Characterising heterogeneity in the use of different cannabis products : latent class analysis with 55 000 people who use cannabis and associations with severity of cannabis dependence
Sam Craft, Adam Winstock, Jason Ferris, Clare Mackie, Michael T. Lynskey and Tom P. Freeman
Psychological Medicine, 2019, 1–10.
doi : 10.1017/S0033291719002460
Background. As new cannabis products and administration methods proliferate, patterns of use are becoming increasingly heterogeneous. However, few studies have explored different profiles of cannabis use and their association with problematic use.
Methods. Latent class analysis (LCA) was used to identify subgroups of past-year cannabis users endorsing distinct patterns of use from a large international sample (n = 55 240). Past-12-months use of six different cannabis types (sinsemilla, herbal, hashish, concentrates, kief, edibles) were used as latent class indicators. Participants also reported the frequency and amount of cannabis used, whether they had ever received a mental health disorder diagnosis and their cannabis dependence severity via the Severity of Dependence Scale (SDS).
Results. LCA identified seven distinct classes of cannabis use, characterised by high probabilities of using: sinsemilla & herbal (30.3% of the sample); sinsemilla, herbal & hashish (20.4%); herbal (18.4%); hashish & herbal (18.8%); all types (5.7%); edibles & herbal (4.6%) and concentrates & sinsemilla (1.7%). Relative to the herbal class, classes characterised by sinsemilla and/or hashish use had increased dependence severity. By contrast, the classes characterised by concentrates use did not show strong associations with cannabis dependence but reported greater rates of ever receiving a mental health disorder diagnosis.
Conclusions. The identification of these distinct classes underscores heterogeneity among cannabis use behaviours and provides novel insight into their different associations with addiction and mental health.
Key words : Cannabis dependence; hashish; latent class analysis: cannabis concentrates; patterns of cannabis use; sinsemilla
The legal status of cannabis is evolving as many national and subnational jurisdictions legalise or decriminalise its use for medicinal and/or recreational purposes (Hall and Lynskey, 2016; Freeman et al., 2019). Within this dynamic legal landscape, the way people are using cannabis is also changing. In both licit and illicit markets, individuals now have access to a wide variety of cannabis products and methods of administration (UNODC, 2018; EMCDDA, 2019), resulting in novel trends in patterns of use and consumption practices (Borodovsky et al., 2016; Meacham et al., 2018; Spindle et al., 2019).
Cannabis products are typically classified according to their preparation, cultivation process and the content of two cannabinoids – tetrahydrocannabinol (THC) and cannabidiol (CBD). THC concentration is often referred to as a measure of potency (i.e. percentage of total weight), and produces the reinforcing effects of cannabis as well as the transient negative effects (Curran et al., 2016). By contrast, CBD is non intoxicating at doses typically found in cannabis products and has been shown to offset some of THC’s negative effects (Englund et al., 2013) without altering the reinforcing effects (Haney et al., 2016). THC and CBD are synthesised by the cannabis plant in glandular trichomes, which appear most abundantly on the flowers of female plants – therefore these glandular trichomes are typically harvested for cannabis production (Potter, 2014).
In its traditional form, herbal cannabis consists of seeded floral material, usually dried and dark green to brown in colour. Derived from outdoor-grown landrace (domesticated, locally adapted, traditional variety) plants, THC concentrations in these products are typically modest; around 6% in the US (Chandra et al., 2019) and 9% in the U.K. (Potter et al., 2018). Alternatively, high potency herbal cannabis (referred to here as sinsemilla, meaning without seeds) is produced from intensely cultivated indoor grown plants, which have been selectively bred for their THC yield and prevented from fertilisation to increase THC synthesis (Potter, 2014). As a result, this variety is much more potent than traditional herbal cannabis (∼17%) – though there is considerable variation within and between countries (Chandra et al., 2019; EMCDDA, 2019) – and their growing market dominance is contributing to the rise in potency of the cannabis currently being used in many parts of the world (Zamengo et al., 2015; Potter et al., 2018; Freeman et al., 2018a; Chandra et al., 2019). Cannabis resin (i.e. hashish) is sold in compressed blocks of extracted plant trichomes. Unlike herbal cannabis or sinsemilla – which are typically devoid of CBD – hashish is traditionally characterised by similar proportions of both THC and CBD (in the U.K ∼5%; Hardwick and King, 2008). However, the cannabinoid profiles of these products are determined by the plants used to produce them. Recently, THC concentrations have been increasing substantially with potencies reaching 15–20% throughout Europe (Freeman et al., 2018a), USA (Chandra et al., 2019) and Morocco (Stambouli et al., 2016) – a major producer for illegal export to Europe and other north African countries (EMCDDA, 2019).
These most common varieties of cannabis are typically smoked in joints, either with or without tobacco (Hindocha et al., 2016); though they may also be used in a water pipe (i.e. bong) or vaporisers (electronic devices which heat cannabis into a vapour for inhalation; Russell et al., 2018) which may influence the pharmacokinetics and transient effects of THC (Spindle et al., 2018). Evidence suggests that among these products, those with higher THC concentrations confer the greatest harms, including increased severity of dependence (Freeman and Winstock, 2015), cannabis use disorder symptom onset and treatment (Freeman et al., 2018b; Arterberry et al., 2019) and a greater risk of, and relapse to psychosis (Di Forti et al., 2015; Schoeler et al., 2016; Di Forti et al., 2019). However, few studies have explored the risk of harms carried by the more novel products becoming increasingly prevalent.
One of the most rapidly proliferating forms of cannabis, known broadly as cannabis concentrates, are extremely potent extracts produced through advanced methods of extraction. These include butane, or other solvent-based extraction (e.g. butane hash oil), or combined heat and pressure (e.g. Rosin) with products often differentiated by specific labels describing their consistency (e.g. shatter, wax, budder; Caulkins et al., 2018). As these efficient methods of extraction allow the cannabinoids to be removed from trichomes, the potencies of these products (which can reach 70–80% and potentially higher; Raber et al., 2015) can exceed those produced from sift extraction, such as Kief (a powdery substance consisting of loose trichomes that are often extracted from plant material using manual sifting). These cannabis concentrates are typically consumed via a process known colloquially as ‘dabbing’ in which the vapours created through heating (usually via electronic vaporisers or heated glass/aluminium rods) the highly refined concentrates are inhaled. This method can enable rapid consumption of high doses of THC, and users report stronger and longer lasting effects than that from smoked cannabis (Loflin and Earleywine, 2014). The increasing prevalence of concentrates is evident from both sale and seizure data from the USA (Smart et al., 2017; Chandra et al., 2019), and although an understudied area, early research suggests that their use is associated with poorer mental health (Chan et al., 2017) and increased symptoms of dependence (Loflin and Earleywine, 2014; Meier, 2017); though evidence is mixed (Bidwell et al., 2018; Sagar et al., 2018).
Also gaining prominence, particularly in legal markets (Borodovsky et al., 2016) and among medicinal users (Pacula et al., 2016) are cannabis infused foods (edibles) and liquids. Pharmacokinetically distinct from inhalation, the onset of effects are delayed but have a longer duration when cannabis is ingested (Huestis, 2007); potentially making it more difficult for users to titrate their dose and experience their desired level of intoxication. Also, while THC’s bioavailability is much lower when consumed orally, a single commercially available edible product in the USA can contain up to 100 mg of THC (10 servings; although some states impose restrictions beyond 50 mg; Gourdet et al., 2017). Offering a non-combustible alternative to cannabis consumption, and often produced and marketed in the form of sweet food products (i.e. brownies and confectionary), there is growing concern that the widespread availability of edibles may increase the likelihood of initiation and frequency of use among young people (MacCoun and Mello, 2015).
Previous studies investigating the effects of different types of cannabis use typically assign participants to separate groups according to the type of cannabis they most commonly use. However, grouping participants in this way fails to characterise the full range of cannabis products used and how these differ across individuals. As global drug markets rapidly evolve, developing a richer understanding of cannabis use patterns across a wide range of products is necessary to understand cannabis use and its consequences. One approach to studying this issue is to use person-centred analyses (such as latent class analysis; LCA) which can capture the heterogeneity in, and characterise distinct profiles of, cannabis use and then compare these groups across key health-related outcomes. Studies utilising these approaches have typically identified subgroups of people who use cannabis describing different affective, involvement (i.e. frequency and consequences of use) and/or risk profiles (Pearson et al., 2017; Manning et al., 2018). Although other studies have used these approaches to distinguish groups by various cannabis use characteristics, including products preferred/used (e.g. Korf et al., 2007; Krauss et al., 2017), defining classes/clusters using the types of cannabis individuals use in addition to other features of cannabis use not related to product use fails to entirely characterise the specific heterogeneity in the profiles of cannabis products being used. In addition, by not exploring differences in important health related outcomes across these subgroups, these studies were not able to characterise the risk of harm associated with the different profiles of cannabis use. We are unaware of any previous studies that have both parsed people who use cannabis into groups specifically on the basis of their use of different cannabis products, and then explored variations in health-related outcomes, in particular, dependence between those classes/groups. To address this gap, we used LCA to differentiate groups of people who use cannabis (recruited in the Global Drug Survey, GDS, 2018, a large multi-national survey) using six different cannabisproduct indicators (sinsemilla, herbal, hashish, concentrates (e.g. BHO, oil), kief & edibles). To validate the LCA solution, we then compared rates of mental health diagnoses and probable dependence across these latent classes.