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

Tom P Freeman, Peggy van der Pol, Wil Kuijpers, Jeroen Wisselink, Ravi K Das, Sander Rigter, Margriet van Laar, Paul Griffiths, Wendy Swift, Raymond Niesink, Michael T Lynskey

Research output: Contribution to journalArticle

40 Citations (Scopus)
52 Downloads (Pure)

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.

Original languageEnglish
Pages (from-to)2346-2352
Number of pages7
JournalPsychological Medicine
Volume48
Issue number14
Early online date31 Jan 2018
DOIs
Publication statusPublished - 31 Oct 2018

Keywords

  • addiction
  • cannabis
  • drug treatment
  • mental health
  • potency
  • psychosis
  • δ-9-tetrahydrocannabinol

ASJC Scopus subject areas

  • Applied Psychology
  • Psychiatry and Mental health

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