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

Psychol Med. 2018 Jan 31:1-7. doi: 10.1017/S0033291717003877. [Epub ahead of print] Freeman TP1, van der Pol P2, Kuijpers W3, Wisselink J3, Das RK4, Rigter S2, van Laar M2, Griffiths P5, Swift W6, Niesink R2, Lynskey MT1. Author information 1 National Addiction Centre, Institute of Psychiatry, Psychology and Neuroscience, King's College London,London,UK. 2 Trimbos Institute, Netherlands Institute of Mental Health and Addiction,Utrecht,the Netherlands. 3 Stichting Informatievoorziening Zorg, National Alcohol and Drugs Information System,Houten,the Netherlands. 4 Clinical Psychopharmacology Unit,University College London,London,UK. 5 European Monitoring Centre for Drugs and Drug Addiction,Portugal. 6 National Drug and Alcohol Research Centre, UNSW Australia,Sydney,NSW,Australia. 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: δ-9-tetrahydrocannabinol; addiction; cannabis; drug treatment; mental health; potency; psychosis PMID: 29382407 DOI: 10.1017/S0033291717003877