Scientific Consensus and Cannabis Laws

Natércia Rodrigues examines the science behind our current policy regarding cannabis usage.

Discount Medical Marijuana cannabis shop at 970 Lincoln Street, Denver, Colorado. [O'Dea, Wikimedia Commons]


In the UK, it is a criminal offence to either produce, sell, possess or consume cannabis.1 In Portugal, possessing cannabis for personal use is an administrative, rather than a criminal offence.2

Since the first recorded medicinal use of cannabis in 2737 B.C.3 4 but with the Marijuana Tax Act of 1937 possession or transfer of cannabis was strictly prohibited.5 The counterculture of the 1960s brought with it a new perspective on drug use (we’ve all heard of Woodstock ’69).6 This raised awareness eventually culminated in the 1972 report from the National Commission on Marihuana and Drug Abuse (US), entitled “Marihuana: A Signal of Misunderstanding”, in which Richard M. Nixon encourages the ending of cannabis prohibition. Today, most states in the US have either legalised or decriminalised the use of cannabis, both medical and recreational.

In the UK, however, while the pressure for cannabis law reform continues to build, governments have so far shown little flexibility. Only last year, a petition asking for the legalisation of “production, sale and use of cannabis” collected more than 230,000 signatures. In response, and despite the pro-cannabis position of some of the main political parties in the UK parliament,7 the government has claimed that “substantial scientific evidence shows cannabis is a harmful drug that can damage human health” and that “there are no plans to legalise cannabis”.8

“either cannabis causes schizophrenia or it cures cancer…”

Cannabis indica fluid extract, American Druggists Syndicate, pre-1937. [Wikimedia Commons]

Cannabis indica fluid extract, American Druggists Syndicate, pre-1937. [Wikimedia Commons]

This petition claims that cannabis is “a substance that is safer than alcohol, and has many uses”. This marked discrepancy regarding the perceived safety of cannabis use extends not only to politics, but to the media and, consequently, public opinion. Stories published on this topic tend to adopt extreme approaches to it: either cannabis causes schizophrenia9 or it cures cancer, as one news website wrote in separate articles.10 It can be difficult to find clear, conclusive information on the risks and benefits of cannabis, especially with such skewed views on the issue. The lack of unbiased information also hinders our ability to successfully compare cannabis to other substances, like alcohol and tobacco, and decide if the benefits of consumption outweigh the risks.

The truth is that, despite the existence of several studies on the effects of cannabis use on human health, there is no scientific consensus regarding the subject. First of all, it is important to keep in mind that ‘cannabis’ is a genus of flowering plants, including numerous species. These have then been bred to increase potency, as with skunk, and thus the associated risk.

While the main psychoactive agent in cannabis is known to be tetrahydrocannabinol (THC), there are many other agents, the effects of which are largely unknown. These psychoactive agents exist in various amounts in each different strain of the drug, and the effects of their consumption will vary accordingly.

The method of administration is another important factor. Some studies associate cannabis with risk of respiratory and cardiovascular problems,11 but these are mostly associated with the smoking of cannabis; alternative routes of administration – pills, tea, food – could reduce or even eliminate these risks.

Further difficulties arise from the very nature of this type of research: since we are dealing with the effects of a substance in humans, we have to rely on self-reporting. This automatically introduces errors to the experiment; it relies on people honestly reporting their cannabis use, and accurately detailing dosage, frequency, strain and route of administration.

“cannabis may well provide some further treatment options to serious medical conditions for which we currently have no cure…”

From a scientific point of view, when someone takes cannabis the cannabinoid psychoactive agents will successfully bind to receptors in areas of the brain affecting motor activity, coordination, short-term memory, cognition, appetite and pain.12 As anyone who has ever had cannabis can attest to, what that translates to is a feeling of being high – loss of coordination, unusual laughter, blood shot eyes and the munchies. But cannabis also induces mood changes: increased sociability and reduced anxiety or, on the other side of the spectrum, panic attacks, paranoia and psychosis.13 14

This leads into one of the big questions of this discussion – does cannabis cause depression/anxiety/schizophrenia?

Before going any further, it is important to clearly separate causality and association. The observation that people who smoke cannabis are likely to also suffer from depression15 does not prove it is cannabis that causes the depression (causality). It may be that depression makes people turn to such drugs (association).

A dried flower bud of the Cannabis plant. [Evan Amos: Wikimedia Commons]

A dried flower bud of the Cannabis plant. [Evan Amos: Wikimedia Commons]

In the case of schizophrenia, studies suggest that cannabis may have a causal role, but only for chronic users (large doses) and particularly adolescents and people with a history of mental disorder.16 In general, it is thought that even prolonged, regular use by healthy adults does not result in any neurological damage,17 something alcohol has been found to cause.18

“is governmental funding introducing bias in scientific research?”

Meanwhile, the psychoactive properties of cannabis have been looked into as a potential treatment for Alzheimer’s, and several studies have found it to be a promising therapy, worthy of further research.19 20 21 For both Parkinson’s disease and multiple sclerosis, cannabis can help on a more palliative level; a spray inside the mouth has been shown to alleviate pain, reduce sleep disturbance and control painful muscle spasms. In turn, this increases mobility and improves the patients’ quality of life. Administration of THC and other cannabinoids in animal models have been shown to induce cancer cell death and inhibit the process by which tumours build their own network of blood vessels, allowing them to survive. Sadly, previous trials success in animal models have not always translated to humans. It is clear that cannabis may well provide some further treatment options to serious medical conditions for which we currently have no cure. In a country where cannabis is illegal a doctor cannot by any means prescribe it, even if it may be the best treatment for that particular patient.

It is worth considering the possibility of both personal, funding and even contextual bias. A scientist who believes cannabis should be legalised, or is being funded by an organization that does, might undergo studies targeted at finding its benefits, while someone who is against legalisation might focus on its risks. This will then result in two reports, one at each end of the spectrum, neither providing the full picture. It is interesting to notice that, from the references used for this article, the ones published in British journals – where cannabis is illegal – tend to be more critical towards the drug, while the ones published in American journals tend to focus more on its benefits. It raises the question: is governmental funding introducing bias in scientific research?

Despite the obvious need for further research, the medicinal benefits of cannabis and the risks of its chronic, uncontrolled use, are reasonably well reported in the literature. Similar information is available for other substances, such as alcohol or tobacco, and while their purchase and consumption are subject to certain restrictions, mostly on age of sale, they are still legal and widely sold across the UK.

It could very easily be argued that tobacco, which has no health benefits, but is responsible for approximately 90% of lung cancer cases,22 over 30,000 deaths annually in the UK alone, should be banned on public health grounds.

It would seem, then, that as much as scientific knowledge may help well informed policy decisions, the final word lies with public opinion. Even though the current data still leaves the safety of recreational use of cannabis open to discussion, the reported benefits of its controlled medicinal applications should at least allow for some flexibility when considering legalisation for these purposes.


Natércia Rodrigues is currently studying for a PhD in Physical Chemistry.



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