The recent wave of legalisation of marijuana for recreational use across the USA and Canada has increased the public’s perception that it is a relatively harmless drug. Unfortunately, as former New York Times journalist Alex Berenson explores in his new book, this could not be further from the truth.

The title ‘Tell Your Children’ suggests that the book will be a cautionary tale and in this regard it does not disappoint. It starts out with a grisly case of a paranoid mother murdering her children, with all the psychiatrists and judge in the case agreeing that her cannabis use had played a significant role in her developing schizophrenia and the violence that followed. The mix of often shocking anecdotal evidence/cases with cold clinical evidence is a recurring theme throughout the book and is used to good effect. Berenson makes no apology for the fact that he is specifically looking at the link between marijuana use, mental illness and violence and not at any supposed beneficial effects of the its legalisation for the economy or otherwise. Such is the well-researched nature of the book and the veritable mountain of evidence he finds by the end of the book, it would be very hard to argue with its key message.

The first part of the book takes us on a brief history of marijuana use and its association with psychosis, from the colonial Indian government’s realisation that ‘habitual use does tend to produce insanity’ to infamous US politician Harry J. Anslinger declaring it ‘a shortcut to the insane asylum’. Such proclamations were subsequently derided as government propaganda when widespread use of the drug began again as part of the 1960s counterculture, not helped by the fact that Anslinger was subsequently found to be racist and by the production of widely ridiculed government films such as ‘Reefer Madness’. Marijuana became associated with artists, free thinkers and musicians, and its continued illegal status was viewed as a means of social control by the government.

The AIDS epidemic of California in the 1990s led to a movement to legalise ‘medicinal marijuana’ for those with terminal illnesses. This was despite little if any evidence of any beneficial effects for the drug, and the fact that it was never approved by the Federal Drug Administration (FDA). California law is unique in that it allows a citizen to put forward a proposition that will become law if voted through by the public. Posters depicting dying patients asking for their medicine and the funding of wealthy backers led to the proposition passing comfortably. The author points to this as a key turning point in the public perception of marijuana, now as a medicine rather than a drug, and the sowing of seeds which led to eventual legalisation for recreational use in many US states and Canada.

The idea of marijuana as a medicine is somewhat ironic in the context of this book, given the large amount of evidence the author presents as to its detrimental effects on both the mental and physical well-being of the individual. While the link between marijuana use and psychosis had always been suspected, it was a large-scale study of Swedish army conscripts that provided the first solid evidence to support this claim. Swedish researcher Sven Andreasson realised that Swedish conscripts had to answer a questionnaire regarding past drug use when joining the army. He cross-referenced this historical data with those who went on to develop psychosis and found a clear association between cannabis use and psychosis. His subsequent paper published in the Lancet spurred a new wave of research into the topic and brought it back to public awareness.

Confessing that he is neither a clinician nor a scientist, the author does an excellent job of compiling evidence for an association between cannabis and psychosis, and he interviews several of the leading experts in the area, including Sven Andreasson, Robin Murray and Mary Cannon. The second part of the book is entitled ‘Proof’ with a chapter ‘Study After Study After Study’. By the end of this section, even the most sceptical reader would have a hard time arguing against the evidence.

The book also presents the human stories behind the numbers, with anecdotal cases of lives ruined and families torn apart serving as a reminder of what this drug can do. In a chapter entitled ‘An epidemic arrives’, Berenson finishes part three of the book with reports from those working on the ground with large-scale data. Evidence is discussed that the numbers presenting with psychosis are increasing with the increasing availability and strength of Marijuana. This evidence has largely been ignored by society and is a real concern for health services and public health into the future.

In the final part of the book, ominously titled ‘The Red Tide’, Berenson finishes the book with a mix of research and unfortunate case studies relating to cannabis-induced violence. Some of these stories are truly frightening and horrific, from parents killing their children to individuals brutally murdering complete strangers. Berenson reminds us that, contrary to the common perception of the docile stoner, in some individuals, cannabis has the paradoxical effect of causing aggression and violence, and he points to mounting evidence to back up his claims.

Overall, this well-researched, gripping and at times shocking book serves as a timely reminder of the dangers of cannabis that should not be ignored. The wave of positivity surrounding cannabis legalisation across many states should come with a warning: cannabis is not a medicine, and its use can have severe and life changing consequences. Tell your children.