Cannabis use disorder
Recent data indicate that the prevalence of Cannabis use disorders (eg, abuse and dependence) in the United States is approximately 3% among the general population and >30% among Cannabis users.16 The availability of increasingly potent forms of Cannabis has been cited as a possible explanation for this rise, despite no change in the prevalence of overall marijuana use between 1991 to 1992 and 2001 to 2002.17 However, while the prevalence of marijuana use disorders has continued to rise—nearly doubling from 2001 to 2002 to 2012 to 2013—this latest increase occurred with a significant increase in overall marijuana use, such that the actual rate of Cannabis use disorders among users seems to have plateaued, despite the continued rise in marijuana potency.16 This discrepancy could be explained if Cannabis users cut back past a specific threshold of increasing potency. However, 2 studies have called into question how effective such titration efforts might be in practice. In one study, Cannabis users who preferred more potent Cannabis inhaled lower volumes of smoke, but did not fully compensate for the increased potency, such that use of HPC still resulted in greater THC exposure.18 Another study found that HPC users rolled less marijuana into their joints but not enough to mitigate the impact of greater potency.19 Therefore, it appears that HPC users typically expose themselves to greater amounts of THC, which could place them at higher risk of addiction.
Although a causal association between increasing Cannabis potency and the rate of substance use disorders among users remains unclear based on epidemiologic studies from the United States, a recent study from the United Kingdom examined the impact of Cannabis potency on dependence.20 This cross-sectional survey found that, although HPC was preferred by users and was rated as offering the “best high,” its use was associated with increasing severity of dependence, especially among young people. The limited available evidence supports a greater risk of Cannabis use disorders with increasing potency.
Based on longitudinal studies published over the past 30 years, it is clear that using Cannabis at a young age (age <15 to 18) increases the risk of developing a psychotic disorder.21 This association appears to be dose-dependent, with studies consistently demonstrating that psychosis risk increases with greater frequency of Cannabis use.22 The accumulated evidence to date is strong enough to view the psychotic potential of Cannabis as a significant public health concern.21
If risk of psychosis is proportional to the amount of Cannabis used as measured by frequency, it follows that this risk might be affected similarly by Cannabis potency. In another paper, I discussed the potential for greater risk of psychosis in the context of medical marijuana and synthetic cannabinoids.23 My colleagues and I also have published case reports describing emerging psychosis among regular Cannabis users after escalating to higher potency medical marijuana24 and a hyperconcentrated form of hash oil known as Cannabis “wax” or “dabs” that contains as much as 90% THC.4 Preliminary anecdotal evidence supports the plausibility of HPC being more psychotoxic than less potent forms.
Several studies from a research group in the United Kingdom, where sinsemilla has increasingly dominated the drug market, likewise have reported that the use of HPC is associated with a greater risk of psychosis. The first of these studies, published in 2009, found that adults hospitalized for first-episode psychosis were more likely to have used HPC than healthy controls.25 Among Cannabis users, HPC use was associated with a 7-fold increased risk of psychosis, with daily HPC use associated with a 12-fold increased risk.
Based on a larger dataset, a second study reported that high-potency, but not low-potency, Cannabis increased the risk of first-episode psychosis with increasing frequency of use.26 Daily users of HPC had a 5-fold higher risk of psychosis compared with those that had never used Cannabis. A third study reported that HPC use and daily Cannabis use were independently associated with an earlier onset of first-episode psychosis, with daily HPC users developing first-episode psychosis an average of 6 years earlier than non-Cannabis users.27 Finally, a prospective study following patients with first-episode psychosis over 2 years found that the greatest risk of relapse—defined by hospital admission caused by exacerbation of psychotic symptoms—was found among self-reported daily users of HPC, while the lowest risk was among those who stopped using Cannabis after their initial psychotic episode.28
The findings from these 4 studies suggest that the increased risk of psychosis with Cannabis is proportional to overall exposure, determined by both frequency of use and Cannabis potency.