Because of my scepticism, I was alerted when I saw the BJPsych editorial on cannabis and psychosis, which began, “It is now incontrovertible that heavy use of cannabis increases the risk of psychosis”. As I said in a previous post, some “heavy users of cannabis may be rarely unintoxicated, leading to misdiagnosis of the induced psychotic-like experiences, which are usually transient in less heavy users”. But I ended that post with the conclusion: “The causal link between cannabis and psychosis has not been proven”.
The new editorial of course recognises that association does not mean cause. But it suggests that alternative explanations have been disproved. As I keep saying, the use of cannabis can cause emotional problems and people may use it to deal with their emotional problems. These problems may well be worse with skunk compared to hash (see Guardian article). Cannabis use is likely to be a proxy measure for poor premorbid adjustment associated with psychosis. I can't see that this most obvious explanation has been eliminated.