INTRODUCTION
An estimated 22% of people who use cannabis will develop cannabis use disorder (CUD), [1]. CUD refers to a pattern of cannabis use that causes clinically significant impairment or distress. Symptoms include using cannabis for longer than intended, tolerance to the effects of cannabis, not meeting obligations at work/school because of cannabis use and spending a lot of time getting, using or recovering from the effects of cannabis [2]. Cannabis use is responsible for 35% of European Union drug treatment entrants and is cited as a problem drug by 87% of those under 18 years old in drug treatment in the United Kingdom (UK) [3, 4]. Most people with CUD do not seek out professional treatment [5, 6], with non-treatment seekers citing preference for informal treatment options and desire to be self-reliant [7, 8]. Despite this, there is little quantitative guidance on how an individual who uses cannabis can reduce their likelihood of developing CUD.
Previous research has identified factors that might increase an individual’s risk of developing symptoms of CUD. One increasingly recognised factor appears to be how cannabis is used, including aspects of use behaviour such as frequency and quantity, as well as type, and relatedly the potency of cannabis product used. Frequency of use has been found to have a dose–response relationship with risk for CUD, whereby increased frequency (e.g. using daily vs. weekly vs. monthly) is associated with increased risk of CUD [9].
However, research indicates that other factors relating to use are involved in conferring risk for CUD, which are not always well quantified in research. For example, cannabis potency [% delta-9-tetrahydrocannabinol (THC)] has been increasing for several decades [10] and use of high potency cannabis is associated with an increased risk of negative outcomes, including CUD and adverse mental health [11, 12]. Furthermore, quantity of cannabis used has also been linked to increased risk of CUD [13–15], and like cannabis potency, provides important data that is not captured in studies investigating frequency of use alone.
Recent consensus from different expert collaborations has highlighted the importance of increased sensitivity of data collection around cannabis use [16]. Collecting high-quality data around cannabis use that can be harmonised across research studies can help to accurately assess outcomes related to cannabis use, including CUD. Furthermore, increasing accuracy of measurement may result in more practical harm reduction advice for cannabis users hoping to reduce their risk of CUD or other harms. For example, researchers developing lower-risk cannabis use guidelines [17], reviewed previous evidence and concluded that a reduction in frequency of days per week, using lower-potency products as well as delaying onset of cannabis use until after the duration of puberty may reduce cannabis-related harms. However, there is currently a lack of evidence to propose specific guidance around quantity of cannabis use to reduce cannabis-related harms. Dose-related information (based on standard alcohol units or standard drinks) is the cornerstone of alcohol harm reduction guidance in many countries around the world. For example, in the United Kingdom, people who drink alcohol are advised not to regularly consume more than 14 units of alcohol per week to reduce the risk of harm. There are currently no such quantitative guidelines for safer levels of cannabis use. This presents a key unmet public health need, given increases in cannabis use, cannabis potency and treatment need internationally [18].
Previous proposals to improve data collection of cannabis quantity and estimate risk thresholds include the ‘standard joint unit’ of 7 mg of THC, a quantity chosen based on median quantities present in joints donated to researchers by people who use cannabis [19]. The standard joint unit represents an improvement from relying on frequency-only measures, by directly considering quantity of THC consumed. Researchers have previously proposed 1 standard joint unit per day as a threshold for moderate risk of having cannabis-related problems [using the cannabis abuse screening test (CAST)] in individuals with heavy cannabis use [14]. However, the dose of THC used in a joint may vary between and within individuals (e.g. morning vs. evening use). Additionally, many people use several methods of administration as well as different types of cannabis that vary in THC quantity, that would not be captured by only measuring the number of joints used. However, research using the standard joint unit provides proof-of-concept evidence for the use of a quantity-based measure (number of joints consumed) to discriminate risk of problematic cannabis use.
Other recent proposals include measuring cannabis use by the quantity of THC consumed across all cannabis products and administration methods. This is particularly relevant given the increasing diversity of different cannabis types including high potency concentrates that have been observed in newly legal markets [20, 21]. Research has indicated that in daily users of cannabis, increasing the quantity of THC consumed per day is associated with an increased number of CUD symptoms [22]. A standard ‘unit’ of 5 mg THC has been proposed [23], and implemented by the United States (US) National Institutes of Health, who now mandate the use/reporting of THC units in research they fund [24]. Using baseline data from the CannTeen study (a 12-month observational longitudinal dataset of adult and adolescent cannabis users) we recently validated a method of estimating standard THC units in observational studies, using an Enhanced Cannabis Timeline Followback (EC-TLFB) [22]. Standard THC units provided the strongest correlation with urinary markers of cannabis use (creatinine-adjusted THC-COOH) of all cannabis use measures included. Following this validation, we now present evidence on the ability of standard THC units (estimated using the EC-TLFB, which was administered every 3 months for 1 year in the longitudinal CannTeen study) to discriminate risk of Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) CUD. This article represents what we believe is the first attempt to determine thresholds for risk of CUD by weekly standard THC units consumed.
The current study aimed to establish preliminary risk thresholds for CUD from standard THC units using receiver operating characteristic (ROC) curve analysis. We aimed to identify thresholds for any CUD (mild, moderate or severe), as well as greater severity, at least moderate CUD. The CannTeen study includes matched groups of adolescents (age, 16–17 years old) and adults (age, 26–29 years old). This is important because prevalence of cannabis use is particularly high in adolescent groups, who also are more vulnerable to development of CUD than adults or older age groups [1, 25–27]. Although the only way of ensuring no harm from cannabis is to not use at all [17], people who use cannabis could benefit from accurate information regarding their risk, particularly in high-risk groups (e.g. adolescents). Therefore, in the current study we used data from both adolescents [16, 17] and adults [25–28] to estimate the ability of standard THC units to discriminate risk of CUD separately by age group. We hypothesised that all ROC curves would have an area under the curve (AUC) greater than or equal to 0.70, indicating a good discrimination (and significantly better than chance) of THC units on the classification of individuals as CUD/no CUD.
METHOD
Cannabis research context
This study used data from CannTeen, a longitudinal study of adult and adolescents who use cannabis in London, United Kingdom, that ran from November 2017 to June 2021 (sessions after 23 March 2020 adapted to virtual data collection during the national coronavirus disease 2019 lockdown periods in the United Kingdom). To put our research into a wider context [28], recreational cannabis use in the United Kingdom is illegal, and possession and supply can result in legal penalties. Medicinal cannabis was legalised in 2018, however, access remains very limited, and it can only be prescribed by specialist doctors in limited circumstances. Cannabis is the most used illicit drug in the United Kingdom, with an estimated 6.8% of the adult population, and 13.8% of the young adult population reporting use in the past year [29]. Most people who use cannabis in the United Kingdom do so by mixing herbal cannabis (estimated at 14.2% potency) [30] with tobacco into ‘joints’ [31], although administration methods and products do vary, as was evidenced in the current study.
Read more
https://onlinelibrary.wiley.com/doi/10.1111/add.70263
https://cannabishealthnews.co.uk/2026/01/23/researchers-propose-thc-units-for-safer-cannabis-use/
