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Changes in cannabis potency and first-time admissions to drug treatment: a 16-year study in the Netherlands

Published online by Cambridge University Press:  31 January 2018

Tom P. Freeman ,
Peggy van der Pol ,
Wil Kuijpers ,
Jeroen Wisselink ,
Ravi K. Das ,
Sander Rigter ,
Margriet van Laar ,
Paul Griffiths ,
Wendy Swift  and
Raymond Niesink
...Show all authors
Tom P. Freeman*
Affiliation:
National Addiction Centre, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK Clinical Psychopharmacology Unit, University College London, London, UK
Peggy van der Pol
Affiliation:
Trimbos Institute, Netherlands Institute of Mental Health and Addiction, Utrecht, the Netherlands
Wil Kuijpers
Affiliation:
Stichting Informatievoorziening Zorg, National Alcohol and Drugs Information System, Houten, the Netherlands
Jeroen Wisselink
Affiliation:
Stichting Informatievoorziening Zorg, National Alcohol and Drugs Information System, Houten, the Netherlands
Ravi K. Das
Affiliation:
Clinical Psychopharmacology Unit, University College London, London, UK
Sander Rigter
Affiliation:
Trimbos Institute, Netherlands Institute of Mental Health and Addiction, Utrecht, the Netherlands
Margriet van Laar
Affiliation:
Trimbos Institute, Netherlands Institute of Mental Health and Addiction, Utrecht, the Netherlands
Paul Griffiths
Affiliation:
European Monitoring Centre for Drugs and Drug Addiction, Portugal
Wendy Swift
Affiliation:
National Drug and Alcohol Research Centre, UNSW Australia, Sydney, NSW, Australia
Raymond Niesink
Affiliation:
Trimbos Institute, Netherlands Institute of Mental Health and Addiction, Utrecht, the Netherlands
Michael T. Lynskey
Affiliation:
National Addiction Centre, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK
*
Author for correspondence: Tom P. Freeman, E-mail: tom.freman@kcl.ac.uk
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Abstract

Background

The number of people entering specialist drug treatment for cannabis problems has increased considerably in recent years. The reasons for this are unclear, but rising cannabis potency could be a contributing factor.

Methods

Cannabis potency data were obtained from an ongoing monitoring programme in the Netherlands. We analysed concentrations of δ-9-tetrahydrocannabinol (THC) from the most popular variety of domestic herbal cannabis sold in each retail outlet (2000–2015). Mixed effects linear regression models examined time-dependent associations between THC and first-time cannabis admissions to specialist drug treatment. Candidate time lags were 0–10 years, based on normative European drug treatment data.

Results

THC increased from a mean (95% CI) of 8.62 (7.97–9.27) to 20.38 (19.09–21.67) from 2000 to 2004 and then decreased to 15.31 (14.24–16.38) in 2015. First-time cannabis admissions (per 100 000 inhabitants) rose from 7.08 to 26.36 from 2000 to 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, b = 0.370 (0.317–0.424), p < 0.0001. After adjusting for age, sex and non-cannabis drug treatment admissions, these positive associations were attenuated but remained statistically significant at lags of 5–7 years and were again strongest at 5 years, b = 0.082 (0.052–0.111), p < 0.0001.

Conclusions

In this 16-year observational study, we found positive time-dependent associations between changes in cannabis potency and first-time cannabis admissions to drug treatment. These associations are biologically plausible, but their strength after adjustment suggests that other factors are also important.

Keywords

addictionmental healthpsychosisdrug treatmentcannabisδ-9-tetrahydrocannabinolpotency
Type
Original Articles
Information
Psychological Medicine , Volume 48 , Issue 14 , October 2018 , pp. 2346 - 2352
Copyright
Copyright © Cambridge University Press 2018 

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