University of Bath psychologists have proposed the first evidence-based THC unit thresholds to guide safer cannabis use, echoing alcohol unit guidelines. Their goal is to give people clearer information to monitor their intake and lower the risk of cannabis use disorder.
How much cannabis is too much? A team of psychologists in the UK is trying to give people a clearer answer, borrowing a page from the playbook used to guide safer alcohol use.
Researchers at the University of Bath have proposed the first evidence-based thresholds for what they describe as safer cannabis consumption, based not on the weight of the drug but on how much THC it contains. THC, or delta-9-tetrahydrocannabinol, is the main compound responsible for cannabis’s psychoactive effects.
The work, published in the journal Addiction, suggests that adults who choose to use cannabis should aim not to exceed 8 THC units per week. That is roughly equivalent to 40 milligrams of THC, or about one-third of a gram of typical herbal cannabis.
The idea is similar to alcohol guidelines in the UK, where adults are advised not to regularly exceed 14 alcohol units per week. Instead of counting drinks, people would count THC units, which reflect both how strong a product is and how much of it someone uses.
The researchers argue that focusing on THC units could help people, clinicians and public health agencies move beyond simple measures like how many days per week someone uses cannabis.
They also emphasize that no level of cannabis use is risk-free.
“The ultimate goal of our new guidelines is to reduce harm. The only truly safe level of cannabis use is no use. 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. For instance, a person might opt to use lower-THC products or reduce the quantity of cannabis they use,” lead author Rachel Lees Thorne, a research associate in Bath’s Department of Psychology, said in a news release.
Cannabis is one of the most widely used drugs worldwide, and as products have become more potent, concerns have grown about cannabis use disorder, or CUD. CUD is a pattern of use that leads to significant distress or problems in daily life, such as intense cravings, difficulty cutting down, or cannabis use interfering with work, school or relationships. In a prior study, researchers estimated that about 22% of people who regularly use cannabis develop CUD.
To link THC intake with that risk, the Bath team drew on data from the CannTeen study, led at University College London. That observational study followed 150 people who used cannabis over the course of a year. Researchers estimated each person’s weekly THC unit intake and assessed how severe their cannabis use disorder symptoms were.
From those data, the Bath researchers identified thresholds where risk appears to rise. For adults, they found that the likelihood of having CUD increases above 8 THC units per week, and the risk of more severe CUD climbs above 13 units per week. In the CannTeen sample, most people who stayed under 8 units did not meet criteria for CUD, while most people who used more than that did.
The team’s proposal is not meant to encourage cannabis use, but to give people who already use it a practical way to monitor and potentially reduce their intake. In public health, this is known as a harm reduction approach: accepting that some people will use a substance, and focusing on strategies that can lower the chances of serious problems.
The researchers also see potential for THC units to become a common language in health care and policy.
“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,” added senior author Tom Freeman, a professor in Bath’s Department of Psychology.
Right now, many cannabis products are labeled by weight or by percentage of THC, which can be confusing for consumers trying to compare items or figure out how much they are actually taking in. A standard THC unit system could simplify that, especially in legal markets where a wide range of edibles, oils, vapes and high-potency flowers are available.
The Bath team’s findings are already drawing interest abroad, particularly in Canada, where recreational cannabis has been legal since 2018. Canadian regulators and researchers have been exploring the idea of a standard cannabis dose that could be used on product labels, similar to how alcohol units appear on beer, wine and spirits in the UK.
The Canadian Centre on Substance Use and Addiction (CCSA) is leading a global working group on cannabis units, and the Bath researchers have shared their results to support that effort. CCSA senior research and policy analyst Robert Gabrys has highlighted the challenges many Canadians face in interpreting cannabis product labels and dosing their use safely, especially as the market has expanded.
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,” Gabrys said in the news release.
Next, the Bath team plans to test and refine their proposed thresholds in larger, international samples. They also hope to develop practical tools that can help people calculate and track their THC units across different products and legal systems.
If those tools and thresholds are adopted, future cannabis users might one day be able to check their weekly THC units as easily as many drinkers now tally alcohol units. For people who choose to use cannabis, the researchers say, that kind of clear information could make the difference between casual use and a pattern that starts to take over their lives.
Source: University of Bath