Comparison of brief versus extended personalised feedback in an online intervention for cannabis users: short-term findings of a randomised trial

Jan Copeland, Sally Rooke, Dan Rodriquez, Melissa M. Norberg, Lisa Gibson*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)


Previous studies have shown brief online self-help interventions to be a useful method of treating cannabis use and related problems; however, no studies have compared the effects of brief versus extended feedback for online brief intervention programs. Objectives: The current study was a two arm randomised trial aimed at testing the short term effectiveness of a brief and extended feedback version of Grassessment, a brief online intervention for cannabis users that provides individualised feedback regarding use, motives, and harms. Methods: Participants (n = 287) reporting at least one symptom of DSM IV cannabis abuse or dependence were recruited using online and offline advertising methods. Participants were randomised to receive either a brief or extended feedback version of the Grassessment program and were required to complete a one month follow up questionnaire. Results: One hundred and ninety four participants completed the one month follow up. Wilcoxon analyses showed a significant decrease in past month quantity and frequency of cannabis use (ps <. 0.001; r = -0.41 and -0.40 respectively) and lower severity of dependence scores (p = 0.002; r = -0.31) among those in the brief feedback condition. Participants in the extended feedback group also demonstrated significant decreases in patterns of use (ps <. 0.002; r = -0.39 and -0.33) but not severity of dependence (p = 0.09; r = 0.18). A Generalized Estimating Equation (GEE) analysis showed no significant interaction between length of feedback received and past month cannabis use frequency (p = 0.78), quantity (p = 0.73), or severity of dependence (p = 0.47). Conclusion: This study adds support for the use of brief online self-complete interventions to reduce cannabis use and related problems in the short term. The findings suggest that in the case of the brief online screening and feedback program Grassessment, extended feedback does not lead to superior outcomes over brief feedback.

Original languageEnglish
Pages (from-to)43-48
Number of pages6
JournalJournal of Substance Abuse Treatment
Publication statusPublished - May 2017


  • cannabis
  • marijuana
  • brief intervention
  • self-help
  • online
  • web based


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