Is he "microdosing" in an attempt to fix his anxiety, or going off on full-blown, eight-hour trips through the bendy world?
An acid trip is a mind-broadening experience, always supposing it's not a bad trip (which can be like the most horrendous waking nightmare ever). I actually think everyone should do it once, just to find out some of the incredible things your mind can do. Thing is, you'd need to be in the sort of safe, comfy environment conducive to an enjoyable experience, with people who know how to bring you around if you start going down a dark path. I only did it twice, in my adventurous youth, then stopped because I was getting 'trippy' afterwards. That went on for a few years.
There's no real evidence that "microdosing" does any good outside of a clinical setting, where it's used as an aid to psychotherapy. Some reports of reverb experiences like the ones I had.
It's not risk free by any means, especially with a user who already has some psychological fragility. Plus, it's illegal. In your situation, @Bohoboho, it's not very good that he's been doing this quite significant thing behind your back for so long. That's a good enough reason to end it. If you need a second reason, he clearly has some difficulty living in the everyday world and isn't likely to stop trying to escape from it.