Unfortunately, this debate seems to be filled with a lot of people on both sides saying "Recent research clearly states..." and then not backing that up with any recent research whatsoever! Let us have a look at some recent research.
A clinical trial, for example, is only of any worth when it contains enough people in it to be reasonably sure that the data is representative of a wider population. Even then, there are problems. A trial conducted with three thousand people has less than a one in three chance of picking up on a one in ten thousand adverse drug interaction.
Like all not immediately fatal drugs, the only real assessment of the safety of cannabis is an epidemiological one.
But medicine also learns from case studies. By looking at multiple individual cases, we begin to learn something of the nature of illness. These studies do, however, have to be good, solid, and scientific.
So, seeing as there have been several studies conducted on the epidemiology and medical effects of cannabis, lets have a look to see what they say on the important questions, namely:
(1) is cannabis harmful?
(2) is cannabis addictive?
(3) does cannabis use lead to the use of harder drugs?
Only by answering these questions can we deduce whether this drug ought to be legalised.
Is Cannabis Harmful?
Its hard to imagine that anyone would claim any psychoactive substance might be risk free, so the question is really 'To what extent do we have evidence of the harmful effects of cannabis'.
What do the research papers say on this?
Myocardial and Renal Disease/Infarction
We know from studies such as Mittleman et al. (2001) that taking cannabis can lead to myocardial infarction ('The risk of myocardial infarction onset was elevated 4.8 times over baseline (95% confidence interval, 2.4 to 9.5) in the 60 minutes after marijuana use. The elevated risk rapidly decreased thereafter.'). Note that in this study, it isnt heavy use of the drug that is dangerous, but it is an immediate risk of taking the drug that is being highlighted.
Heavy use of any drug is, of course, dangerous. Lambrecht et al. (1995) identified heavy use of cannabis as a cause of acute renal infarction.
So, in terms of myocardial infarction we can say that cannabis is more harmful than alcohol, but not necessarily more harmful than alcohol. We can also say that heavy users of cannabis can suffer similar kidney problems to alcohol abusers, but it is unclear to what extent this is a problem.
The first thing that one notices when looking at the literature on cannabis and cancer is that there are a hell of a lot more papers discussing this than actually contain any real research work. A lot has been stated on the possibility of using cannabis and derivatives for cancer treatment, or alleviation of symptoms, but that application (the medical use of the drug rather than the recreational) is not the subject of this article.
Marselos and Karamanakos (1999) discuss the fact that cannabinoids promote tumour growth in animals, and ought thus be considered as carcinogens. Li and Lin (1998) have also reviewed the published work in this field, and concur with the findings of Marselos and Karamanakos. Nahas and Latour (1992) demonstrate that cannabis is implicated in oral cancer.
While Jemal et al. (2001) point out that its hard to de-convolute data on lung cancer and cannabis from the effects of tobacco, they also point out that the link between the two certainly cant be refuted from gross epidemiology. Carriot and Sasco (2000) showed that cannabis is implicated in head and neck cancer, reinforcing the earlier findings of Zhang et al. (1999). In light of the findings of Sarafian et al. (1995), who showed that marijuana use causes DNA damage in alveolar macrophages (thus leading to increased chance of lung or throat cancer).
An interesting finding by Sarafian et al. (1999) is that THC in cannabis smoke is a major cause of oxidative stress in cells, and is thus most likely carcinogenic.
Ammenhauser et al. (1998) demonstrated the mutagenicity (hence carcinogen status) of marijuana, and that this drug is implicated in birth defects if used by pregnant women. Sidney et al. (1997) were a more specific, their epidemiological study showing that many cancers may not be affected by cannabis, but some specific forms of cancer may well be.
Cannabis has also been implicated in cancer in many earlier studies, such as Sherman et al. (1995), Caplan (1991) and Ferguson et al. (1989).
It is in my opinion clear that cannabis can cause cancer. It looks more dangerous than alcohol in this respect, although its not clear whether its as dangerous as tobacco.
Caberlotto and Hurd (2001) demonstrated that marijuana use leads to elevated levels of neuropeptides associated with suicide, and that no other drug is associated with this particular peptide. Court, in his 1998 review, concluded that . "There is sound evidence that cannabis intoxication has an adverse effect on cognitive function and behaviour, and may, in Vulnerable individuals, lead to a psychotic reaction. Regular use may have an adverse effect on learning, with possible mid-to long-term psychological and cognitive impairment. Heavy use may lead to emotional dependence with consequent social and psychological dysfunction."
Many studies have found a link between cannabis and schizophrenia, but relatively few have looked for a cause/effect relationship. It is not disputed in any of the literature I can find that cannabis is widely used by patients suffering from this condition, and that the effects of the condition are severely exacerbated.
Johns (2001) showed that the use of marijuana can increase the incidence of schizophrenia, especially in patients prone to the disease. Indeed, the overwhelming view in the scientific literature is not just that cannabis use is associated with schizophrenia, but can be a contributing factor. Skosnik et al. (2001) support this hypothesis, and Dean et al. (2001) suggest a likely neurological mechanism.
Possibly the best data on cannabis and schizophrenia is from Hamrecht and Hafner (2000). This intriguing epidemiological study found that cannabis use was associated with a doubling of incidence of schizophrenia. A slightly earlier study by Hall and Degenhardt concluded that although the evidence for cannabis use causing schizophrenia was unclear, the drug does clearly make symproms worse.
Jentsch et al. (1998) showed that cannabis use can lead to severe cognitive defects.
McGee et al. (2000) showed that while having mental illness at the age of 15 leads to a small increase in prevailance of cannabis use at the age of 18, the use of cannabis at the age of 18 leads to an increase in the likelihood of mental illness at the age of 21.
We can conclude that it looks very likely that cannabis use can increase the likelihood schizophrenia. We can also conclude that this drug makes such conditions worse, and that people with schizophrenia are at an increased risk of suffering further ill effects from using this drug, i.e. cannabis is here demonstrably adversely affecting some of the most vulnerable members of our society.
Other Health Problems
Scragg et al. (2001) demonstrated that maternal cannabis use is implicated in a huge increase in likelihood of sudden death syndrome in infants.
Taylor et al. (2000) demonstrated that even fairly short duration cannabis use can lead to severe respiratory problems.
Is Cannabis Addictive?
It is often stated by those in favour of legalisation of cannabis that the drug is not addictive, while those who speak against legalisation always seem to claim the opposite. Clearly, in any informed debate on the legalisation of the drug this is of vital importance.
One of the most convincing studies is by Fergusson et al. (2000). In this large birth cohort, while most of those who tried cannabis did not become addicted, 10% of the population displayed clear signs of dependence. Chabrol et al. (2000) also reported a high level of dependency amongst users. A large sample of Australians (over 10000) also showed that a proportion of the population displays symptoms of cannabis dependency (Swift et al. 2001).
There seems to be a general acceptance in the literature that cannabis is a substance to which dependence/addiction can occur. Indeed, it is hard to find any serious article that attempts to refute that point. We can conclude that cannabis dependency is a reality, that it is more frequent in the most vulnerable, but we cannot easily compare levels of dependency with those of alcohol or tobacco. One suspects from the epidemiology papers quoted that the level would be somewhere between the two.
Does Cannabis Use Lead To The Use of Other Drugs?
Fergusson and Horwood (2000) showed that regular cannabis users were 140 times more likely to move on to using harder drugs, and that even taking childhood and social factors into account there was still almost a 60 fold increase in the likelihood of taking cannabis.
There is a large amount of literature that supports or denies the gateway hypothesis, from alcohol to tobacco, from alcohol to cannabis, from cannabis to harder drugs, etc.
The only constant in the literature is that the huge increase in likelihood of moving from one drug to another isnt clearly addressed with any numerical study.
One therefore cannot discount the pharmacological gateway theory in the way that so many advocates of cannabis legalisation do, as a concept we must take it seriously.
Legalise it or Not?
Looking through the recent scientific papers on this drug, it's difficult to see any sound reason for legalisation. Some might argue that the current state of affairs isn't working, that as the drug is available despite its ilelgality there's nothing to be gained from keeping it illegal. Conversely, one could argue that there is a lot of car theft, but there is no call for that to be legalised.
The best evidence available shows that this drug is dangerous, especially to those vulnerable to psychiatric disorders. To argue that a legal stamp of approval be given to this drug seems to me to be quite bizzarre.
But the most dangerous aspect of legalising this drug right now is the misconception there is about the dangers of using it. The prevailant popular culture of the moment insists that this drug isn't dangerous, that it isn't harmful. But that, as we can see, is fundamentally wrong. Would not the legalisation of a drug in such a climate of misinformation be a mistake?
The decisions that individuals might make on whether to take the drug or not cannot easily be based upon its real effect in such a climate of misinformation nd ignorance. As long as this is the case, then this isn't even an issue of personal choice or liberty, it's a simple one of safety.
In my opinion, therefore, it would be wrong to legalise (or decriminalise) this drug at present.