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Cause, it would appear:

https://www.theguardian.com/society/2015/feb/16/skunk-cannabis-triples-risk-psychotic-episodes-study

And there is plenty more. And this discusses how important CBD is:

https://www.newscientist.com/article/dn26988-skunks-psychosis-link-is-only-half-the-cannabis-story/

I am not anti-drugs (especially not anti-cannabis) by any means, and I realise that a lot of smokers won't find it easy to accept. But the evidence is stacking up.

Do your own research, if you are really seeking a balanced view.