Street Lottery

2. Risk Factors



Cannabis and Mental Health

Now that we have established a broader understanding of mental health, we can examine the key risk factors that are present in the consumption of street cannabis. As highlighted earlier, the drug itself is not the only factor to consider when assessing the impact of cannabis on someone’s mental health. There are a host of variables that can make someone more or less susceptible to poor mental health. From underlying poor mental health or predispositions, to polydrug use, cannabis is never impacting on someone’s mental health in isolation.

The focus of this report, however, is on cannabis itself, its major psychoactive and neuroprotective constituents – chiefly the levels of THC and CBD – and the age at which someone starts to consume it. The reason for this is that these are the factors that can be controlled and regulated by the state to lessen the negative impact of cannabis use. They are also areas in which we can give clear and informed educational messages on consumption, allowing consumers to make more informed choices.

Three Key Risk Factors

  • High levels of THC (increased rates of addiction and problematic use)
  • Low levels of CBD (decreased protective mechanisms against addiction and mental health problems including psychosis)
  • Early onset of consumption while the brain is developing; consuming before the age of 20

Cannabis with a high level of THC and very little CBD, that is used by young people, would therefore present the highest risk.

This research presents an interesting comparison between high potency THC cannabis and Hash.

1. The Protective nature of CBD

A study conducted by Professor of Psychiatric Research, Sir Robin Murray, of King’s College London suggests that individuals smoking street cannabis every day are five times more likely to develop psychosis. The study looked at the association between the consumption of high THC cannabis and psychosis by interviewing 410 south London hospital patients diagnosed with first time psychosis. The research found that those who had used mostly ‘Skunk’-like (high potency THC) cannabis were twice as likely to be diagnosed with a psychotic disorder if they had used it less than once per week, nearly three times more likely if they used it at weekends, and five times more likely if they used it every day.1 The same was not true for Hash, which did not appear to increase the risk regardless of the amount smoked.

This research presents an interesting comparison between high potency THC cannabis and Hash. While both are forms of cannabis, one typically contains far more THC and less CBD – the result of which looks to significantly increase the risk of psychosis.

‘..use of high-potency cannabis (Skunk) confers an increased risk of psychosis compared with traditional low-potency cannabis (Hash)’ – Murray et al.

The reasons for this differential risk level could be that cannabis with high levels of THC has a more harmful effect on a consumer’s mental health. Research has been conducted into the effects of THC which, when administered intravenously, can create psychotic symptoms increasing in severity with the dose.2 This would suggest that cannabis with high levels of THC is the most problematic in terms of increasing the risk of psychosis and such a risk increases with the amount someone is consuming.

The other key factor at play could be the interaction of CBD, as the study stated it was ‘Skunk’ (high THC / low CBD) which carried the most risk. The study suggests that ‘Skunk’ has a high level of THC and next to no CBD. Strains can vary widely in terms of their THC content, which is why we recommend the term ‘street cannabis’. Regardless, the report draws the conclusion that ‘Skunk’ or street cannabis has little to no CBD and high levels of THC.

Research exploring the effect of CBD in cannabis has shown that, when it is administered alongside THC, it can significantly reduce problematic effects both cognitively and psychologically.

‘cannabidiol (CBD) ameliorates the psychotogenic effect of THC and might even have antipsychotic properties. The presence of cannabidiol might explain our results, which showed that hash users do not have any increase in risk of psychotic disorders compared with non-users, irrespective of their frequency of use.’ – Murray et al.

The study acknowledged some limitations in the data, as the readily available high-strength THC cannabis in south London might have resulted in an over-representation of the general population. The study also notes that it did not explore how much cannabis was being used by participants, which means that we cannot be sure how much THC was being consumed.

Research exploring the effect of CBD in cannabis has shown that, when it is administered alongside THC, it can significantly reduce problematic effects both cognitively and psychologically.3 When administered in isolation, THC can induce cognitive impairment and psychotic-like symptoms, but when given alongside CBD, research has shown that these effects significantly diminish.4 In a study carried out by Karniol et al, volunteers were given either a high dose of THC or both THC and CBD together. Those who received both THC and CBD together found the psychological reaction of THC to be significantly reduced.5 A hair sample study by Morgan et al also showed a similar link between THC and CBD, finding that those who tested positive for both THC and CBD in their hair had far fewer psychotic-like effects, than those who tested positive just for THC.6

While research suggests that increasing the level of CBD in cannabis reduces the problematic effects of THC, it does not seem to impact on the feeling of being ‘stoned’ or high from cannabis. Multiple studies have shown that high doses of CBD do not change the experience or pleasurable effects of THC.7 This suggests that CBD is simply protective in nature and does not detract from the pleasurable experience of smoking cannabis.

In an unregulated market, the level of CBD in cannabis cannot be controlled. Furthermore, the harm reduction message that CBD appears to be protective and mitigates against a problematic experience is absent from the procurement of cannabis.

Anecdotal evidence from consumers of cannabis also suggests that CBD plays a key role in moderating the harmful effects of THC and reducing problematic experiences.

“In my experience I have found that when taking CBD alongside cannabis with high levels of THC it has not only reduced my overall level of consumption, but the problematic side effects such as anxiety or paranoia.” – Jonathan Liebling, Political Director UPA

There is, however, further research to be carried out on CBD to establish, in more detail, at what ratio the protective element comes into play. Although academic studies suggest CBD is protective, we do not know at what point this takes place and how research carried out in this area can be practically applied to consumers of cannabis.8

2. THC and Addiction

While most academic research has focused on cannabis and psychosis, addiction is a far more prevalent issue among those who consume it.9 Curran et al estimated that cannabis consumers are nine times more likely to become addicted to cannabis than experience psychosis.10 Although addiction remains a debated term, Curran et al. recognised it to be the “ongoing and compulsive consumption of a substance, despite clear negative consequences to doing so”.11 To better understand the implications of cannabis addiction, the Diagnostic and Statistical Manual for Mental Disorders fifth edition (DSM-5) is a good point of reference. The DSM-5 amalgamated the terms cannabis abuse and cannabis dependence into cannabis use disorder and provided the below symptoms.

DSM-5 definition of cannabis use disorder

  • Cannabis is often taken in larger amounts or over a longer period than was intended.
  • There is a persistent desire or unsuccessful efforts to cut down or control cannabis use.
  • A great deal of time is spent in activities necessary to obtain cannabis, consume cannabis, or recover from its effects.
  • Important social, occupational, or recreational activities are given up or reduced because of cannabis consumption.
  • Cannabis consumption is continued despite knowledge of having a persistent or recurrent physical or psychological problem that is likely to have been caused or exacerbated by cannabis.
  • Tolerance, as defined by either a need for markedly increased cannabis to achieve intoxication or a desired effect or a markedly diminished effect with continued consumption of the same amount of the substance.
  • Withdrawal, as manifested by either the characteristic withdrawal syndrome for cannabis or cannabis is taken to relieve or avoid withdrawal symptoms.12

These conditions are commonplace with those who consume cannabis problematically. A key contributing factor in their development could be the consumer’s exposure to THC. Freeman and Winstock carried out research examining the relationship between cannabis with high levels of THC and dependency. They found that cannabis with high levels of THC is associated with ‘an increased severity of dependence, especially in young people’.13 They also noted that cannabis with high levels of THC was the preferred choice of young people, with participants reporting that it produced the best high. However, it was also associated with stronger memory impairment and paranoia.14

CBD appears, both from academic research and consumer anecdotes, to reduce the problematic side effects of THC and create a more balanced experience.

As THC produces the desirable effects of cannabis, a higher dose can create a strong compulsion to consume again, which is likely to be the reason why a correlation between dosage and dependency is observed.15 If someone is consuming cannabis problematically for the pleasurable experience of THC, then it is understandable that cannabis which provides this to a greater extent becomes more appealing to use.

Research by Freeman et al suggests that those who smoke cannabis with low levels of CBD are more prone to consuming it problematically, and that CBD could act as a protective agent against dependency.16 It could also, according to work carried out by Crippa et al., reduce symptoms of cannabis withdrawal.17

CBD appears, both from academic research and consumer anecdotes, to reduce the problematic side effects of THC and create a more balanced experience. The drug itself is used in isolation to reduce anxiety and improve people’s psychological wellbeing around the world. We need to understand cannabis as a drug that can take many forms, some more harmful than others. The evidence suggests that CBD could be key in reducing this harm. The illicit cannabis market has no obligation to care for the health or wellbeing of its consumers and provides them with no choice.

3. Cannabis and Young People

Due to the way in which brains develop and grow, young people could be at an increased risk of the harmful side effects of cannabis. Research on young people’s consumption of cannabis suggests that, the earlier the onset of cannabis consumption, the more likely they are to experience problematic effects.

Dragt et al. in their study, ‘Cannabis use and age at onset of symptoms in subjects at clinical high risk for psychosis’, concluded that “younger age of onset of cannabis consumption is associated with earlier symptoms of anxiety, social withdrawal, derealization, memory impairment, and difficulties in concentration, with effects being more pronounced in patients with heavier cannabis use.”18

As the brain is growing, regular cannabis consumption impairs its development and maturation.19 The result of this could be that the young person is more susceptible to a mental health problem and issues with cognition. Research carried out by the Centre for Brain Health at Texas University found that earlier consumption of cannabis results in slower brain development in the prefrontal cortex, which is responsible for judgment, reasoning and complex thinking.20 Interestingly, those who began consuming cannabis after the age of 16 experienced the opposite effect, in that their brains showed signs of accelerated ageing.

“In the early onset group, we found that how many times an individual uses and the amount of marijuana used strongly relates to the degree to which brain development does not follow the normal pruning pattern. The effects observed were above and beyond effects related to alcohol use and age. These findings are in line with the current literature that suggest that cannabis use during adolescence can have long-term consequences.” – Francesca Filey, lead researcher

Research carried out by the University of Montreal supports this by showing that young people consuming cannabis before the age of 17 experience brain impairment in the areas of verbal IQ and specific cognitive related activities, all of which occur in the frontal cortex.21 In the study, participants who smoked cannabis before turning 14 performed worse by 20 points on cognitive tests and were more likely to drop out of school earlier.22 The research noted that underperformance in verbal abilities might actually be due to the social implications rather than neurological effects.

“The results of this study suggest that the effects of cannabis use on verbal intelligence are explained not by neurotoxic effects on the brain, but rather by a possible social mechanism. Adolescents who use cannabis are less likely to attend school and graduate, which may then have an impact on the opportunities to further develop verbal intelligence.” – Castellanos Ryan, lead researcher23

It is important to understand this ‘window of vulnerability’ both socially and biologically. The research outlined above highlights how cannabis can impair brain development in young people, but the social factors and lifestyle choices it results in can also play a key role. Young people who are consuming cannabis are less likely to engage in systems of education and, as Castellanos Ryan states, this results in reduced opportunities to develop. The lifestyle that comes with consuming substances from an early age limits educational growth via reduced engagement in school, with young people then becoming isolated from opportunities for development. Those who work on the frontline of drug treatment also find this same link.

“The kids I have worked with in school who smoke loads of cannabis nearly always struggle to engage in education. They become less interested, can’t really be bothered with the lessons and say that the work is becoming too hard. Eventually it becomes a vicious cycle in which they just can’t keep up with the work and don’t believe in themselves anymore.” – Becky, young people’s substance misuse worker, North Yorkshire.

Young people are at an increased risk from smoking cannabis, both biologically and socially. There appears to be an evidence base to suggest early consumption of cannabis is detrimental to the brain, and that the lifestyle choice that comes with cannabis results in decreased opportunities to develop. While this relationship is complex and young people who are socially disengaged may be more likely to consume illicit drugs,24 cannabis is clearly not increasing their chances or potential for growth. The research highlighted in this report suggests that the most vulnerable age group of cannabis smokers are those under the age of 20 who should still be engaged in systems of education.25 Young people in the UK currently have easy access to a strain of cannabis which appears to carry the highest risk.


In this chapter, we have shown how three key risk factors are present in the use of street cannabis in the UK. The evidence indicates that cannabis containing little to no CBD presents the highest risk, and is more likely to induce the problematic side effects of THC. CBD seems to provide an element of protection, without compromising the pleasurable effects of THC. While further research does need to be done on CBD, the evidence and experience cited from consumers indicates its protective nature should be taken very seriously. The illicit market is not focused on the health and wellbeing of the consumer and the consequences of this are deeply problematic.

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