Why have rates of schizophrenia stayed flat while cannabis use has increased, if cannabis is causal in schizophrenia?

Interestingly, this appears to be partly the result of having bred cannabis to have a very high THC content, while CBD shows some anti-psychotic effect[1]

1: https://www.theguardian.com/society/2014/nov/16/new-strain-c...

If you actually read the science around this, it's been shown that cannabis use clearly does not increase the overall incidence of schizophrenia in a population. It can be a trigger for those already susceptible to developing it, but so can any other sufficiently stressful life experience. This is just another anti-drug myth.

There was a large scale, long duration study which followed thousands of participants and found that the incidence of mental illness, including schizophrenia, in marijuana users was not higher than that in non-user populations. I'll see if I can dig up the study.