A new study from the University of Bath, led by Rachel L. Thorne and published in Addiction, offers the first concrete weekly THC dose thresholds linked with a higher risk of cannabis use disorder (CUD). Rather than relying on vague terms such as “a lot,” the team used a standardized THC unit to estimate when typical use becomes risky.
What the study measured
Researchers analyzed data from the CannTeen study, following 150 people who had used cannabis in the prior year: 85 adolescents aged 16–17 and 65 adults aged 26–29. They created a THC unit equal to 5 milligrams of THC, modeled on the standard drink unit used in alcohol research. Participants reported cannabis use repeatedly over one year and received a clinical assessment at the end to determine whether they met criteria for cannabis use disorder.
Thresholds identified
– Adolescents: elevated CUD risk began at about 6 THC units per week, roughly 30 mg of THC.
– Adults: elevated CUD risk began at about 8 THC units per week, roughly 40 mg of THC.
Thresholds for moderate to severe CUD were higher. The authors stress that only complete abstinence removes the risk entirely; these thresholds identify points where risk climbs noticeably.
Why a THC unit matters
Standardized units help translate consumption into comparable measures for research, public messaging, screening and prevention. THC is the primary ingredient linked to dependence risk, but cannabis products are chemically complex. Other cannabinoids, product potency, and the route of administration (smoking, vaping, edibles) all change effects and risk. Jakob Manthey of the University of Hamburg notes unit thresholds can be useful for communication but warns they should not be read as implying lower consumption is risk-free.
Strengths and limitations
A strength of the study is repeated measures from the same participants across a year, which improves reliability compared with one-off surveys. Important limitations include the small sample size (150 people) and reliance on estimated THC content from external sources rather than lab analysis of the exact products participants used. Because of these limits, the thresholds should be treated as preliminary guidelines rather than absolute limits. Nonetheless, the data show a clear pattern: higher weekly THC intake is associated with greater CUD risk.
Clinical and public health uses
These thresholds are not a diagnostic substitute but could be a practical screening tool. Clinicians and school or community health workers might ask patients how many THC units they consume weekly to flag elevated risk and prompt further assessment. Standardized units could also make research and surveillance data more comparable across studies and jurisdictions.
What units cannot solve alone
In many places consumers lack reliable information about product THC content, especially for home-grown or illicit supplies. Without clear labeling and regulation, people cannot accurately convert their consumption into THC units. British neuropsychopharmacologist David Nutt called the study an important step and argued for regulated markets with consistent product quality and clear unit labeling, similar to alcohol policy.
Bottom line
The study provides initial, concrete weekly THC thresholds that mark where cannabis use disorder risk increases—about 30 mg THC per week for adolescents and about 40 mg per week for young adults. These figures are useful as communication and screening aids but are not definitive limits. Reducing harm will require better product information and broader prevention and policy measures in addition to any unit-based guidance.