"I have no doubt that breathwork can make altered states, but I very highly doubt it is comparable to drugs."I was super skeptical myself.. so much so that even though I'd heard of holotropic breathwork at least a couple of decades ago I didn't bother to try it because it just sounded like complete bullshit.
But I did eventually try it, about a year ago, and I was amazed that it did in fact induce a state that was comparable to at least a low dose of psychedelics. Some people have reported even more powerful effects.
I aborted my self-experimentation out of concern that it might cause long-term health effects (as, paradoxically, hyperventilation -- which is what holotorpic breathwork mostly consists of -- can cause oxygen deprivation to the brain) but at least now, one year later, I haven't experienced any adverse health effects that I can detect, so might give it another try.
The really long-term effects (like 10 or 20 years later) are still unknown, though, as there just haven't been any serious long-term studies of it.
Another interesting possibility (which is again, mostly unstudied by science yet) is combining breathwork with other means of inducing altered states of consciousness.