You can definitely overdo psychedelics and fuck up your mind if you are careless with them. Maybe read up a bit on erowid, dmtnexus, shroomery, plenty of warnings from people who went to deep. Don't be stupid and naive.
Microdosing may seem harmless, but it also means taking psychedelics every day for long periods. I wouldn't do more than 2 weeks, you gotta have to function without the drug at some point, can't imagine dosing LSD for a year and then stopping will be pleasant. But your mileage might vary... I just have way to much respect for psychedelics to take them every day.
He's asked for evidence and you've responded with a claim. Do you have any evidence to back this claim up?
>I've seen a friend of mine going deeper and deeper into that hole.
This is an anecdote. It does not constitute scientific evidence.