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Brazilian Journal of Psychiatry

Print version ISSN 1516-4446On-line version ISSN 1809-452X

Braz. J. Psychiatry vol.41 no.6 São Paulo Nov./Dec. 2019  Epub Dec 09, 2019 


Can we brace for a Canadian-type cannabis storm?

1Departamento de Psiquiatria, Faculdade de Medicina, Universidade de São Paulo (USP), São Paulo, SP, Brazil

Fischer et al.1 have now translated the 2017 Lower-Risk Cannabis Use Guideline (LRCUG) to Brazilian Portuguese. The LRCUG includes “a set of 10 recommendations on how cannabis users may most effectively reduce the risks for associated health harms,” being aimed at those who are already using cannabis. I offer the following comments on the recommendations:

Recommendation 1 – No comment.

Recommendation 2 – “… most clearly that which begins before age 16 years… is associated with multiple subsequent adverse health and social effects…” – Cannabis interferes with the ‘pruning’ of synapses, myelination, and other milestones in the development and maturation of the nervous system since conception, and it does not stop at age 16. This recommendation could help prevention efforts by stating: “… initiation, if inevitable, should be delayed until full adulthood (age 22-25 years).”

Recommendation 3 – “… it is advisable to use cannabis containing high CBD:THC ratios” – High doses of CBD may lead to dissociative states.2 A safer recommendation might be: “Do not use cannabis. If you cannot abstain, avoid preparations rich in THC and low in CBD.”

Recommendation 4 – The authors consider the available evidence limited. Synthetic cannabinoids are full agonists of cannabinoid receptors, are more potent than THC, are clearly associated with psychotic states, and may be more neurotoxic than phyto-cannabinoids.3

Recommendation 5 – “it is… preferable to avoid routes of administration that involve smoking combusted cannabis material (e.g., by using vaporizers or edibles)” – Vaping is increasingly used in North America, including by minors, which involves the possibility of inhaling high THC concentrations from cannabis oil, wax, or liquid preparations.4

Recommendation 6 – “… avoid practices such as ‘deep inhalation’ breath-holding, or the Valsalva maneuver… as these practices disproportionately increase the intake of toxic material into the pulmonary system.” – This recommendation could mention the higher blood and brain levels of THC and other cannabinoid substances, with their own toxic effects from these maneuvers.

Recommendation 7 – “… keep cannabis use occasional (e.g., use only on 1 day/week, weekend use only, etc.) at most.” – In a cohort of 50,000 Swedish Army conscripts, it was found that using cannabis 50 times (e.g., once a week for one year) by the age of 18 (in 1969) resulted in a 3.7 higher risk of schizophrenia, a 2.2 higher risk of brief psychosis and a 2.0 higher risk of other non-affective psychoses. Contrary to what Fischer et al. claim,1 the risks of schizophrenia and depression are not the same, and schizophrenia carries a much worse prognosis. Other consequences from cannabis use include amotivational syndrome, impaired memory, schizotypal personality features, and subsyndromal psychotic symptoms.

Recommendation 8 – No comment.

Recommendation 9 – “There are some populations at probable higher risk for cannabis-related adverse effects who should refrain from using cannabis. These recommendations, in part, are based on precautionary principles.” – Experts used to dismiss the evidence that cannabis causes dependence. Telling dependent pregnant women to stop using cannabis is not enough. Young-Wolff et al.5 report the increased use in California from 2009 to 2018. As for cannabis and schizophrenia, the evidence that has accumulated since 1987 is overwhelming. A multisite investigation of patients admitted for their first episode of psychosis at 11 sites in 10 cities in England, Holland, France, Spain, Italy and Brazil6 found that daily cannabis use was associated with a 3.2 higher risk of psychosis. Daily use of high-potency cannabis (10% THC content, irrespective of CBD) raised this risk to 4.8 – assuming causality, the population attributable factor for cannabis indicates that 12.2% of first episodes of psychosis could be prevented by the eliminating daily use of high potency cannabis (the reduction for London and Amsterdam would be 30% and 50%, respectively, due to the higher THC content). Alcohol, tobacco, LSD, heroin, cocaine and crack are not associated with a higher risk of schizophrenia. Cannabis is not less harmful than alcohol or tobacco – they have different profiles of harm.

Recommendation 10 – “… it is likely that the combination of some of the risk behaviors listed above will magnify the risk of adverse outcomes from cannabis use… a focus for prevention. [Evidence Grade: Limited]” – This, too, is obvious, but as a focus for prevention it should not downplay the magnitude of the available evidence.

Medical ethics does not endorse social experiments merely for the sake of scientific knowledge or for less humanitarian objectives. Let us hope our nation will not be exposed to such a risky trial. If it is, perhaps we should brace for it.


1. Fischer B, Malta M, Messas G, Ribeiro M. Introducing the evidence-based population health tool of the Lower-Risk Cannabis Use Guidelines to Brazil. Braz J Psychiatry. 2019;41:550-5 [ Links ]

2. Hall W, Hoch E, Lorenzetti V. Cannabis use and mental health: risks and benefits. Eur Arch Psychiatry Clin Neurosci. 2019;269:1-3. [ Links ]

3. Waugh J, Najafi J, Hawkins L, Hill SL, Eddleston M, Vale JA, et al. Epidemiology and clinical features of toxicity following recreational use of synthetic cannabinoid receptor agonists: a report from the United Kingdom National Poisons Information Service. Clin Toxicol (Phila). 2016;54:512-8. [ Links ]

4. Borodovsky JT, Lee DC, Crosier BS, Gabrielli JL, Sargent JD, Budney AJ. U.S. cannabis legalization and use of vaping and edible products among youth. Drug Alcohol Depend. 2017;177:299-306. [ Links ]

5. Young-Wolff KC, Sarovar V, Tucker LY, Conway A, Alexeeff S, Weisner C, et al. Self-reported daily, weekly, and monthly cannabis use among women before and during pregnancy. JAMA Netw Open. 2019;2:e196471. [ Links ]

6. Di Forti M, Quattrone D, Freeman TP, Tripoli G, Gayer-Anderson C, Quigley H, et al. The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe (EU-GEI): a multicenter case-control study. Lancet Psychiatry. 2019;6:427-36. [ Links ]

Correspondence: Valentim GentilE-mail:

Disclosure The author reports no conflicts of interest.

How to cite this article: V Gentil. Can we brace for a Canadian-type cannabis storm? Braz J Psychiatry. 2019;41:471-472.

Creative Commons License This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.