I've experimented with holotropic breathwork, and was quite amazed at the experience. Unfortunately, as much as I've tried to re-create the experience while not lead, I find my mind just doesn't want to go beyond about 5-10 minutes of breathing, vs the 30 minutes I did in breathwork sessions.

Having said that, I think the design of this study could be much improved. It shouldn't be too difficult to create a double blind group environment using headphones (think like a silent disco) where both participants and researchers don't know who is listening to guided or not.

I'm also not sure if the biomarkers are the best. DMT can apparently be detected in saliva, and I believe the theory is that during holotropic breathwork, the pineal gland releases more DMT than normal.