Condition category
Mental and Behavioural Disorders
Date applied
Date assigned
Last edited
Retrospectively registered
Overall trial status
Recruitment status
No longer recruiting
Publication status

Plain English Summary

Background and study aims
The relationship between tobacco and cannabis use is multi-layered and can cause problems especially when co-smokers try to stop the use of one substance. However, many co-smokers are not aware of this relationship and current cessation programs usually focus on one substance. Therefore we developed the first integrative group cessation program for co-smokers of cigarettes and cannabis. This web-based study aims at enhancing co-smokers’ awareness of the relationship between tobacco and cannabis and at motivating them to quit tobacco and cannabis simultaneously.

Who can participate?
Every co-smoker of tobacco and cannabis can participate, if he/she has smoked tobacco at least once during the last 4 weeks and has used cannabis at least once during the past 6 months. There is no age restriction.

What does the study involve?
Every participant will be randomly allocated to one of three interventions:
The first intervention provides information on the relationship between tobacco and cannabis use. Participants can only read this information page by page.
The second intervention consists of two parts. In the first part, participants fill in a questionnaire on their tobacco and cannabis smoking behaviours. In the second part, they get a computer-generated feedback about their smoking behaviours. This includes comparisons of the participants’ behaviour with that of other smokers of the same age and recommendations concerning the smoking behaviour and how it could or should be changed.
In the third intervention, participants also receive questions to answer, but these are more open-ended compared to the questions of the questionnaire in the second intervention. They promote the participants reflection on their smoking behaviour, such as their personal pros and cons of quitting tobacco and/or cannabis use. Participants also get feedbacks and periodic summaries of their inputs.

What are the possible benefits and risks of participating?
The participants obtain a better understanding of their own smoking behaviours and their cessation motivation. There are no known side effects.

Where is the study run from?
The study is lead by the Swiss Research Institute for Public Health and Addiction, an associated institute to Zurich University and a World Health Organization (WHO) collaborating centre for substance abuse.

When is study starting and how long is it expected to run for?
The study started in January 2012 and will end in April 2013. Participants will be recruited within this time period.

Who is funding the study?
The study is funded by the Swiss Tobacco Prevention Fund.

Who is the main contact?
Ms. Julia Becker, Scientific Employee

Trial website

Contact information



Primary contact

Dr Michael Schaub


Contact details

Swiss Research Institute for Public Health and Addiction ISGF
Konradstrasse 32
P. O. Box
+41 44 448 11 60

Additional identifiers

EudraCT number number

Protocol/serial number


Study information

Scientific title

Brief web-based interventions to enhance co-smokers' knowledge and awareness of tobacco and cannabis co-use and to motivate them for simultaneous cessation: a randomized controlled trial


Study hypothesis

It is hypothesized that interactive web-based interventions are more effective in enhancing the motivation to quit tobacco and cannabis use simultaneously compared to mere psycho-education (= control condition).
This is a sub-study of the Integrative Cessation Program for co-smokers of cigarettes and cannabis (

Ethics approval

Ethics Committee of the Canton of Zurich, Switzerland, June 27, 2011, approval number: KEK-StV-Nr. 23/11; amendment for the internet intervention, November 11, 2011

Study design

Randomized controlled web-based study

Primary study design


Secondary study design

Randomised controlled trial

Trial setting


Trial type

Quality of life

Patient information sheet

Not available in web format, please use the contact details below to request the patient information sheet


Nicotine and cannabis use/misuse/abuse


Participants are randomly assigned to one out of the three following web-based, brief interventions:

1. Psycho-education (=control condition): mere knowledge transfer, provision of information on tobacco use, cannabis use, co-use of tobacco and cannabis, and changing smoking behaviour; the information is thematically subdivided into smaller chapters; in order to read the next chapter participants have to click a “next” button

2. Self-assessment with personalized, normative feedback: participants have to fill out two questionnaires on their tobacco and cannabis use behaviours; afterwards they receive feedbacks which are generated by an algorithm using the information given during the self-assessment; the feedbacks contain information about the frequency of use and scores (tobacco: dependence; cannabis: problematic use), including an explanation of the meaning of the scores (in relation to diagnostic cut-offs) as well as normative comparisons with reference populations of the same gender (only for tobacco) and use pattern on the basis of epidemiological data from community samples; finally, participants obtain a targeted advice to change their behaviour

3. Intervention based on principles of motivational interviewing: participants are asked mainly open-ended questions (e.g., pros and cons of quitting tobacco and cannabis); the goal is to promote the participants’ self-reflective thinking about their smoking behaviour and intentions to change it, to strengthen the abstinent-related self-efficacy, and to make participants think about the inconsistence of continued co-smoking with their personal goals; participants receive periodically affirmative feedbacks and summaries of their input

Duration of the interventions: one session not longer than 20 minutes

Intervention type



Not Applicable

Drug names

Primary outcome measure

Motivation to quit tobacco and cannabis simultaneously after intervention (t1) measured at t0, t1, t2 with a readiness ruler ranging from 1 to 10

Secondary outcome measures

1. Motivation to quit tobacco (measured at t0, t1, t2 with a readiness ruler ranging from 1 to 10)
2. Motivation to quit cannabis (measured at t0, t1, t2 with a readiness ruler ranging from 1 to 10)
3. HAPA stages of change (measured at t0, t1, t2)
4. Tobacco mean amount of cigarettes per day during last 4 weeks (measured at t0 & t2)
5. Cannabis use frequency: mean use frequency (consumption units) per day (calculated from a 7 days timeline follow-back question) and consumption frequency during last 4 weeks (8 categories) measured at t0 & t2
6. Self efficacy (to abstain from tobacco and cannabis) measured at t0, t1, t2
7. General health status (single-item-measure from SF-36) measured at t0 & t2
8. Information seeking about integrative cessation course (t2; after the intervention, participants have to choose whether they want to obtain further information about the course ore whether they are not interested in the course) Enrolment for informative event of the integrative cessation course (measured with enrolment lists)
9. Participation in the integrative cessation course (measured with enrolment lists)
10. Tobacco cessation attempt during past 8 weeks measured at t2
11. Cannabis cessation attempt during past 8 weeks measured at t2

Overall trial start date


Overall trial end date


Reason abandoned (if study stopped)


Participant inclusion criteria

1. Tobacco use at least once during past 30 days
2. Cannabis use at least once during past 6 months
3. No age constraints, either gender

Participant type


Age group




Target number of participants


Total final enrolment


Participant exclusion criteria

Does not meet inclusion criteria

Recruitment start date


Recruitment end date



Countries of recruitment


Trial participating centre

Swiss Research Institute for Public Health and Addiction ISGF

Sponsor information


Swiss Tobacco Prevention Fund (Switzerland)

Sponsor details

Federal Office of Public Health FOPH
Hessstrasse 27E

Sponsor type




Funder type


Funder name

Swiss Tobacco Prevention Fund (Switzerland), grant number 11.002932

Alternative name(s)

Funding Body Type

Funding Body Subtype


Results and Publications

Publication and dissemination plan

Not provided at time of registration

Intention to publish date

Participant level data

Not provided at time of registration

Basic results (scientific)

Publication list

2014 results in (added 19/09/2019)

Publication citations

Additional files

Editorial Notes

19/09/2019: The following changes have been made: 1. Publication reference added. 2. The final enrolment number has been added from the reference.