Mr 'Paul P' and the Truth

In a comment made today on the 'Cannabis and mental illness...' thread, Mr 'Paul P' wrote (amongst other things):

 

'The premise of Mr Hitchens' argument is that cannabis is all bad. A molecule of cannabis will lead to mental illness.'

 

I challenged him to justify this claim with referenced quotation. In a later posting, in which he is clearly aware of this challenge, he did not do so.

 

I now repeat the challenge. I require an answer.