Most psychiatrists I talked rejected the notion that cannabis causes schizophrenia. They mostly claim genetic causes. My personal opinion from observing close people to me is that if you have predisposition, a psychoactive substance can be enough to nudge you over the edge into psychosis. It's a snowball effect. Of course, more likely is it would be something that raises your dopamine levels, like speed (amphetamine) or cocaine.
I’ve had the opposite experience but maybe it depends on the demographics of the patients that those psychiatrists see. As this peice points out, clinicians are increasingly likely to see the causal link even if researchers are having a hard time establishing that link.[0] I think a large part of that is due to measurement issues and methodological difficulties I alluded to. It took many years to establish the link between cigarettes and cancer. There are scientists who argue against global warming too. So much of science is driven by bias and group think and the pendulum has perhaps swung too far on cannabis. You might ask the psychiatrists you talk to what percentage of their patients with bipolar/schizophrenic type disorders are regular cannabis users.
