Researchers in the UK have proposed new thresholds for monitoring cannabis use – modelled on alcohol units – which they say could help people avoid potentially harmful consumption.
The threshold recommendations, proposed in a paper published in the journal Addiction, are based on a system for measuring cannabis consumption not by weight but by THC content and tracking potency and quantity, rather than only frequency of use.
In the new paper, the researchers applied this unit to establish thresholds at which cannabis could be considered ‘safer’.
The research drew on data from the CannTeen study conducted at UCL, which tracked 150 people who used cannabis, assessed the severity of Cannabis Use Disorder (CUD), and estimated their weekly THC unit intake over a year.
Defined in the DSM-5 as a ‘problematic pattern of cannabis (marijuana) use leading to clinically significant impairment or distress’, CUD is thought to affect around 22% of consumers and 13 million people globally. Symptoms can include cravings, struggling to control use, and cannabis interfering with work, family, or other relationships.
The team established that adults should not exceed 8 THC units per week, equivalent to about 40 mg of THC or 1/3 gram of cannabis flower.
The risk of CUD was said to increase above 8 THC units per week, with the risk of more severe CUD rising above 13 units per week.
In the CannTeen sample, 80% of people who used below 8 THC units did not have CUD, while 70% who used above this amount reported CUD.
In the same way that guidelines for safer alcohol use focus on standard units, the researchers from the University of Bath propose that a similar unit could be applied to cannabis to help people monitor consumption and keep it within recommended limits.
“Cannabis is one of the most widely used drugs in the world. Despite this, there is no information for consumers about how different levels of consumption might affect them,” said Professor Tom Freeman, co-author of the study and a researcher at the Bath Department of Psychology.
“Safer use thresholds based on standard THC units could help people better understand their level of use and make informed choices about their health. Such thresholds could be used by public health bodies and in healthcare settings for communicating the risks of an individual’s level of consumption, and for tracking reductions in use.”
He added: “As cannabis becomes increasingly available in legal markets around the world, it is more important than ever to help consumers make informed choices about their use.”
International push for better product labelling
The research has attracted international interest from countries with regulated cannabis markets, such as Canada, where there is said to be growing momentum to include THC unit information on product labelling.
The research team has shared its findings with the Canadian Centre on Substance Use and Addiction (CCSA), which is leading a global working group on cannabis units.
Dr Robert Gabrys, senior research and policy analyst at the CCSA, said Canada’s expert panel for the legislative review of the Cannabis Act has made it a priority to develop a ‘standard dose’ for cannabis products.
“Cannabis legalisation in Canada has brought a much wider range of products to the market,” he commented.
“With that, many people face challenges understanding product labels and how to safely dose their cannabis products. This has led to the need for more effective approaches to help people interpret product information and better understand the potential health effects of their cannabis use.”
Balancing the harms and risks
Patients using cannabis for the treatment of a medical condition or symptom management routinely use higher doses of cannabis, more frequently, and are more likely to use it long-term.
While the study wasn’t designed to evaluate cannabis being used medicinally, it could still raise important questions for patients and clinicians when prescribing cannabis-based medicines.
According to the study co-author, Dr Rachel Lees Thorne, the research “does not speak to whether the risk of CUD is different across intention to use” and prescribing clinicians will need to “balance the harms and risks of the treatment they provide”.
“Our findings indicate that increasing THC consumption is associated with increased CUD risk. Other factors will likely influence this risk, and careful clinical management will assess the appropriate identification and monitoring of risk in this setting,” Dr Lees Thorne told Cannabis Health, when asked about the considerations for medical use.
“Previous research indicates that rates of CUD are similar in those who report cannabis use for medicinal purposes to those who report use for non-medical reasons. Therefore, monitoring of total THC intake as well as for CUD symptoms may benefit the health of those who use cannabis for both non-medical and medical purposes.”
She added: “As with all medical decision-making, clinicians will need to balance the harms and risks of the treatment they provide. Our findings are not intended for use as a THC limit for those being prescribed cannabis medicinally, and clinicians will need to weigh up the risk of CUD with symptom relief. THC units could instead be employed in a medical context as a helpful tool to monitor consumption and risk.”
A “starting point” for an evidence-based framework
Building on these initial findings, the team now plans to look at safer cannabis thresholds across larger international samples to develop tools to help people track their unit consumption in different contexts.
“There is currently a clear unmet need across research, public health, and policy for a common way of talking about cannabis dose and risk,” said Dr Lees Thorne.
“We hope that this research provides a starting point for an evidence-based framework around thresholds for health harms from THC unit consumption. These initial findings warrant replication across larger samples and other health concerns.”
