Is Cannabis ‘driving us mad?’ Or is madness driving us to Cannabis?

Today’s article in the Spectator may have read very differently if the Author had heard the President’s Lecture at the Royal College of Psychiatrists (RCP)

On Wednesday, Professor David Nutt took on one of the greatest challenges in drug reform advocacy, explaining to a room full of psychiatrists that a regulated cannabis market would be better for society than the current black market. It’s a tough sell.

Psychiatrists are notoriously anti-cannabis legalisation, (although the RCP have announced they are reviewing that stance) and it’s not hard to see why: their patients are unwell and exhibit a higher rate of cannabis use than the general population. The stats on cannabis abuse vary widely, depending on factors such as the age or gender skew of the participants, but a meta-analysis of 28 papers showed 27% of  schizophrenia patients would suffer a cannabis-use disorder in their lifetime.

Confronted by such strong associations of cannabis use and mental health disorders,  it’s understandable why Mary Wakefield’s article today asks, is cannabis “driving us mad?” The answer is looking increasingly likely to be the opposite, madness is driving us to cannabis. Professor Nutt pointed out that over his lifetime the rates of cannabis use in the UK have grown massively. From 1969, when he was a student, there were half a million people in the UK who had used cannabis. Now that figure stands at ten million, a 20 fold increase in users which Nutt estimates “probably equates to a 100 fold increase in the amount used”. If cannabis use was causing schizophrenia and psychosis then we would expect the incidence rates to correlate with increasing use, ceteris paribus. However, research has shown that UK rates of schizophrenia and psychosis have flat-lined or even dropped in that period.

Wakefield acknowledges that many of these arguments could be dismissed as “correlations, not causes. But there’s nothing wrong with pointing out correlations — especially when the stakes are so high.” So let’s point out these correlations, and delve into the detail.


The landmark study linking cannabis use with schizophrenia is undoubtedly the 1969 Swedish conscript study which followed 45,000 young Swedes and measured their cannabis use and schizophrenia rates over 15 years. It did suggest that cannabis use could cause schizophrenia but at such a low rate that one would need to prevent 5,000 young men or 7,000 young women smoking cannabis in order to prevent one case, according to Professor Nutt. While the fact cannabis causes schizophrenia has taken such a hold in the public imagination, there hasn’t been room to contextualise the low probability.

A point that is rarely raised is explaining why so many schizophrenic patients use cannabis. According to Nutt there are three reasons: some are dependent, some are using it to overcome adverse effects of antipsychotics medicines and others are self medicating. It is this last point that is the most interesting. Professor Nutt said when asking patients why they use cannabis they report they can “think differently, instead of being locked in complete rumination about the voices or paranoia, even though that might get worse when they smoke cannabis, they can appreciate more of the world.” Patients finding relief in cannabis use may pave the way for better treatments. This aligns to the studies that have suggested CBD shows some potential as a cure for schizophrenic symptoms.

Wakefield also presents other arguments against cannabis, the murder rate in Washington has risen since legalisation: ‘in the US state of Washington, the first to legalise marijuana, the crimes of murder and aggravated assault have risen far faster than national averages’. Yes, there was a rise in murders which was described as not statistically significant by one report which also showed Oregon’s rate dropped after legalisation. Does legal cannabis cause murders in Washington and prevent them in Oregon? In this instance it’s easy to see how correlation falls short of cogence.


Twitter user @Wiki_Vic countered Wakefield’s correlations with some interesting counterpoints

Perhaps more convincing is Wakefield’s argument that “Researchers studied more than a thousand patients released from a psychiatric hospital and discovered that the ones who smoked dope were more than twice as likely to be violent. In a way it’s no surprise. Neuro-imaging shows clearly that chronic weed smokers wither their prefrontal cortex, the part of the brain that inhibits impulsive behaviour.” Here we have a correlation and a proposed mechanism of action. Let’s put aside the question of whether the violence was caused by cannabis or if violent personalities are more drawn to cannabis and look into the effects on the brain. It is true that heavy use of cannabis has been associated with a reduction in the size of the orbitofrontal cortex but at the same time there appears to be greater connectivity within it,  Nutt says this increased connectivity may be interpreted as having an effect on creativity and be the mechanism that allows patients to think differently. But even if cannabis does cause damage to the brain the best solution is still a regulated market because a regulated market can ensure the forms of cannabis available are the least harmful.

We have previously looked at how leaving cannabis in the black market creates a situation in which dealers are incentivised to smuggle more potent cannabis. This stronger cannabis is high in THC and low in CBD. Professor Nutt presented brain scans from a forthcoming paper [this article will be updated when it’s available] showing this high THC cannabis, “skunk has a profound effect to disrupt the network of brain functions especially the insula which is one of the most important emotional sensors in the brain.” Cannabis containing CBD did not cause this disruption. Banning cannabis due to its effects on the brain has paradoxically led to greater harm as the cannabis that is smuggled is stronger and not ameliorated by the presence of CBD.

One final point on drugs effects on the brain from the lecture is, “the reality is that the drug that really damage the brain is alcohol… alcohol is only drug we know categorically damages the brain. There is no question that alcohol damages the brain, there are serious doubts whether any other drug does… even strong high doses of crystal meth really damages the brain.” Advocating the continued criminalisation of cannabis without advocating the same for alcohol is logically inconsistent, and the futility of alcohol prohibition was well evidenced.


The current criminalisation of cannabis does not prevent its wide spread use as Wakefield laments, “the smell of London is now cannabis.” What she and other critics are failing to see is that the harms of cannabis are exacerbated by its criminalisation. Despite being illegal, cannabis is ubiquitous, the consequence of its illegality is it takes on a potentially more dangerous form. Regulation could compel cannabis to contain neuroprotective CBD elements as well as open the floodgates for research into medicinal effects (the current treatment makes it very difficult for researchers to handle the plant).

Fortunately it appears the RCP is opening up to this viewpoint, its the head of policy, registrar Dr Adrian James, told the Telegraph “As a forensic psychiatrist, the strongest argument is decriminalising behaviour that is widespread and avoiding people getting caught up in the criminal justice system and ending up on a conveyor belt.”  

Perhaps even more telling, Professor Nutt’s lecture on the Cannabis Revolution was supposed to be a debate, but they were unable to find an opponent.

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