For the first time, researchers have proposed thresholds at which cannabis use could be considered “safer.”
“The only truly safe level of cannabis use is no use,” said study author Rachel Lees Thorne, research associate in the department of psychology at the University of Bath (UK). “However, for those who don’t want to stop or are unable to, we still want to make it easier for them to lower their risk of harm.”
The new threshold recommendations are based on a system for measuring cannabis consumption not by weight but by THC content. In the same way guidelines for safer alcohol use focus on number of drinks by ounces, Thorne and her colleagues propose something similar for cannabis.
Published in the journal Addiction, the findings recommend that adults should not exceed 8 THC units per week—equivalent to about 40 mg of THC or 1/3 gram of herbal cannabis. Above these thresholds, people are at greater risk of developing cannabis use disorder, a condition that affects an estimated 22% of people who regularly use cannabis. CUD—similar to alcoholism—is a problematic pattern of cannabis use causing clinically significant impairment or distress. Symptoms can include cravings, struggling to control use, and cannabis interfering with work, family and other relationships.
For the study, the researchers drew on data from the CannTeen study conducted at University College London, which tracked 150 people who used cannabis, estimated their weekly THC unit intake over a year, and assessed the severity of cannabis use disorder.
The team established that for adults, the risk of CUD increases above 8 THC units per week, with the risk of more severe CUD rising above 13 units per week. For example, 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.
“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. Safer use thresholds based on standard THC units could help people better understand their level of use and make informed choices about their health,” said study co-author Tom Freeman, Director of the Addiction and Mental Health Group at the University of Bath. “Such thresholds could also 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.”
After focusing this study on cannabis use in the UK, Thorne, Freeman and team said they plan to take an international perspective next. They are now looking at safer cannabis thresholds across larger international samples and developing tools to help people track their unit consumption in different international contexts.
The UK-based research has already attracted attention from stakeholders in Canada, where there’s a movement to include THC information on cannabis product labeling. In fact, 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 legalization in Canada has brought a much wider range of products to the market. 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,” said Robert Gabrys, senior research and policy analyst at the Canadian Centre on Substance Use and Addiction. “[The Bath research] is an important part of this effort, as it demonstrates how a standard THC unit can be used to predict and communicate health risks, in this case CUD.”