June 2, 2014

Dear Sir,

The medical points regarding marijuana/cannabis use that need to be stressed are that the teenage brain is very different from an adult brain and suffers permanent damage from regular cannabis use.

This damage results in a lifelong loss of about eight points of IQ, doubles the risk of developing psychotic disorders such as schizophrenia, and alters human brain structures. See the discussion below for further details of the scientific studies related to these comments.

Legalising cannabis will automatically make it “more acceptable” and more readily available for teenage consumption. Any legalisation should be accompanied by taxation and those proceeds used to fund aggressive programs aimed, in all possible ways, at stopping cannabis use by teenagers and young adults up to the age of 21 years.

Significant criminal penalties should continue to be assessed for those who supply to teenagers and deal in designated school zones. Any less and we are accomplices in dimming our teenagers’ horizons.

There is no reasonable medical/scientific evidence supporting cannabis efficacy in cancer treatments or in neurological diseases such as multiple sclerosis, although there can be some symptom relief (nausea, pain, spasms, stiffness, etc).

Anecdotal comments from individual experiences regarding the use of a substance in medical treatments are generally met with a yawn in the field of medicine, if not disdain.

The foundation of medical science is controlled clinical trials where (usually) two large groups of patients are studied, one group who take the proposed treatment and the other who take a similar appearing or feeling treatment which is a placebo, and the outcomes are compared by researchers blinded to the treatments.

Developmental neuropathological studies show that the human brain matures until the early 20s and this coincides well with the facts presented below.

Researchers in New Zealand (Meier et al published in the Proceedings of the National Academy of Sciences in 2012) administered IQ tests to over 1,000 13-year olds before any cannabis use, then assessed their cannabis use intermittently over the next 20 years, retested their IQ at age 38 years, and finally compared the scores relative to the amount of their cannabis use.

Those who used cannabis most heavily in their teens and thereafter showed an average drop in IQ of eight points, enough to drop someone of average intelligence into the lowest third of the intelligence range. The participants who never used cannabis or started after age 18 showed no or minor declines.

Providing an anatomic basis for this is another recent study (Gilman and colleagues in The Journal of Neuroscience, 2014) who used advanced MRI imaging techniques to show that cannabis use started in the teenage or young adult years impairs the formation of brain connections and structures integral to intelligence and reward circuitry.

These provide further confirmation of a study reported in the British Medical Journal in which researchers followed 1,923 adolescents and young adults aged 14 to 24 for ten years and were able to prove that cannabis use was linked to the development of psychotic disorders, hallucinations and delusions, and was thus considered to be a contributory cause of schizophrenia, essentially doubling the risk.

Another study from Harvard Medical School evaluated 35 chronic marijuana smokers and compared them to 29 healthy people. Twenty of the smokers started before age 16, a further 15 started after age 16, and the average age at the time of evaluation was 22.

The subjects were given a standard test of brain executive function. The non-smokers performed better than the smokers, and the early-onset smokers did worse than the late-onset smokers, in some areas making twice as many errors.

These executive functions are performed in the last area of the brain to develop in adolescents, the prefrontal cortex, and the marijuana-induced damage appears to be irreversible.

I have reviewed some 40 plus scientific studies which have appeared in the medical literature over the last three years which generally support the above findings, without contradictions.

Other studies have shown that there are also deleterious effects of cannabis smoking on lung functions similar in many ways to those of cigarette smoke.

Of course, these brain and lung effects presumably then have many and widespread additional ramifications for society, leading to increased rates of mental health and lung diseases, hospitalisation and incarcerations.

Anyone who sees him or herself somewhere in these study groups should not try to bury these facts to the detriment of our upcoming youth.

Regarding any comparison with alcohol, this chemical has equally bad individual health implications and societal ramifications, but that genie is already out of the bottle. We should not repeat this mistake. The use of cannabis for legitimate medical reasons by prescription as a controlled drug remains reasonable.

KEITH H CHIAPPA, MD

Neurologist, Chief of Medicine, King Edward VII Memorial Hospital

Associate Professor of Neurology, Harvard Medical School (1986-2010)