Re: Drug Abuse: Is Marijuana Harmful; Right Of Reply By Dr Femi Adebajo


I have just seen this very disturbing article: Drug Abuse: Is Marijuana Harmful published on August 24th, 2013 on this news portal and would like to offer a response, to correct the errors in the article and set the record straight. I have been a medical practitioner for over 20 years and practised and taught postgraduate psychiatry for over 15 years, so I have a professional interest in the subject, apart from a broader interest as a citizen. 

The link between marijuana and mental illness is not merely an ‘attribution’ but a scientific fact backed by the most robust level of evidence, appraised by trained professionals through rigorous peer-review processes. Ideally, to test the hypothesis that cannabis (marijuana) causes mental illness, one would formulate a null hypothesis (e.g. ‘marijuana does not cause mental illness’) and then experiment on a large-enough group of human subjects, matched with similar human controls. One would then be able to conclude that any observed differences in outcome are due to the intervention of interest (cannabis exposure) rather than any confounding variables and observational biases. That is the essence of the scientific method and avoids the vagaries of whimsical personal observations and anecdotal evidence- everyone knows one Uncle Brian or Auntie Elsie who has smoked cannabis for 150 years and is still going strong at the age of 190 years! 

Of course we cannot experiment on human beings so we must rely on the next level of the hierarchy of evidence- large-scale cohort studies, either prospective or retrospective. You take a large group of humans and look backwards (or forwards) at their exposure to cannabis and measure the outcome of interest (say mental illness). This process is helped by the good practice, in some countries, of keeping detailed health records on citizens throughout life. The Danish Cohort study is based on such a template and, along with similar studies, conclusively proves that cannabis causes mental illness in some individuals. To paraphrase, one might suggest that cannabis causes mental illness in some people but we can only guess at who those individuals might be. Therefore, those who use cannabis are unwitting (or maybe not!) participants in an experiment to test their vulnerability. 

It is also false to state that ‘marijuana has been found not to be harmful nor addictive and people need not be afraid of its usage’. Apart from the well documented effects on mental health, it is often missed that marijuana smoking is a leading cause of throat cancer, perhaps related to the lower combustibility of the resin (compared to tobacco) and hence the higher temperatures delivered to the upper respiratory passages. And you can add to this the effect on the germinal epithelium in the testicles leading to sub-fertility and infertility. On general terms, it requires no great speculative ability to imagine the potential harm from a cocktail of dozens of chemicals contained in the mixture known as marijuana- tetrahydrocannabinol (THC) is not the only active ingredient!

There are no credible ‘research studies indicating the medicinal, herbal, healing and curative qualities of marijuana’ although I would be glad to be advised if anyone knows of some. The objective appraisal of clinical research evidence is a technical skill that integrates quantitative (econometric) and qualitative approaches and we should be wary of making pronouncements about ‘research evidence’ if we do not have those skills. It goes way beyond a cursory reading of the first page of an internet google search or a happy-clappy circulation of mutually-reinforcing memes of misinformation and self-serving shibboleths. 

Having said all that, I am a social liberal and believe in the right of mature adults to make their own choices about all aspects of their own lives, including health and lifestyle, provided the rights of others, and society as an organic whole, is accommodated. Those who wish to smoke/eat/drink cannabis will find no medical alibi to back their personal choices in this regard.

Dr Femi Adebajo is a medical practitioner of over 20 years and practised and taught postgraduate psychiatry for over 15 years. He writes in from the United Kingdom.

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