frontline volume 2, issue 7 June 2008

Reefer madness?
cannabis and mental health

Andrew Gray is a psychologist and SSP activist in Glasgow. In this article he looks at the debate on cannabis from both a political and healthcare perspective.

Bureau Official: Here is an example: A fifteen-year-old lad apprehended in the act of staging a holdup - fifteen years old and a marijuana addict. Here is a most tragic case.
Dr. Carroll: Yes. I remember. Just a young boy... under the influence of drugs... who killed his entire family with an axe.
Reefer Madness (1936)

They are not hard to find. Every few days brings a fresh tale of feral youths meting out random acts of violence with unfathomable intensity. Apart from the shocking brutality, the speed with which a seemingly trivial argument or confrontation can assume murderous proportions, the stories have a common theme: the perpetrators of the violence, often in their very young teens, were high on 'skunk' at the time.

'Hippie dream, modern nightmare', The Observer (2008)

In May of 2008, Jacqui Smith the Home Secretary announced that cannabis was to be reclassified as a class B drug, reversing the 2004 decision of her predecessor David Blunkett to downgrade it to class C. This decision directly contradicted the advice of the governments own panel of experts, the Advisory Council on the Misuse of Drugs (ACMD), who, in a report commissioned by Smith herself, had concluded 'after a most careful scrutiny of the totality of the available evidence' that cannabis should remain a class C substance.

Smiths decision -taken with the full support of Gordon Brown -was predictably welcomed by the leader writers of the Daily Mail, who praised Browns 'moral courage' in overruling 'the so-called experts' and sending out 'a strong message that taking cannabis is harmful and wrong'.

Moral Panic

It would be easy to dismiss this story as just one more example of Brown pandering to the conservative press in a desperate attempt to reverse the seemingly inexorable decline in his governments popularity. Concern about the possible deleterious effects of cannabis on the physical, mental and moral health of the nations youth is not confined to right-wing tabloids however -the idea that the drug may not be as benign as its proponents have suggested has become an accepted part of the debate around the legal status of cannabis. An understanding of the current scientific evidence on the issue is vital for those campaigning for a more rational drugs policy.

Concern about the health risks posed by cannabis is not a modern phenomenon. In the 1920s the letters column of the British Medical Journal regularly featured accounts from doctors in the colonies of cases of hashish use causing insanity. Interest in the subject in the popular press was fuelled by concern that the practice was being brought to Britain by immigrants. The Daily Chronicle reported that there was 'a serious growth in the traffic of hashish, a deadly Eastern drug which induces madness in this country'. Overblown press coverage of this sort was at least partially responsible for an amendment to Dangerous Drugs Act in 1928, which made possession of cannabis an offence in Britain for the first time.

In the 1930s in the US the newspapers of tycoon William Randolph Hearst ran a hysterical campaign against marijuana, printing chilling warnings of the dangers of the killer weed:

'Marihuana is a short cut to the insane asylum. Smoke marihuana cigarettes for a month and what was once your brain will be nothing but a storehouse of horrid specters. Hasheesh makes a murderer who kills for the love of killing out of the mildest mannered man who ever laughed at the idea that any habit could ever get him....'

'Was it marijuana, the new Mexican drug, that nerved the murderous arm of Clara Phillips when she hammered out her victims life in Los Angeles?... THREE-FOURTHS OF THE CRIMES of violence in this country today are committed by DOPE SLAVES -- that is a matter of cold record.'


Hearst was not entirely motivated by concern for the well-being of the American populace. He had large investments in the timber industry, and was worried that the development of hemp paper would damage his interests. The DuPont corporation also lent support to the campaign, wary of the threat that hemp-derived plastics could pose to its petrochemical business.

Hearst was a strong supporter of the the Marijuana Tax Act of 1937, the first attempt by the US Federal Government to regulate cannabis, and the brainchild of Harry J. Anslinger, director of the newly-created Federal Bureau of Narcotics. Keen to expand the power of his department, Anslinger used overt racism to convince white America that marijuana posed a deadly threat:

'There are 100,000 total marijuana smokers in the US, and most are Negroes, Hispanics, Filipinos, and entertainers. Their Satanic music, jazz, and swing, result from marijuana use. This marijuana causes white women to seek sexual relations with Negroes, entertainers, and any others ... Reefer makes darkies think theyre as good as white men.'

The American Medical Association opposed Anslingers legislation, and sent Dr William C Woodward to testify before the Senate:

'The Division of Mental Hygiene [of the US Public Health service] ... have had no record of any marihuana or cannabis addicts who have ever been committed to [federal treatment facilities]'

Anslinger has his own expert however, one Dr James C Munch:

Dr. Munch: The reason we use dogs is because the reaction of the dogs to this drug closely resembles the reaction of human beings.

Mr. McCormack: And the continued use of it, as you have observed the reaction on dogs, has resulted in the disintegration of the personality?

Dr. Munch: Yes. So far as I can tell, not being a dog psychologist...

Munch later published a book in which he recounted his own experience of taking cannabis, which, he claimed, had caused him to grow fangs and turn into a bat. Despite this his evidence was preferred to the testimony of the AMA, and the Marijuana Tax Act became law.

Seventy years later the debate has seemingly taken on a more rational tone. While the popular press is still happy to frighten readers with lurid tales of weed-fuelled violence and depravity, government figures insist that their drugs policy is based on scientific evidence. In particular they point to the new studies that link cannabis use with the development of psychotic illnesses like schizophrenia, and the availability of more powerful strains of herbal cannabis, so-called super-skunk. These developments, they argue, call for a reversal of the limited relaxation of cannabis prohibition that has been in place since 2004. As the Guardian reported in May 2008:

'Smith is expected to justify her decision [to reclassify cannabis] by highlighting the strength of 'skunk' strains of herbal cannabis now widely available. Gordon Brown last week warned of the 'more lethal quality' of much of the cannabis now available, described it as a gateway drug, and said that reclassification was needed to 'send a message to young people that it was unacceptable'.

So is there really any evidence to suggest that Britain is facing an epidemic of skunk-induced schizophrenia? Are more people using cannabis? Is it stronger than it used to be? What does it do to the brain?

Cannabis Use Declines

Figures from the British Crime Survey indicate that cannabis use has gone down rather than up since 2004. The percentage of 16-24 year-olds using it has fallen from 25.3% in 2003-4 to 20.9% now, and among those aged between 16 and 59 the proportion has gone from 10.8% to 8.2%.

Data in the ACMD report, based on reports of drugs seized by the police, suggests that most of the cannabis consumed in Britain is now produced on these shores, rather than being imported from traditional sources like Morocco or the Middle East. Suburban cannabis farms are springing up everywhere -more than 70 were discovered in Scotland alone in 2006/07. The crop that is produced is almost exclusively sinsemilla, which now accounts for an estimated 80% of the marijuana market in the UK.

Sinsemilla (a Spanish term that translates as 'without seeds'), refers to the practice of growing only unpollinated female plants, which typically contain more THC, the main psychoactive constituent of cannabis. Levels can vary widely, but sinsemilla on average contains about 14% THC, compared with about 4% in cannabis resin. Potency has been further increased by selective breeding to produce strains referred to as skunk, which can contain up to 20% THC.

Modern weed may be stronger than it used to be, but that does not mean that individual cannabis users are necessarily receiving higher doses of THC. People are able to modify their intake to achieve a required level of intoxication, in much the same way that most drinkers consume smaller volumes of spirits than they do of beer. The availability of more powerful forms of cannabis does mean it is now possible to 'binge smoke', but there is no evidence that this is widespread in the UK - hospital records show no increase in cases of acute cannabis intoxication over the last few years.

So it seems that there has been no increase in the number of people using cannabis, and most of those who do dont seem to be getting any more stoned. Unfortunately it is harder to be relaxed about the third danger cited by proponents of cannabis prohibition, the possibility that use of the drug may cause long-term mental health problems.

Mental Health

'Cannabis use and risk of psychotic or affective mental health outcomes', a paper published in medical journal The Lancet in July 2007, reviewed evidence from large studies into the link between cannabis and mental illness carried out in the US, Germany, Holland, Sweden and New Zealand. The authors conclude that cannabis use increases the risk of persistent psychosis (i.e. symptoms not attributable to transient intoxication) by about 40%, rising to 200%, or a trebling of risk, among frequent users.The paper is a high-quality piece of research, which as far as possible allows for the effect of confounding factors, and there seems little reason to doubt that these figures are accurate.

A 40% increase in risk is not as alarming as it sounds, since the baseline risk for psychosis is low. For schizophrenia, using cannabis will raise the risk from 1% to 1.4%. Still, when applied across the whole population, even a small increase can produce a significant public health problem. If this research is correct, about 800 cases of schizophrenia could be prevented each year in the UK if the consumption of cannabis ceased. However there is no evidence there has been any recent rise in the incidence of psychotic illness. Data gathered for the ACMD show that the annual number of new cases of schizophrenia has actually fallen in the period 1996 -2005.

It is clear from clinical experience that the risk of psychosis associated with cannabis use is not evenly distributed across the population. Some people can smoke heavily for years without any ill-effect, while others become unwell after relatively modest exposure. The most reliable predictor of sensitivity to the harmful consequences of cannabis use in a given individual is a past history of mental health problems. Certainly anyone who has personal experience of psychosis would be well-advised to avoid using cannabis. In people without any previous problems it is difficult to forecast who might be most at risk. Age, genetics, and environmental factors are all important, but research in this area is far from conclusive.

Some studies have shown that the effect of cannabis on psychosis risk is more marked when it is first used before, as opposed to after, the age of 16. This seems logical, since the brain of an adolescent is still developing, and is presumably more vulnerable to whatever effect cannabis may have. Other research has failed to replicate this though.

The genetic picture is extremely complicated, due to the huge number of genes that are involved in the regulation of brain function, and the still very limited body of knowledge on how they interact with each other, and with the environment. In general terms, anyone who has a family history of psychotic illness will be at higher risk of having problems with cannabis than a member of the general population.

As yet no particular genes have been definitely identified as being responsible for increased susceptibility, though there are some promising areas of research. One involves catechol-O-methyl transferase (COMT), an enzyme associated with the regulation of neurotransmitters, chemicals which carry messages between brain cells. COMT is connected with the function of the neurotransmitter dopamine, over-activity of which is strongly linked to psychosis, so it is plausible that the effect cannabis has on the development of psychotic illness is due to some interaction with COMT.

There are two different forms of the gene that codes for COMT, known as Val and Met (depending on which amino acid, valine or methionine, is at codon 158 of the gene), which produce COMT with higher and lower activity respectively. Since everyone has two copies of each gene, people can Met-Met (25% of the caucasian population), Met-Val (50%) or Val-Val (25%). Cannabis-associated risk seems to be strongest for Val-Val, intermediate for Met-Val and absent for Met-Met, though this only holds true for adolescent exposure. The exact mechanism of this is still unclear.

The COMT research, and work on several other genes that may be implicated in the development of psychosis, is likely to shed some light on why some people are more sensitive to the effects of cannabis than others, but prediction of an individuals personal risk based on their genetic make-up will not be possible in the foreseeable future.

There are many other environmental factors associated with the development of psychosis, including family relationships, adverse life events, socio-economic status, and other substance use. Unfortunately there is practically no reliable research into how these interact with cannabis use to modify the overall risk.


It does seem clear then, that while tales of dope-crazed youth running amok are as fantastical today as they were 70 years ago, cannabis consumption is not without its hazards. Does this information adversely affect the case for legalisation? Or does an appreciation of the risks associated with cannabis actually strengthen the argument against prohibition?

The more that is discovered about the possible harmful effects of cannabis, the more obvious it is that use of the drug should be treated as an issue of public health, rather than criminal justice. The current system of legal proscription has produced a situation where cannabis availability is essentially unregulated, and where it is difficult to transmit information on the potential dangers of cannabis use to those most in need of it.

An alternative policy would be to bring cannabis into the category of legally-available drugs, alongside alcohol and tobacco. This would not be a panacea, but would at least provide a framework within which efforts could be made to monitor and regulate use of the drug in populations most at risk of adverse consequences, as well providing a point of contact for disseminating public health messages. Other benefits would include the facilitation of further research, the provision of taxation revenue to fund treatment programmes for problem users, and a reduction in illegal cannabis production and associated criminality.

Sadly, it is unlikely that such a course of action will be followed by any level of government in the near future. When the Scotlands Futures Forum, Holyroods own think-tank, produced a report earlier this year proposing, among other measures to reduce the impact of drugs and alcohol on Scottish society, the legalisation of cannabis, it met with a cool response from the Scottish Government, and outright hostility in the press. Perhaps the debate around cannabis use hasn't moved on very far since the 1930s after all. We shall leave the last words to an expert:

Dr. Carroll: ...The next tragedy may be that of your daughters... or your sons... or yours... or yours... (pointing directly at the camera) ...Or yours!

Further reading:

Cannabis: Classification and Public Health - Advisory Council on the Misuse of Drugs

The Scotlands Futures Forum report into drug and alcohol addiction (PDF)

Poisons, the police and the Pharmaceutical Society: cannabis and the
law in the 1920s

Why is Marijuana Illegal? A brief history of the criminalization of cannabis