> Even amongst mushrooms from the same rice cake, the dosage wildly varies
This is the main reason with psychoactive mushrooms overall. You can't dose exact via bio material so overdosing happens regular and could be actually harmful.
Would you mind citing a case of harm caused by pharmacological effects of mushroom overdose? My own online research since your post found no such recorded instances, but perhaps we're using different terminology.
Its hard to find serious papers about it because most of the time its due to "abuse" of drugs and (!) mixed consums.
Anyways, I had a friend who was really into mushrooms overall (not only psychoactive ones) and while he was pretty open to drug using he stated multiple times that overdosing can lead to bad trips and so called "hängenbleiben" (I dont now the english term, it means the trip never really stops).
Extracting from shrooms with ethanol is quite consistent, the psilocybin isn't very soluble so after a few days soaking you can be pretty confident that the ethanol has taken up all it can. for microdosing the ethanol probably isn't enough to worry about trying to take it back out of solution, drink .25 oz or so.
This is the main reason with psychoactive mushrooms overall. You can't dose exact via bio material so overdosing happens regular and could be actually harmful.