HONESTY NEEDED IN CANNABIS DEBATE

Every weekend Ben Goldacre ridicules "studies" that have no
double-blind, placebo-controlled data. But now you report as fact the
claim that cannabis causes schizophrenia (Cannabis use linked to 40%
rise in risk of schizophrenia, July 27), which is simply based on the
observation that some people with the disease have used the drug. To
my knowledge, the data would just as well support the alternative
explanation that people with a disposition for schizophrenia are more
likely to try and enjoy drugs even before their illness becomes
apparent. Or can you show me a systematic study where healthy
volunteers were given cannabis while others smoked a placebo?

Dr Michael Gross Oxford