Can THC (Tetrahydrocannabinol) and CBD (Cannabidiol) inform standard cannabis units?

First published: 13 March 2019 | Last updated: 28 March 2019


Dr Tom Freeman

Research Associate

Tom Freeman completed his PhD at the Clinical Psychopharmacology Unit, UCL in which he investigated the cognitive mechanisms underpinning substance use and its comorbidity with psychotic disorders. His postdoctoral work involved coordinating a randomised clinical trial for cannabis addiction, funded by the Medical Research Council. This trial aims to address the growing demand for treatment of cannabis-related problems and builds on previous work at UCL on the effects of different constituents of cannabis (THC and CBD). Tom’s postdoctoral training also included designing, completing and publically disseminating a neuroimaging study investigating the effects of THC and CBD on the human brain.  Tom was recently awarded a Senior SSA Fellowship to investigate the relationship between cannabis potency and addiction at the National Addiction Centre, KCL. This programme of research will involve collaboration between researchers and agencies in the UK, Netherlands, Spain, Portugal, Australia and USA. It will employ a mixed methods approach including longitudinal monitoring programmes, global survey data and controlled experimental research.


Tom is an active member of the British Association for Psychopharmacology who have awarded him for his scientific research and public engagement. He has also received awards from the International College of Neuropsychopharmacology, the European College of Neuropsychopharmacology and the European Monitoring Centre for Drugs and Drug Addiction. Through collaborations developed at the Lisbon Addictions conference in 2015, Tom received funding to contribute to two large-scale European projects. These are currently investigating drug use in the dance music scene and biological indicators of drug use pathways in an existing cohort of young people. He has also recently received funding to investigate the effects of THC on the human brain (British Medical Association), adolescent cannabis use (Medical Research Council) and the role of CBD in cannabis-related harms (Medical Research Council).

Cannabis is used by an estimated 192 million people each year in a variety of drug markets, ranging from heavily sanctioned prohibition to commercialised legal sale. This number may rise further as new legal markets continue to emerge worldwide. The extent of harm experienced from cannabis is associated with the frequency and quantity of use. Moreover, the harmful effects of delta-9-tetrahydrocannabinol (THC) may be offset by the presence of cannabidiol (CBD) in cannabis. However, current methods for measuring cannabis use are of poor quality, providing limited information on the dose of active drug users are exposed to. Additionally, there are currently no guidelines available to encourage safer use. One possible solution to this is the concept of “standard cannabis units”. Previous proposals for these have been based on the number of grams or standard joints consumed. Alternatively, standard cannabis units could be based on fixed doses (in mg) of THC (a “standard THC unit”) and CBD (a “standard CBD unit”). This proposal has the potential to be applicable to all cannabis products (which differ markedly in THC and CBD concentrations) and all routes of administration (including vaporizers, bongs, dabbing and blunts). It can also account for the potential role of CBD in harm reduction. Developing the concept of “standard cannabis units” could improve our ability to quantify cannabis use, update our current understanding of its risks, and generate evidence-based guidelines for safer use.




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Dr Tom Freeman