The safety and scientific validity of this study is the responsibility of the study sponsor and investigators. Listing a study does not mean it has been endorsed by the ANZCTR. Before participating in a study, talk to your health care provider and refer to this information for consumers
Trial registered on ANZCTR

Registration number
Ethics application status
Date submitted
Date registered
Date last updated
Type of registration
Prospectively registered

Titles & IDs
Public title
Feasibility Study of a Brief Telephone-based Cannabis Intervention
Scientific title
A brief telephone-based intervention for treatment seeking cannabis users with the primary outcome of cannabis use frequency
Secondary ID [1] 287739 0
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Cannabis Use Disorder 296602 0
Condition category
Condition code
Mental Health 296866 296866 0 0

Study type
Description of intervention(s) / exposure
Brief (60 minute) one session telephone-based intervention based on motivational interviewing and cognitive behavioural therapies. This call will be made by the counsellors working at the Cannabis Information Helpline who will receive intervention training. In addition to this training, adherence will be monitoring by the Helpline supervisors as well as by research staff who will listen to approximately 20% of the sessions.
Intervention code [1] 293136 0
Intervention code [2] 293149 0
Comparator / control treatment
Do-It-Yourself workbooklet on reducing cannabis use
Control group

Primary outcome [1] 296454 0
Frequency of cannabis use assessed by telephone interview with research staff
Timepoint [1] 296454 0
Three month follow-up
Secondary outcome [1] 318484 0
Cannabis-related problems assessed by telephone interview with research staff
Timepoint [1] 318484 0
Three month follow-up
Secondary outcome [2] 318485 0
Severity of cannabis dependence assessed by telephone interview with research staff
Timepoint [2] 318485 0
Three month follow-up

Key inclusion criteria
18+ Years of age
Recent cannabis use
Minimum age
18 Years
Maximum age
No limit
Both males and females
Can healthy volunteers participate?
Key exclusion criteria
Unable to give informed consent (no mental health concerns)
Dependence on other illicit substances
Recent cannabis use treatment

Study design
Purpose of the study
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
The researcher who determined if a subject was eligible for inclusion in the trial was unaware, when this decision was made, to which group the subject would be allocated. Allocation assignment will be determined after screening for inclusion criteria and gaining consent through central randomisation by computer software which will present the outcome one at a time when activated.
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
Simple randomisation using a randomisation table created by computer
Masking / blinding
Open (masking not used)
Who is / are masked / blinded?

Intervention assignment
Other design features
Not Applicable
Type of endpoint(s)
Statistical methods / analysis
The quantitative and qualitative data in this study will be analyzed using IBM SPSS Statistics, Release Version 22.
To address the study aim of determining whether intervention participants show a greater reduction in treatment outcome measures compared to the control group, an independent structure, linear model, Generalised Estimating Equation (GEE) approach to repeated measures analysis will be used to test between-group differences. GEE is appropriate for measuring the relationship between outcome variables and corresponding predictor variables over time. Prior to longitudinal modelling, two-tailed bivariate zero-order correlation analyses will be conducted between the treatment outcome variables and an indicator for the presence of any external cannabis treatment or pharmaceutical medication (dichotomous items that will be recorded at baseline and follow-up assessments). In the case of a statistically significant association, these indicator variables will be included into analyses as covariates. Similarly, to determine which baseline participant characteristics were associated with variance in cannabis-related treatment outcomes, a second series of two-tailed bivariate zero-order correlation analyses will be conducted. Due to an expected large number of comparisons for these analyses, Bonferroni corrections will be made to control for the probability of false positive findings. Finally, participant drop out in follow-up assessments will be tested prior to analysis to determine that the relevant data was missing completely at random (MCAR) using Little’s MCAR test.

As this is a pilot feasibility trial, a power analysis was not performed to determine sample size. Instead, the expected number of participants (n=100) was determined (based on the call rate to the Helpline and the project timeline) to allow for an assumed uptake of approximately 15%.

Recruitment status
Stopped early
Data analysis
Data analysis is complete
Reason for early stopping/withdrawal
Participant recruitment difficulties
Date of first participant enrolment
Date of last participant enrolment
Date of last data collection
Sample size
Accrual to date
Recruitment in Australia
Recruitment state(s)

Funding & Sponsors
Funding source category [1] 292283 0
Government body
Name [1] 292283 0
Government Department of Health
Address [1] 292283 0
Department of Health
GPO Box 9848,
Canberra ACT 2601, Australia
Country [1] 292283 0
Primary sponsor type
Peter Gates
UNSW Randwick Campus NDARC
Building R1 Level 1, 22-32 King St
Randwick NSW 2031, Australia
Secondary sponsor category [1] 290967 0
Name [1] 290967 0
Address [1] 290967 0
Country [1] 290967 0

Ethics approval
Ethics application status
Ethics committee name [1] 293756 0
University of NSW HREC
Ethics committee address [1] 293756 0
UNSW, Kensington Campus, NSW, 2052
Ethics committee country [1] 293756 0
Date submitted for ethics approval [1] 293756 0
Approval date [1] 293756 0
Ethics approval number [1] 293756 0

Brief summary
Cannabis use disorder is the most common illegal substance use disorder in the general population and demand for assistance from health professionals is increasing internationally (EMCDDA, 2014). Despite this, only a minority of individuals with the disorder seek treatment. Study on the barriers to cannabis treatment has highlighted the importance of providing additional outpatient treatments that are specific to cannabis (Treloar et al., 2007) and delivered to the individual in a way which unwanted contact with other illicit drug users can be avoided (Gates, Copeland, Swift and Martin, 2012).

To date no Australian data exists on the efficacy of such a telephone-based intervention with a specific focus on an illicit drug. This study has been funded by the Australian Government Department of Health to examine whether a brief telephone-based counselling service can act as a feasible treatment option for people with problems with their cannabis use. The results from the randomised trial may validate decisions to support the funding of telephone based services or introduce similar services for other illicit drugs.
Trial website
Trial related presentations / publications
Public notes

Principal investigator
Name 61190 0
Dr Peter Gates
Address 61190 0
UNSW Randwick Campus NDARC
Building R1 Level 1, 22-32 King St
Randwick NSW 2031Australia
Country 61190 0
Phone 61190 0
Fax 61190 0
Email 61190 0
Contact person for public queries
Name 61191 0
Dr Peter Gates
Address 61191 0
UNSW Randwick Campus NDARC
Building R1 Level 1, 22-32 King St
Randwick NSW 2031Australia
Country 61191 0
Phone 61191 0
Fax 61191 0
Email 61191 0
Contact person for scientific queries
Name 61192 0
Dr Peter Gates
Address 61192 0
UNSW Randwick Campus NDARC
Building R1 Level 1, 22-32 King St
Randwick NSW 2031Australia
Country 61192 0
Phone 61192 0
Fax 61192 0
Email 61192 0

No information has been provided regarding IPD availability
Summary results
Have study results been published in a peer-reviewed journal?
Other publications
Have study results been made publicly available in another format?
Results – basic reporting
Results – plain English summary