That's exactly why I'm fascinated. I started inconsistently with 100mg of dry material, eventually moving toward a consistent schedule as the cognitive benefits became apparent. This is where the random headaches started. Then they gradually diminished over the course of a month and stopped completely before titrating to 200mg.Having now read the paper, it appears tha headache occurred at least sometimes even at the lowest dose in the study (5mg, standardised for bodyweight), and there appeared to be a correlation between dose size and both frequency and duration of headaches.
How does this measure up in comparison to your microdose?
Unfortunate, but also perhaps understandable, that there was no mention of controlling for coffee/caffeine intake in the study, although I've only skimmed the article so far and certainly haven't read the fine print!
I haven't noticed any side effects since. Just some minor oddness when I first began integrating Hericium erinaceus extract into my daily routine.