Marijuana: What science has to say

It's a drug that divides people: some see it as unfairly demonised, others as a medical catastrophe in the making. But what does the science say? Elizabeth Finkel investigates.

A cannabis plant grows in the Amsterdam Cannabis College in the Netherlands. – Christopher Furlong/Getty Images

It's a surprise to find a poster of brightly coloured marijuana leaves adorning the office of Melbourne psychiatrist David Castle. After all, Castle – a professor at St Vincent’s Hospital – is, with colleague Robyn Murray of London’s Institute of Psychiatry, the author of the prize-winning tome, Marijuana and Madness, a collection of scientific essays on the link between marijuana and schizophrenia. As we sit in his bright, roomy office, the youthful, denim-clad psychiatrist talks in his clipped South African accent, effusing sympathy for the plant that causes so much heartache to parents and endless social debate.

The sympathy is inherited, it seems. His mother, a renowned Cape Town doctor who was noted for her “interest in things slightly off the edge”, explored the medicinal uses of the narcotic weed during the 1950s. Castle has continued the family tradition.

As our discussion weaves through the data, I struggle at first to divine Castle’s message. Finally, it dawns on me. The psychiatrist is … I think … exasperated. “When it comes to the marijuana debate, science and rationality have very little to do with it: the truth about marijuana has been lost in the smoke of political rhetoric,” Castle tells me.

He is not alone. The ‘Marijuana Wars’ have waged for decades and there are numerous veterans who also have that exasperated sound.

Wayne Hall is former director of Australia’s National Drug and Alcohol Research Centre (NDARC), and now a professor at the school of population health at the University of Queensland. Australia has probably done more research on marijuana than anywhere else: a result of its high rate of use and ample research funding, Hall tells me. He has pondered the harms of marijuana for the last 13 years and his commentaries appear in prestigious journals, including a recent one on cannabis and schizophrenia in the January 2006 issue of The Lancet.

“It’s hard to get the real message out because the debate is so polarised. If it is perceived to be harmful, people want to go to war and lock up every user; if it is perceived to be harmless, they want to legalise it completely. The truth is that cannabis is a drug like any other – some people will experience difficulty,” says Hall.

On the scale of harmful substances, marijuana ranks fairly low.
Tobacco and alcohol exact a far greater toll.

It seems that after all the textbooks, the scientific papers, and the front-page headlines, it’s still the same old story: marijuana used in moderation is a relatively harmless drug. Pharmacologist Les Iversen, now a visiting Oxford scholar, tells me, “Marijuana is somewhat more harmful than aspirin”. Iversen should know; he spent 10 years assessing the risks of drugs for pharmaceutical giant Merck & Company, and recently served on Britain’s Advisory Council on the Misuse of Drugs.

On the scale of harmful substances, marijuana ranks fairly low. Tobacco and alcohol exact a far greater toll, between them accounting for some 12% of global deaths. Even aspirin is credited with causing in the vicinity of 50 deaths a year in Australia alone. No deaths are attributable to marijuana.

Yet in the war on drugs, marijuana continues to be singled out as the principal scapegoat. In 2005, some three quarters of a million people in the US alone were arrested on marijuana-related charges, about 89% of these just for possession. Even cancer patients who were using marijuana to ease their symptoms were among those arrested.

In Australia, the state of New South Wales recently toughened its laws, and Prime Minister John Howard has called for more to follow: “I will ask [the state premiers] to agree with me that part of the solution to the mental health problem is a tougher line on marijuana, and I imagine they will agree with me,” he said, ahead of a forthcoming summit with the states.

Marijuana has been demonised, says Castle, to the point that even its considerable medicinal and agricultural uses have been disavowed. The plant is extremely hardy, and has as much to offer the environmentally challenged world today as it did in times of old, when ‘Indian hemp’ provided the mainstay for ship sails and rope.

Some put the scapegoating of marijuana down to the conservative political tide sweeping Western democracies. Until 2004, Peter Cohen was the director of the Centre for Drug Research at the University of Amsterdam. The Netherlands, as any backpacker will tell you, is one of the few places in the world where you can legally buy cannabis. But marijuana use is still technically illegal: individuals can only buy up to 5 grams, and advertising its sale is not permitted.

A coffee shop in Amsterdam where laws have traditionally been liberal on marijuana usage. – Yadid Levy/Getty Images

For 20 years, Cohen’s centre documented the country’s experiment of decriminalising cannabis, allowing small quantities to be sold from the coffee shops that now outnumber butcher shops in parts of Amsterdam. His studies show drug laws have very little impact on the rate of cannabis use anywhere in the world. “There are enormous differences in the rates of drug use between countries,” he says. “We don’t really know why. For instance in the Netherlands, 17% of people have tried it; the UK rate is twice as high. We don’t think drug policy has anything to do with it.”

In his view, the direction of marijuana research is at the whim of the political climate. “There’s a fashion now to determine the cause of mental health problems; they want research that shows the harms of marijuana. But people’s lives don’t fall apart because of marijuana. I call it Soviet science – science geared to produce a political point.”

Alex Wodak is director of the Alcohol and Drug Service at St. Vincent’s Hospital in Sydney and Australia’s most colourful drug-war resistance hero. He agrees politics is a big driver in the marijuana wars. “[Australian Prime Minister John] Howard can’t lose on this. If he wins, he’ll be wrapped in the Australian flag as protecting the youth of the future. If he loses, then the states [who are his political enemies] get labelled ‘soft on drugs’.”

In the case of marijuana and schizophrenia, the correlation is
something like a two- or three-fold increased risk.

Yet even if most people are not harmed by smoking marijuana – and, as Iversen puts it, “many find it a very useful drug” – there’s no doubt a minority is harmed.

And that minority is recognisable to many. It might be the vulnerable teenager for whom marijuana is the grease that slides them towards aimless drug-dependence; psychiatrists will think of their mentally ill patients whose marijuana habit makes their disease much worse; and then there is that minority in the general population, largely undetectable, who have a predisposition to schizophrenia. Most psychiatrists now believe marijuana smoking will push those susceptible to schizophrenia over the edge.

Just because two things are correlated doesn’t mean one caused the other. For instance: there is a high correlation between the number of people who drown each year and the number who consume ice cream. Does that mean eating ice cream causes drowning? No; it’s just that both events happen more frequently in summer.

In the case of marijuana smoking and developing schizophrenia, one hidden common factor could be a family break-up – a life stress that is known to increase the likelihood of both occurrences. Such factors are called ‘confounders’.

Observational human studies form the backbone of epidemiology, the study of diseases in populations. Yet their attempts to nail a disease to a particular cause are often bedevilled by confounding factors – unless the effect is huge, as it was when researchers noticed a strong correlation between tobacco smoking and lung cancer: smokers were 15 times more likely to develop lung cancer than non-smokers. That’s a big enough difference to identify with certainty a likely real-world effect.

But in the case of marijuana and say, schizophrenia, the correlation is something like a two or three-fold increased risk. “Epidemiologists tell us that a two-fold increased risk is very suspect,” says Iversen. “And it could disappear entirely if we’ve missed any confounding factors.”

The other thing about marijuana science is that the scientific literature is a jungle. As Cohen warned, there are scientific papers that will confirm whichever viewpoint you may care to hold. If you look hard enough, you can find a study that will back almost any hypothesis. The trick is separating the good studies from the mediocre ones.

How strong is the link between marijuana and schizophrenia? Does marijuana make you mad? Certainly some users experience disturbing symptoms. When the 19th century psychiatrist Jacques-Joseph Moreau experimented with hashish – the resinous extract of cannabis – on himself and European artists of the Hashish Club, he reported being able to mimic the entire spectrum of psychiatric disease.

In 1936, the cult movie classic Reefer Madness also reflected the belief that marijuana users became ‘criminally insane’. For most people, marijuana is a lot like alcohol, producing rather more pleasant symptoms, and any ‘madness’ stops once they sober up. What has become a major concern in the last few years is that for some people, the madness doesn’t stop.

The medical term for this form of madness is psychosis. For a psychotic, the line between the imagined and the real world blurs: hallucinations, delusions, irrational thoughts and fears take over.

If marijuana was causing schizophrenia we should see an increased
number of cases ... but the rate has stayed at about 1%.

The full-blown version is schizophrenia. Psychiatrists have long suspected a link between psychosis and marijuana because of what they see with their patients. “It would be unusual to find a psychotic patient who doesn’t use it,” says Judy Bernshaw, a Melbourne psychiatrist who saw patients at a public clinic. The medical papers report around 40-60% of psychotic patients regularly smoke marijuana. And, says Castle, “smoking makes them madder; getting them off it is a major challenge”.

But does marijuana make these patients psychotic … or were they psychotic to begin with? Perhaps psychotic people are simply more attracted to marijuana? With patients, you see an association; but you can’t tell which came first.

To address this, researchers began studies that tracked people over several years. The biggest and the best of these began in the 1970s with some 50,000 Swedish army conscripts. They were interviewed at age 18 about their marijuana use. After 15 years their medical records were checked, and a disturbing finding emerged. Heavy users, who had smoked 50 times or more before enlistment, were up to seven times as likely to have been hospitalised for schizophrenia.

Ganja Faeries dance during Nimbin's Mardi Grass parade protesting marijuana's prohibition. – Peter Ptschelinzew/Lonely Planet Images /Getty Images

On the other hand, only 3% of the heavy users developed the disease. A closer look showed that many had reported symptoms of psychiatric illness (like odd beliefs or hearing voices) at the outset of the study, so might have developed schizophrenia irrespective of smoking.

The researchers re-analysed their data excluding the conscripts with pre-existing symptoms. They still found that heavy marijuana users were three times as likely to develop schizophrenia.

Does this prove marijuana causes schizophrenia? “The jury is still out,” says Iversen. “The problem is that only a small proportion of people smoke heavily, and only a small proportion of people develop schizophrenia – we’re dealing with vanishingly small numbers.”

Given the large increase in the number of people who use marijuana over the past 30 years, as well as its increased potency, if marijuana was causing schizophrenia we should see an increased number of cases. But estimates by Hall and others show that the rate has stayed at about 1%.

Many researchers believe the most plausible explanation of this data is that marijuana does not trigger schizophrenia in those who would otherwise not develop it. Rather, marijuana use brings on symptoms earlier and more severely in patients who would get the disease anyway. Says Castle, “It seems to be the straw that breaks the camel’s back.”

To find out who these susceptible people are, a New Zealand study looked to their genes. The study showed that people who carried a particular variety of a gene called catechol-o-methyl transferase (a gene involved in the synthesis of the brain chemical dopamine), were about 11 times more likely to develop schizophrenia if they used marijuana.

But in most cases of schizophrenia, researchers can’t pinpoint the genes responsible. The best guide as to who is most at risk from smoking marijuana is a family history of mental illness or existing psychotic symptoms.

Marijuana use has also been linked to depression. A 2002 study published in the British Medical Journal by George Patton, of the Centre for Adolescent Health at the University of Melbourne, showed that marijuana use doubled the risk of later depression and anxiety in teenage girls.

Other studies, like a 2005 paper in the journal Addictive Behaviours by Thomas Denson at the University of Southern California and Mitch Earleywine of the University of Albany found the opposite: it was entitled “Decreased depression in marijuana users”. Wayne Hall agrees that the link between marijuana and depression is even more open to question than that between marijuana and psychosis.

As for addiction, the common wisdom is that marijuana is not an addictive drug. The laboratory rat will attest to that: put heroin, cocaine or amphetamines into its water bottle and the rat will keep coming back. Put the main active component of marijuana, THC (delta-9-tetrahydrocannabinol) in its food and it won’t.

Yet, scan through the scientific journals and the academic literature and you’ll find a surprising term: ‘marijuana dependence’.

“Whether or not there is a cannabis dependence syndrome is one of the most contested claims in the cannabis policy debate,” admits Hall.

Addiction is characterised not just by a craving for more or increased physiological tolerance to exposure, but also by withdrawal symptoms.

Adds Paul Dillon, a spokesman for Australia’s National Drug and Alcohol Research Centre (NDARC): “If you talk about a drug of dependence, that heightens attention and the chance that the legal ramifications will be upped. A lot of people simply don’t consider marijuana to be that harmful.”

According to Earleywine, author of the books Understanding Marijuana, and the soon-to-be-published Pot Politics, the changes in terminology – which evolved from ‘physical addiction’ to ‘psychological dependence’ to ‘dependence’ – might have been an attempt to get marijuana labelled as a true drug of addiction.

“The bottom line is that marijuana never quite qualified as such, so they started making distinctions. Nobody ever liked the ‘psychological dependence’ idea, as it was meaningless and [people] started applying it to running and love and everything else. Rumour has it that the whole thing was all about getting marijuana users diagnosed as dependent.”

But addiction is characterised not just by a craving for more or increased physiological tolerance to exposure, but also by withdrawal symptoms. “People were still trying to find marijuana withdrawal after 4,000 years of use,” notes Earleywine.

On the other hand, Hall says that the changing perception of marijuana from a non-addictive drug to a drug of dependence was just a natural consequence of the passage of time. “This is what we saw when cocaine and amphetamines started being used. They weren’t considered addictive drugs. Cannabis is just repeating history.”

For a snapshot of what marijuana dependence actually looks like, take a visit to one of the burgeoning clinics in Britain, the US, Australia and Amsterdam. According to a 2001 study by the Australian Institute of Health and Welfare, the fraction of patients who attended drug clinics for marijuana dependence rose sharply, from 4% to some 21% over 10 years.

“There’s no question that some people get into strife and can’t stop,” says Hall. “A dependent marijuana smoker is like a heavy drinker or smoker: they are chronically intoxicated and spend as much as 25% of their income on it. Often we look at people in their early 30s, who may have smoked daily for 15 years without knowing there was a problem. Then they try to stop, and they can’t. Other typical cases are young boys in juvenile detention or in the mental health service. They smoke 20 to 30 bongs a day, every day.”

Controversial or not, the terminology change does not seem to have been part of a conspiracy to demonise marijuana. In the 1970s, the World Health Organisation pushed for a terminology change to remove the stigma attached to the word ‘addict’. And as new drugs came out of fields and laboratories and into widespread use, the term ‘addiction’ became outdated because it was specifically tailored to the use of heroin and opium (known jointly as opiates). When amphetamines or cocaine came along in the late 1970s, they didn’t fit this description, and so were not considered harmful drugs. Eventually, says Hall, their harmful effects became apparent. And better checklists were required.

Over the past 20 years or so, several checklists have come and gone. The latest and most widely used is the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders, currently in its fourth version and generally abbreviated as DSM IV. This checklist looks at the broad impact of the drug on the person’s life as well as the psychological and physical fallout. For instance, does it disrupt their professional or personal life? Do people use it despite knowing it causes them problems? Do they spend a great amount of time and money trying to get the drug? Do they find it difficult to give up? There are seven items on the checklist; if the user scores three of them in the previous 12 months, they are considered dependent.

On this radar screen, marijuana certainly makes an appearance. According to Hall, about one in 10 people who sample marijuana will become dependent on it. But let’s keep things in perspective: for cigarettes the comparable figure is one in three, for alcohol one in six, and for heroin it’s one in four.

Looked at this way, marijuana is but a minor offender. However, given the large number of marijuana users, the figures start to climb. According to a 2001 study by Wendy Swift at NDARC, an estimated 300,000 Australians are marijuana dependent. Certainly the briefing information for the Australian National Cannabis Strategy, an attempt to come up with a plan for dealing with cannabis that delivered its report in May 2006, describes cannabis as “second only to heroin use in terms of healthy years of life lost … there were more disability-adjusted healthy years of life lost in 1996 due to cannabis use and dependence than [due to] HIV, hepatitis B and hepatitis C.”

Still, according to Earleywine, “that alarming equation smacks of statistical hand waving; a few assumptions turned into an equation that sounds more alarming than it really is. Marijuana withdrawal symptoms are things like irritability and not having the munchies [food cravings]. Of all the things I’d rather have, cannabis dependence is way above those others.” As to the evidence that cannabis causes significant losses of time in employment or in relationships (the so-called ‘amotivational syndrome’), Earleywine contests the data. He cites his own study on a group representing the general population – Internet users – that was published in January 2006 in the journal Substance Abuse Treatment, Prevention, and Policy. It showed that regular marijuana users didn’t necessarily take more sick days or earn less money.

As time has passed, cannabis dependence syndrome has been described not only in humans, but in rats too. In the past, rats were reassuring because they didn’t get addicted to THC when it was added to their food. But according to the traditional rat test, nicotine isn’t addictive either – and anyone who has tried to give up smoking tobacco will certainly disagree with that. So could it be that there’s something wrong with the test?

Just as people are now given a different test to measure dependence, so are rats. If rats are put in a cage with a red and a green room, and they are injected with THC only in the green room, they will end up spending more time in the green room. Arguably, it mimics the behaviour of a dependent person: they change their life activities to acquire the substance. On this test, rats are revealed as forming dependence on both nicotine and cannabis.

A couple of rat studies undertaken in 1997 also led scientists to view cannabis in a more sinister light. Opiates act on the brain’s reward circuitry, which exists to keep us having sex, eating and doing well at tasks. When we do one of those pleasurable things, the brain rewards each of these functions with a hit of dopamine, a naturally produced neurotransmitter.

With food, sex and work, our bodies give us feedback to say when we’ve had enough. But opiates go straight to the brain, to keep activating the pleasure centre. With every hit of heroin, the user gets a hit of dopamine.

If rats are injected with heroin, researchers see surges of dopamine released. In 1997, when researchers at the University of Cagliari in Italy injected THC into rats, they saw a comparable dopamine surge.

'If I knew as much about the mechanism of action of cannabis as I now
know, I would never have touched it 35 years ago.'

For some scientists, studies like this changed their perception of cannabis forever. In a commentary in the US journal, Science, neurobiologist David Friedman at Bowman Gray School of Medicine in North Carolina said, “These studies supply important evidence that cannabis acts on the same neural substrates [brain circuits] and has the same effects as drugs already known to be highly addictive. They send a powerful message that should raise everyone’s awareness about the dangers of cannabis use.”

Henry Lester, a biologist who studies the chemistry of nicotine addiction at the California Institute of Technology, put it this way, “If I knew as much about the mechanism of action of cannabis as I now know, I would never have touched it 35 years ago. I consider it a highly dangerous drug, akin to the opiates.”

Does Marijuana trash your brain? There’s no doubt a youngster smoking a dozen bongs a day is not going to score too well on an IQ test. But what about someone in their 30s or 40s who has smoked a couple of joints each night after work for 10 or 20 years? Once they get off the dope, will their brains recover? And what about the young bong user?

As with everything in the marijuana debate, getting a simple answer is not easy. You can find studies showing that users have a lower IQ: but then, some of these studies don’t take into account the fact that marijuana hangs around in the system for days.

A 2001 study by Harrison Pope and colleagues at the Harvard Medical School and published in the Archives of General Psychiatry showed how critical it was to allow all marijuana to ‘wash out’ from the system before measuring performance. Heavy, long-term users were compared with people who had never used the drug. The long-term users then underwent 28 days without smoking. In the first several days the users scored well below the non-users in various mental tests. By day 28, there was no difference.

Another criticism of such studies is that the IQ difference between the two groups being tested might have nothing to do with marijuana use. One clever study got around this by subtracting each person’s IQ score at age nine from their score at age 20. This study found that past marijuana use made no difference to a person’s IQ.

Iversen reviewed many of these studies for the journal Brain. He found that studies on long-term, very heavy users of cannabis in Jamaica and Costa Rica (those smoking 10 to 20 joints per day for more than 10 years) failed to show any significant difference between users and non-users. Similar negative results were reported in some studies of US college students.

Researchers now believe the brains of teenagers are particularly vulnerable.

On the other hand, he described some studies that showed subtle mental deficits in ex-cannabis users, particularly when it came to discriminating patterns of sounds. In conclusion he wrote, “Such impairments appear to be associated with long-term heavy use of the drug and are unlikely to affect most recreational users.”

More marijuana is being smoked by younger and younger people: according to the 2004 Youth Alcohol and Drug Survey in the Australian state of Victoria, about a quarter of 16- to 24-year-olds had smoked marijuana during the previous year.

This rings alarm bells because researchers now believe the brains of teenagers are particularly vulnerable. The brain is still undergoing a crucial phase of its development during the teenage years. At birth, the 100 billion cells of the human brain (or neurons) are like tiny islands with sparse connections between each other. Over the next seven years, the spaces between them grow thick with tangled connections. And then something extraordinary happens: the connections get pruned back.

This remarkable pruning moves from the part of the brain that deals with instinct and emotion to the centres that engage in rational decision-making. Because the pruning seems to be required for peak function, researchers have speculated that this might explain the sometimes irrational behaviour of teenagers. In other words, the emotional circuits are running at full capacity before the reasoning inputs are finished.

Murat Yucel, a neuropsychologist and brain researcher at the Orygen Research Centre at the University of Melbourne, reads even more into this finding. “We know that 75% of all mental illness has its origins during the teenage years. We’ve been aware of that for a long time, but now we may understand why.

“This is a critical time when parts of the brain involved in weighing up one’s actions are still maturing and connecting up with the emotional centre. Maybe disrupting that link has something to do with the emergence of mental disorders.”

Just as a finished building is better able to withstand damage than the bare foundations, the brains of teenagers are likely to be more vulnerable to the effects of damaging drugs.

Marijuana plants growing indoors under lights. – Fredrik Skold/Getty Images

So far, the evidence incriminating marijuana is sparse, but Yücel sees an intriguing trend: in those who have used both alcohol and marijuana from an early age, the size of the amygdala (where emotions are processed) is larger; while the hippocampus (where short-term memories are stored) is smaller than in people who used the cocktail later in life. Interestingly, that is precisely the kind of problem reported by many drug users: mood disorders and memory problems.

Most of the researchers I interviewed, including Yücel, agreed that it remains to be proven whether marijuana permanently affects the function of the teenage brain. Still, none hesitated to proffer that they thought teenagers were at the highest risk from using marijuana, and should avoid it.

David Castle’s concerns relate not so much to long-term brain damage but the clear-cut impairment to learning and memory. “My concerns are more at a pragmatic level; if youngsters are stoned – and the higher doses today are a major concern – then they are not going to lay down the bedrock of education they need.”

There is also agreement that the younger users were more likely to spiral down into dependence followed by the use of harder drugs, dropping out of school, perhaps falling into crime … indeed, the whole nightmare that spooks parents. It seems no-one is going to be able to prove this one, but the warnings seem clear: delay marijuana use as long as possible. Use it moderately. Don’t use it at all if you have a personal or family history of mental illness. And stop using it if it makes you feel anxious, distressed or paranoid.

Other harms of regular marijuana use include an increased risk of emphysema (destruction of the elastic wall of the air sacs in the lung) above that of smoking alone.

Some studies have shown that it increases the risk of head and neck cancers. And while researchers such as Hall have long been unconvinced about a link between marijuana and lung cancer, in May 2006 researchers at the University of California, Los Angeles reported they found no increased risk of lung cancer in marijuana smokers. Tobacco smoking, however, increased the risk by 20-fold.

Again, to quote visiting Oxford pharmacologist Les Iversen: “On balance, the public health risks are small. Bear in mind that millions of people smoke marijuana occasionally and there is no evidence of harm. You have to judge the benefits against the risks. I would say a lot of people benefit from moderate use. But that’s not to say it’s not a dangerous drug.”

No scientist, clinician or expert I talked to would argue that marijuana is harmless. Where the battle lines are drawn is how that harm can be reduced.

“People only pay attention to the harms of cannabis,” observes Hall. “If they believe it’s harmful, they want it criminalised. If they believe it’s harmless, they want it legalised. But you’ve got to look at both sets of harms – the harms of cannabis and the harms of prohibition.”

The intention of making cannabis illegal is to reduce the harm by reducing its use. But despite the decades of prohibition, cannabis use continues to flourish in the US and elsewhere. In Australia, according to the 2004 National Drug Household Survey, about two million people used cannabis during the previous year; that’s about 10% of the total population. Clearly, cannabis use is entrenched in developed nations like Australia.

Many in the political elite understand the futility of prohibition. Lord Birt, a former director-general of the British Broadcasting Corporation, was commissioned to write a report on illicit drugs for the British cabinet.

In August 2005, the explosive 105-page report was released in response to a freedom of information lawsuit by The Guardian and other newspapers, and promptly posted on its website. It summarised its findings as follows: “The drugs supply market is highly sophisticated. Attempts to intervene have not resulted in sustainable disruption to the market at any level. As a result: i) the supply of drugs has increased; ii) prices are low enough not to deter initiation; iii) but prices are high enough to cause heavy users to commit high levels of crime to fund their habit.”

As an article from the Washington DC-based Drug Reform Coordination Network opined, “it would be hard to sugar-coat the report … With its pointed comments that British drug dealers have higher profit margins than Gucci, Luis Vuitton, and other luxury goods purveyors, and that police would have to intercept up to 80% of drugs entering Britain to affect dealers’ profit margin (seizure rates are 20% at best, the report noted), it is little wonder the Blair government didn’t want the report released.

Its grim conclusion was that even if prohibitionist measures succeeded in driving up prices, the victory would be pyrrhic because problem drug users would commit more crimes to obtain their drugs.”

If we are to believe Lord Birt, prohibition doesn’t work. And there are plenty of compelling arguments that prohibition does harm: cannabis users are stigmatised by a criminal record – although states in Australia mostly issue warnings or fines to users, occasionally they go to jail. They are also exposed to drug pushers, who also peddle highly addictive amphetamines, cocaine and heroin.

There is also the harm caused by having a substance used by millions easily available, without any testing of its strength or quality. Then there is police time and resources trying to enforce a law that a great number of citizens regularly flout. And cannabis prohibition is a notorious driver of police corruption, as four Australian royal commissions since 1986 have all concluded.

Lastly, there is the economic loss to the community. According to Kenneth Clements, an economist at the University of Western Australia, cannabis is a A$5 billion domestic industry – double that of the wine industry. And the community suffers twice as a result of prohibition.

First, they pay the costs of policing cannabis: a 1995 Australian estimate was that 13% of all criminal justice and police resources were devoted to cannabis crime. Second, they are deprived of the benefits of a ‘white market’ economy: regulated legalisation of cannabis would generate taxes that could be returned to health and education.

In June 2005, 500 of America’s ivy league economists, led by Nobel economics laureate Milton Friedman, wrote to US President George W. Bush, calling for an honest debate about marijuana prohibition. “We believe such a debate will favour a regime in which marijuana is legal, taxed and regulated like other goods,” they said. Harvard University economist Jeffrey Miron estimates the regulation of marijuana would produce savings and tax revenue of up to US$14 billion a year.

Alex Wodak too believes marijuana should be taxed and regulated. “There would still be law enforcement, and there should be health warnings and messages like: if you can’t control your use, ring this number. There would have to be proof of age required as well.” Would he advocate this approach for all drugs? “No – cannabis is unique among illicit drugs. It’s the only one where there is a strong case for treating it like alcohol and tobacco. But not like coffee and sugar.”

But this is not the direction in which the political world is moving: when Australia’s long-awaited National Cannabis Strategy was released in May 2006, some researchers and clinicians were bitterly disappointed. The sombre document recast marijuana as a ‘hard’ drug and recommended a three-pronged strategy: cutting off the supply, cutting off the demand, and finding treatments for those with a problem.

With the release of the document, the Australian Parliamentary Secretary for Health, Christopher Pyne, exhorted the nation, “We have to treat it [cannabis] as an illicit drug as dangerous as heroin, amphetamines or cocaine.”

In contrast, the National Alcohol Strategy, released around the same time, had a positively chirpy tone. Its opening paragraph read, “Alcohol plays an important role in the Australian economy. It generates substantial employment, retail activity, export income and tax revenue. Alcohol also has an important social role…”

Nick Walsh, a family doctor at the Turning Point Alcohol and Drug Centre in the state of Victoria, shook his head at the National Cannabis Strategy. “Disappointing, not progressive, but expected. It’s hard not to be cynical and see that this document is trying to fulfil our obligations to the international narcotics control board rather than address the underlying issue that the cannabis industry is unregulated and uncontrollable because it is illegal.”

Hall is less critical: “The Australian federal government would like to recriminalise marijuana, [while] the states are divided. Given the disagreements, this document is a sensible compromise.” Though Hall advocates legalisation of cannabis, he says “there’s a snowball’s chance in hell of that ever getting up.”

As far as law reform or the medical use of marijuana (currently illegal) goes, this was not part of the terms of reference for Australia’s cannabis strategy – the authors were not even permitted to address the issues.

Why do countries such as the US and Australia seem increasingly prohibitive? “In the debate over drug policy, rationality and evidence is a small factor,” says Wodak. “It’s about winning votes by being hard on drugs”, a strategy he dubs “political Viagra” for politicians. Although, he adds, “it’s not as reliable as it used to be.”

A stunning example is the Shafer report. In 1970, then US President Nixon wanted an investigation into marijuana to back his war on drugs. He appointed Raymond Shafer, a Republican former governor of Pennsylvania with a reputation as a ‘drug warrior’ to lead it. Shafer’s committee conducted the most wide-ranging review of marijuana ever undertaken by the US federal government. And Shafer did a complete about face.

In his 1972 report, Marijuana: A Signal of Misunderstanding, he said: “Marijuana’s relative potential for harm to the vast majority of individual users and its actual impact on society does not justify a social policy designed to seek out and firmly punish those who use it.” As Watergate revealed, Nixon was appalled, and waged his war regardless. Since then, 15 million Americans have been arrested on marijuana charges.

Notwithstanding the current hardening of Australia’s cannabis policy, Wodak is surprisingly optimistic. “It’s a winnable battle. The arguments are so compelling. The policy has got to be based on rationality and evidence, not fearmongering and angst.”

Wodak draws some cheer from Britain’s recent decision. In December 2005 Michael Rawlins, the chairman of the UK Advisory Council on the Misuse of Drugs, recommended that the British parliament not upgrade its punitive laws on cannabis from Class C to Class B; a recommendation that was accepted. “While cannabis can, unquestionably, produce harms, these are not of the same order as those of substances within Class B [the more punitive category that includes amphetamines, barbiturates and codeine].” He recommended education programs to discourage use and more research.

Despite his two decades in the trenches, Wodak shows no signs of battle fatigue. “What keeps me going? Every day I see people and their families damaged by these costly and ineffectual and counter-productive drug laws and policy. There is the excessive permissiveness to alcohol – we regularly see women bashed by drunken husbands – while marijuana remains criminalised.

“In thoughtful circles, the debate is over: harm reduction wins. Now the task is to get this through the political maze.”

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