Getting the Straight Dope on Weed

In this guest post, UK PHD student Camilla d'Angelo seeks to demystify the most popular drug in the world, noting that it does have benefits...but it has harms too.

Cannabis is by far the world's most popular illegal drug. Mostly sought after for its mood-altering properties, its effects are varied, ranging from relaxation and euphoria to changes in perception and awareness. The last decade or so has seen an increase in the prevalence of high strength ‘skunk' cannabis, a type of strong herbal cannabis. Skunk-type cannabis is very different from traditional cannabis resin, with evidence suggesting it is also more harmful. Key research comparing different types of cannabis suggests that specific chemicals in the plant are to blame.

At least 70 different cannabinoids are found in cannabis, each having different effects. The principal active ingredient is delta-9-tetrahydrocannabinol-or THC-and is responsible for the ‘stoned' feeling most users seek. Less well known is cannabidiol (CBD), the second major component found in cannabis. The relative ratio of these two chemicals varies greatly between cannabis strains, and it turns out that the CBD to THC ratio strongly influences the high you feel. This is because while THC is responsible for many of the positive effects of cannabis, it can also induce psychosis-like effects such as anxiety and paranoid delusions. CBD, on the other hand, acts as an anti-psychotic, reduces anxiety and has neuroprotective properties. Smoking cannabis varieties that contain more CBD actually modulates the effects of THC and might protect users from the chronic psychotic-like effects of THC.

Over the last 20 years, the constituents of street cannabis have changed drastically, with increasingly high THC strains dominating the market. Whereas the THC content in traditional herbal types rarely exceeds 9%, skunk in the UK can sometimes contain up to 18% THC [pdf]. In addition, skunk-type cannabis, which is increasingly prevalent in Britain today, contains little or no CBD, unlike traditional resin and herbal varieties of cannabis that are more balanced in their CBD to THC ratio. The increasing prevalence of skunk has implications for public health, especially given the association between heavy use of skunk with psychosis and schizophrenia. It is thought that the method of growing cannabis under 24-hour lighting conditions in hydroponic solutions, in a nutrient solution rather than in soil, is responsible for the change in potency. Ironically, then, it is the illegality of cannabis that has made it more harmful.

Following on from last year's controversial programme, Drugs Live: The Ecstasy Trial, which attracted around 2 million viewers, the British television station Channel 4 has announced plans for a new programme that will look into the effects and dangers of skunk cannabis. Two leading psychopharmacologists, Valerie Curran from University College London and David Nutt from Imperial College London, will demonstrate how skunk and traditional cannabis produce different effects on brain and behaviour. Several previous studies by Val Curran and her group have already demonstrated how CBD protects against the harmful cognitive impairing and psychosis-like effects of THC. In one study, 134 cannabis users were asked to remember a piece of text, once when they were stoned and another time when they were sober. Users who smoked cannabis low in CBD content were worse at remembering the text than the high CBD group, suggesting that higher levels of CBD protect against the memory impairing effects of THC.

In another related study, Curran and colleagues found that the ratio of CBD to THC also influences the risk of addiction to cannabis. This is particularly relevant considering the widespread use of skunk in Britain today and evidence that cannabis dependence has increased in the last 20 years, in line with a change in its constituents. In the study, participants were presented with food or cannabis-related cues (photos of joints, cannabis leaves) and assessed for any bias towards either, once when stoned and another time when sober. Bias towards drug-related cues over natural rewards such as food is a hallmark of addiction. The researchers found that smokers of low CBD strains were more biased towards cannabis-related cues compared to users of higher CBD strains, who showed no bias at all. This suggests that CBD acts to modulate the dependence forming properties of THC.

This research helps to shed light on how current drug laws do not necessarily protect users from the dangers of drugs. Ironically, it demonstrates how it is in fact the illegality of cannabis that has increased its potential to harm. In recent years, a growing sense that current drug policies are not working has led to shifting attitudes towards illegal drugs and the relaxation of cannabis laws around the world. Although highly controversial, the benefits of medicinal cannabis have been recognised for some time, with cannabinoid drugs already being used in various countries for pain relief, control of chemotherapy-induced nausea and vomiting, as well as appetite stimulation in AIDS wasting syndrome. In November 2012, voters in the US states of Washington and Colorado passed measures to legalise the recreational use of cannabis. Now, Uruguay is set to become the world's first "green country" as it prepares to legalise the cultivation and distribution of cannabis. Although we should remain cautious, these moves acknowledge that the answer does not lie in prohibition.

No drug is free of harms. But the question of whether it is harmful is less important than the question of how the legal status might reduce or increase those harms.

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Camilla d'Angelo is a PhD student in Experimental Psychology at the University of Cambridge, studying the neural mechanisms of compulsive behaviour.

Image Credit: Cannabis plant by Cannabis Training University