It has been my experience that meditation has increased my sensitivity to psilocybin.
Fairly early on (pre stream entry and pre jhanas in meditation terms) I experimented with around 2 grams of mushrooms, eventually working up to a peak of around 6 grams. But at some point (after stream entry) I slowly began to notice that higher doses seemed to be a bit too much, that there was a certain load of tension from the drug that I found unpleasant, and I've been decreasing the doses of my "experiments" ever since.
Even last summer I was tolerating doses of 1 or 2 grams, but that seems a bit much now. I've experimented with low doses before, but now I'm getting into a range that some might legitimately consider a microdose. Lately (post 2nd path) .06 - .08 grams seems to be plenty, and I've alternated with doses of around .15 - .17 grams which now seem slightly high. My guess would be that .06 - .08 grams might barely get the average person to the equivalent of a mild cannabis high.
The early FMRI research showing similarities between the effects of psilocybin and meditation might explain this. Or, I could be an anomaly.
At these lower doses I don't get nearly so much in terms of visuals, but the "mind-freeing" aspect seems to work just fine, which is mainly what I'm looking for. Higher doses seem to cause this tension that I referred to, kind of playing off the stimulant effects of the drug, and seem to emphasize the more unpleasant aspects (dukkha).
I would also mention that I haven't noticed this kind of "reverse tolerance" in other recreational substances that I use, i.e. cannabis, alcohol, and nitrous oxide. Just psilocybin.