I think micro-dosing is generally seen as anything below a threshold dose (where you start to notice clear effects), but I’d probably include that level in my personal definition.
That level is obviously different for different people or at different times with different tolerances, so my answer to the poll was just a guess for myself right now.
Many drugs have effects that are noticeable long term or even soon after taking them without having a noticeable acute effect, but where you draw the line on the effects you’re getting or trying to achieve is not always clear.
For example, if you take an SSRI prescribed by a doctor and don’t notice anything after weeks, they may increase your dose until you report noticeable long term effects even if you don’t notice anything after taking them.
For some people those effects really make a difference, and for others it may not be worth taking them at all.
Once you pass a threshold dose of cannabis or psychedelics you’ll probably know quickly whether or not they’re having positive effects on you, but below that dose you may have to pay closer attention to what’s going on in your body and especially mind to know whether or not it is having an effect you still want.
If we extend the discussion to other non-psychoactive drugs (which you could include real micro doses of cannabis in), then you may never notice anything except in long term health effects, and I don’t think we have a lot of data to tell us what if anything we should expect to see from long term micro-dosing of cannabis.