January 12, 2026

expert reaction to paper proposing thresholds for cannabis use, as published in Addiction

A study published in Addiction looks at risk thresholds for cannabis use. 

Dr Marta Di Forti, MRC Senior Clinical Fellow, Institute of Psychiatry, Psychology, and Neuroscience (IoPPN), King’s College London, said:

“Using a standardising measure such as THC units to estimate cannabis consumption and thresholds for harmful use can indeed become an important tool both in research , and in the future in clinical settings. Alcohol units have also proven very helpful in empowering people with the concept of a “threshold” for harm to self-regulate when trying to maintain a safe and controlled consumption . 

“I think it is important to remember that cannabis unlike alcohol does not contain only one active ingredient but over 144 cannabinoids . Moreover, among those already studied other cannabinoids other than THC have shown intoxicating and harmful effects (e.g THCP) some of which also depend on the mode of consumption ( e.g. delta-8 THC,) not captured by THC units. In the US, for instance, some of these cannabinoids are present in higher concentration than THC in some of the types of cannabis most available to adolescents. What is popular in the US soon follows across the Atlantic. Nevertheless, THC units are, undoubtably a very important and much needed start.”

Prof David Nutt, The Edmond J Safra Chair and Head of the Centre for Neuropsychopharmacology, Division of Brain Sciences, Dept of Medicine, Imperial College London, and Chair of the scientific committee of DrugScience, said:

“This analysis provides a welcome update on the risks of recreational THC use leading to dependence. The data provide an estimate of a threshold of weekly consumption to eliminate dependence risk of less than 40mg/week in adults (and less than 30 for adolescents).  What needs to be done now is to facilitate recreational cannabis users in determining exactly how much they are using to help them control their risk, in the same way as we currently do with alcohol units. The best way would be through a regulated cannabis market with clear product quality and identification of Unit amounts (as required for alcohol currently) plus a credible and honest educational programme. Also it is important for users of prescribed medical cannabis to know that these products have a lower risk of dependence because of their nature  (significant cannibidiol levels), their route of administration (oils) and the way in which they are used (i.e. not to get high).”

‘Estimating thresholds for risk of cannabis use disorder using standard delta-9-tetrahydrocannabinol (THC) units’ by Rachel Lees Thorne et al. was published in Addiction at 9:00am UK time on Monday 12^th January

DOI: https://doi.org/10.1111/add.70263

Declared interests

Professor Marta di Forti: MDF reports personal fees from Janssen outside the submitted work.  Educational seminar sponsored by Recordati and a meet the expert lecture sponsored by Lumbeck/Otzuka. Topics Treatment of Dual Diagnosis, in particular Psychosis with comorbid cannabis dependence.

Prof David Nutt: DJN is chair of the scientific committee of charity DrugScience that ran the T21 medical cannabis initiative and receives unrestricted educational grants from some cannabis companies