Are changes in cannabis potency associated with new admissions to drug treatment?

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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). 



Background: The number of people entering specialist drug treatment for cannabis problems has risen considerably in recent years, especially in Europe. The reasons for this are unclear, but rising cannabis potency could be a contributing factor. Here we sought to test this hypothesis using sixteen years of monitoring data in the Netherlands.

Methods: Cannabis samples were purchased from a random sample of retail outlets each year from 2000 to 2015 and analysed for their potency (delta-9-tetrahydrocannabinol, THC). Mixed effects linear regression models were used to test associations between THC and first-time admissions to cannabis treatment, retrieved from a national database. Candidate time lags (0-10 years) were based on normative European data for treatment of cannabis problems.

Outcomes: THC concentrations increased from a mean (95% CI) of 8.62 (7.97, 9.27) in 2000 to 20.38 (19.09, 21.67) in 2004 and then decreased to 15.31 (14.24, 16.38) in 2015. First-time cannabis admissions rose from 7.08 to 26.36 per 100,000 inhabitants between 2000 and 2010, and then decreased to 19.82 in 2015. THC was positively associated with treatment entry at lags of 0-9 years, with the strongest association at 5 years.

Interpretation: In this sixteen-year study, changes in cannabis potency were positively associated with subsequent cannabis admissions to drug treatment services. These findings do not establish causality but are biologically plausible, and potentially relevant in the context of increases in cannabis potency, treatment for cannabis problems, and global policy reform.

November 2017


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