In 2004 the UK government stepped up it’s classification of the cannabis plant in part due to the tenuous links between cannabis and schizophrenia. It was claimed the use of high THC ‘skunk’ was increasing the threat of psychosis of the youth.
A curious thing happened. The hospital admission figures for cannabis incidents dropped. Strange but true.

Download and read this 2013  study on the subject:

Effect of reclassification of cannabis on UK hospital admissions 2013