The effort is purely descriptive and does not seem to correlate the various effects with their cause (nothing wrong with that, still interesting).
This article provides a good overview of various theories:
https://www.quantamagazine.org/a-math-theory-for-why-people-...
Once a week for 10 years? Everyday for almost 2?
In their case they were taking lower doses than are traditionally associated with the one-off stories you hear about people traveling for ceremonies. There is also a tolerance build up that lessens the overt effects.
However, it still resulted in some major mental health issues over time. He was outwardly happy and cheerful, but the longer you talked to him the more you realized he had developed impossible ideas about reality, distorted (and easily debunked with photos and other records) memories of past events, and a lot of mystical ideas about the world.
He had mostly learned to hide them from people who weren’t in his group. When you got a couple of them ayahuasca people together and they started talking about mysticism, telepathy, and dismissing “western science” it started to reveal how far he was down the rabbit hole.
He has since gone MIA, though we get signs that he’s still alive and active from time to time via social media. The way it changed him was scary, though.