Microdosing, or
micro-dosing, is a technique for studying the behaviour of drugs in humans through the administration of doses so low ("sub-therapeutic") they are unlikely to produce whole-body effects, but high enough to allow the cellular response to be studied.
As mentioned, this term is now used with magic mushrooms or psychedelics for one new vein of microdosing.
The real/original microdosing definition relates to a more formal aspect, "phase zero" on drug development--before clinical phase 1, to to predict whether a drug is viable for the next phase of testing. Human Microdosing aims to reduce the resources spent on non-viable drugs and the amount of testing done on animals. These amounts are typically 1/10 of the normal dose.
So the recent psychedelic explorations stole the term, which is fine by me as language is alive. They use small amounts for their experiments.
IMO, many on here do microdose---take small amounts (like 1/10 a normal dose) and they do not have whole body effects.
The dose is high enough to get cellular response yet not a whole-body effect.
I'm still calling it microdosing cannabis.
Just like a "dab" of Bryllcream will do ya' evolved into a current dab definition, microdosing is different in different contexts.
Another definition of it is:
Less commonly, the term "microdosing" is also used to refer to precise dispensing of small amounts of a drug substance. For example, a 0.012 g dose of cannabis???
If 1/10 of a dose of magic mushrooms is microdosing, so is a small dose of cannabis.
"Micro-dosing" = different definitions for different arenas, from formal new drug studies to recent psychedelic use to cannabis use.
It's the evolution of language, whether you like it or not.