonin, so more serotonin for them to pump means a harder roll.
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