Recent studies indicate that smoking cannabis at a young age can increase the risk of developing schizophrenia by 300 per cent, writes Nadine O'Regan.
'Taking drugs is as normal as having a cup of tea." When Noel Gallagher of Oasis made that comment in 1997, he was condemned as "irresponsible". Anti-drug campaigners vociferously expressed their outrage and journalists breathlessly debated the fallout in article after article.
These days, at least in terms of cannabis-smoking, the validity of Gallagher's statement cannot be denied. More than 20 million Americans use cannabis every year, as do one in 10 British adults. Ireland is not lagging far behind. According to the most recent report from The National Health & Lifestyle Surveys, published in April, 12 per cent of Irish men and 7 per cent of women smoked cannabis in the past year. Among schoolchildren, usage was almost as common, with11 per cent reported having taken the drug in the past year.
The short-term effects of cannabis are well known, but what about the long-term? According to Dr Stanley Zammit, a psychiatrist and researcher at the University of Wales College of Medicine, the information we have gleaned over the past few decades is now almost certainly outdated.
"The drug is much stronger these days," Dr Zammit explains. "In 1969, joints were fairly weak in terms of the active component of cannabis. They contained about 10mg of the active ingredient THC per joint. Nowadays, joints contain up to 150mgs per joint. That's a big problem."
Dr Zammit should know. He recently headed a study, funded by the British Medical Research Council, which examined cannabis usage among 50,000 Swedish military conscripts over a period of 27 years. The study determined that conscripts who smoked cannabis more than 50 times before the age of 18 had a 300 per cent increased risk of developing schizophrenia, compared with non-cannabis users. This risk was dose-dependent. If cannabis wasn't used, the researchers estimated, as many as one in seven cases of schizophrenia could be prevented.
Why cannabis and schizophrenia should be so closely linked is not yet fully understood, but recent investigations suggest that the way in which cannabis acts on the brain has parallels with the changes that take place in the brains of people with schizophrenia.
Scientists from the University of Melbourne's Mental Health Research Institute have discovered that people with schizophrenia have more receptor areas in their brain for delta-9 tetrahydrocannabinol (THC), the primary active component in cannabis and marijuana - a finding which indicates people with schizophrenia may be inherently more susceptible to the effects of cannabis use.
But whether cannabis use causes schizophrenia or whether having schizophrenia simply makes one more likely to smoke cannabis is still being debated. Although Zammit's team took many variables into account and adjusted their findings accordingly, the potential for unknown factors influencing their study meant they couldn't establish a definitive cause-and-effect relationship between cannabis and schizophrenia.
John Saunders, director of Schizophrenia Ireland, believes the drug may make schizophrenia manifest in people who already have a genetic predisposition to the disorder.
"People who have any risk factor for schizophrenia should never indulge in cannabis use," he says. "We've had an increased number of reports of people who are taking cannabis and reporting adverse side-effects, which are like a psychosis. We've also had a number of incidents where people who were diagnosed with schizophrenia have used cannabis over a prolonged period of time, and have suffered relapses and become unstable. The general consensus would be that if you have a diagnosis of schizophrenia or severe depression, you should not use cannabis."
According to a recent Australian study, young people would also be well advised to steer clear of cannabis. Researchers at the Murdoch Children's Research Institute, Victoria, collected data from 1,601 students in 44 schools across the state over a seven-year period. They found that girls who used cannabis on a daily basis were five times more likely to subsequently suffer from depression and anxiety than non-users. Girls who used cannabis weekly had double the risk of incurring depression and anxiety.
In a third international study, headed in the UK by Dr Louise Arseneault, it was discovered that people who had begun using cannabis by the age of 15 were four times more likely than their non-cannabis-smoking peers to be diagnosed with schizophreniform disorders (a type of schizophrenia) in adulthood.
Dr Arseneault gives several reasons as to why this might be the case.
"During the early teenage years, the brain is still developing, and it might be that the effect of cannabis on the brain is much more severe than into adulthood. It could also be due to the fact that when you start smoking cannabis from an early age you're more likely to become dependent on it, and throughout your life you'll smoke cannabis very heavily, as opposed to someone who starts later in life." The drug myths that abound in schools, meanwhile, serve to draw students towards experimentation with cannabis. According to surveys conducted in 2002, 79 per cent of British schoolchildren believe cannabis is "safe". Only 2 per cent feel there are health risks connected with the drug.
"The nature of adolescence is that adolescents will experiment," says Tony Geoghegan, director of the Merchants' Quay Project, Dublin. "But this is the most dangerous period for them because they don't know much about drugs. A lot of their information is misinformation that's gleaned in a shady setting. They're more at risk."
Dr Arseneault agrees: "Reports published recently showed that 30 per cent of people in \ schools are using cannabis regularly now," she says. "This is scary when you consider that they're more at risk of developing psychosis later in life. Policy makers should focus on educating the young people to at least wait; the risk is a lot smaller when you wait. This is not a drug for young people." Both Dr Arseneault and Dr Zammit emphasise, however, that they are not adopting, via their research findings, absolutist positions on the use of cannabis.
"I do not disagree with the studies which show great outcomes for cancer patients who use cannabis," Dr Arseneault says. "I'm not saying that cannabis does not improve their situation. Our study is very specific in finding that people should be concerned about early cannabis use. But it's important to mention as well that cannabis use seems to be all right for a majority of young people. Only a minority will experience a harmful outcome."
Although both researchers decline to comment on the issue of drug legalisation, they agree more investigations are needed into the effects of cannabis use. Up until now, both research and public debate has focused on harder drugs such as heroin and cocaine. Cannabis has fallen between stools - neither damaging enough to be thought worthy of serious investigation, nor legal in sufficient numbers of countries to be granted the same attention as tobacco or alcohol.
But in light of the decriminalisation of cannabis that has taken place in some countries, and the more disturbing effects of cannabis that we do know about, it seems obvious that further exploration into this area is required. Dr Zammit believes that cannabis deserves even more attention than other drugs.
"It should be the more commonly used drugs that get priority," he says, "because even if harder drugs carry an increased risk, if more of your population is exposed to cannabis then that's where your research should focus.
"There are still a lot of questions that we don't know the answers to."