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Internet-based self-help intervention helped reduce cannabis use, disorder

An internet-based self-help intervention with an impersonal service team “significantly reduced cannabis use, cannabis-use disorder, dependence severity and general anxiety symptoms” among people wanting treatment, reports an international team of researchers led by the University of Zurich in Switzerland.

Other institutions involved were the Institute for Addiction Prevention, Addiction and Drug Coordination Vienna in Austria; the University of Basel, University of Bern and Arud Centre for Addiction Medicine in Switzerland; Technical University Munich in Germany; and York University in Toronto.

The following is the introduction to the study article published in the Journal of Medical Internet Research on 30 April 2021, followed by the article abstract.

Cannabis is the most consumed illicit drug in Europe, having witnessed a steady increase in recent years, evidenced by roughly 24.7 million European users in 2019. The global number of cannabis users was estimated as 178 million people in 2017.

As more and more countries consider decriminalisation or outright legalisation, it seems unlikely that the increase in cannabis users will stagnate soon.

Only a minority of cannabis users seem to develop cannabis dependence; in general population surveys, the risk of becoming dependent on cannabis appears to be between 10% and 11% of all cannabis users.

However, for cannabis users who start at a young age, the risks of cannabis dependence and cannabis use problems are significantly higher. In addition, poorer mental and physical health, lower educational attainment, and reduced cognitive performance than non-cannabis users are common among daily cannabis users.

Numerous studies also point to a broad range of often co-occurring mental health disorders, such as depression, anxiety and posttraumatic stress disorder, during the treatment of problematic cannabis use.

Treatment demand in Europe for first-time admissions with cannabis listed as the main problem substance has been increasing steadily, having almost doubled from roughly 45,000 in 2006 to approximately 83,000 in 2017.

However it is clear that, although the number of clients seeking treatment has increased, they still account for just a small minority of cannabis users who could potentially benefit from treatment, with or without comorbid mental health problems.

Similarly, only a few consumers seek professional medical assistance, suggesting that a broader range of treatment options should be provided. Various potential barriers prevent people from seeking treatment, including poor accessibility to treatment centres, the lack of awareness of negative health consequences, the wish to reduce cannabis use on their own, and fear of stigmatisation as a drug addict, which seems to be a major factor.

Facilitators of treatment, on the other hand, include improving available information, increased access to cannabis-specific services, providing additional treatment options, and making admissions easier, all of which many internet-based interventions could provide.

Studies on web-based interventions for which participants were recruited from the general adult population (>18 years old) have been shown to draw a cannabis-using population that is different than those entering outpatient addiction treatment centres, not only in terms of having a higher level of education and being older, but also in terms of reporting more frequent cannabis use.

However, poor adherence to the intervention is often found in these studies. Moreover, a recent meta-analysis on internet-based treatments for cannabis users yielded significant but only small effect sizes for the reduction of cannabis use (mostly frequency) in the short term (15 comparisons, Hedges g=0.12) that could not be maintained longer term (12 months).

The effects of multisession interventions, such as those combining cognitive behavioural therapy with motivational interviewing, produced larger effect sizes (6 comparisons, Hedges g=0.18) than single-session interventions using approaches like brief interventions and motivational interviewing (13 comparisons, Hedges g=0.09).

Among the studies assessing multisession interventions, only 2 took symptoms of possible co-occurring mental health disorders into account.

In previous studies, called CANreduce 1.0, we were able to show that additional professional chat sessions increased the effectiveness of an internet-based self-help programme designed to reduce cannabis use.

The study also found that participants who had the opportunity but did not participate in these chat sessions, nevertheless reduced their cannabis use more than those who only received internet-based self-help from the beginning.

It seems that, on its own, having a professional therapist send chat invitations helped to reduce cannabis use in cannabis users.

Since only a quarter of the participants in the treatment arm with chat took part in at least one chat appointment, we wondered whether the same effect could be achieved by replacing the professional therapist with a virtual eCoach.

We also found that almost half (44.8%) of participants screened positive for clinically relevant depression symptoms at baseline. Comorbidity of depressive symptoms and substance use and its hindrance on positive treatment outcomes has repeatedly been demonstrated.

CANreduce 2.0, a minimally guided internet-based self-help intervention for cannabis users, is designed to overcome the issues of low intervention adherence and effectiveness, as well as to address frequently co-occurring mental health disorders.

This intervention is based on adherence-focused guidance which has, to date, never been tested as a component of an internet intervention for individuals with a substance use disorder but has been documented to be effective at increasing adherence to web-based self-help for the reduction of stress and depression symptoms.

The concept of adherence-focused guidance enhancement is primarily based on the supportive-accountability model of guidance in web-based interventions, which argues that adherence to internet-based interventions relies on an online coach (eCoach) who is seen as trustworthy, benevolent and having expertise, and who has clear, process-oriented expectations in a reciprocal eCoach-participant relationship.

In addition to an eCoach, we incorporated cognitive behavioral therapy–based approaches into the programme to target issues that potentially help to ameliorate overlapping common mental disorder symptoms, such as inactivity, depressed mood, excessive rumination, and difficulty relaxing.

The primary goal of this study was to investigate whether intervention effectiveness and program adherence can be increased by implementing adherence-focused guidance and emphasizing the social presence factor of a personal eCoach when compared with a general support team implementation.


Study details

CANreduce 2.0 Adherence-Focused Guidance for Internet Self-Help Among Cannabis Users: Three-Arm Randomized Controlled Trial

Christian Baumgartner, Michael Patrick Schaub, Andreas Wenger, Doris Malischnig, Mareike Augsburger, Marc Walter, Thomas Berger, Lars Stark, David Danied Ebert, Matthew T Keough and Severin Haug.

Author affiliations: Swiss Research Institute for Public Health and Addiction, University of Zurich; Institute for Addiction Prevention, Addiction and Drug Coordination Vienna; University of Basel; University of Bern; Arud Centre for Addiction Medicine, Zurich; Technical University Munich; and York University in Canada.

Published in the Journal of Medical Internet Resarch, Volume 23, No 4 (2021), on 30 April 2021.



Despite increasing demand for treatment among cannabis users in many countries, most users are not in treatment. Internet-based self-help offers an alternative for those hesitant to seek face-to-face therapy, though low effectiveness and adherence issues often arise.


Through adherence-focused guidance enhancement, we aimed to increase adherence to and the effectiveness of internet-based self-help among cannabis users.


From July 2016 to May 2019, cannabis users (n=775; male: 406/575, 70.6%, female: 169/575, 29.4%; age: mean 28.3 years) not in treatment were recruited from the general population and were randomly assigned to (1) an adherence-focused guidance enhancement internet-based self-help intervention with social presence, (2) a similar intervention with an impersonal service team, and (3) access to internet as usual. Controls who were placed on a waiting list for the full intervention after 3 months underwent an assessment and had access to internet as usual.

The primary outcome measurement was cannabis-use days over the preceding 30 days. Secondary outcomes included cannabis-dependence severity, changes in common mental disorder symptoms, and intervention adherence.

Differences between the study arms in primary and secondary continuous outcome variables at baseline, posttreatment, and follow-up were tested using pooled linear models.


All groups exhibited reduced cannabis-use days after 3 months (social presence: –8.2 days; service team: –9.8 days; internet as usual: –4.2 days).

The participants in the service team group (P=.01, d=.60) reported significantly fewer cannabis-use days than those in the internet as usual group; the reduction of cannabis use in the social presence group was not significant (P=.07, d=.40). There was no significant difference between the 2 intervention groups regarding cannabis-use reduction.

The service team group also exhibited superior improvements in cannabis-use disorder, cannabis-dependence severity, and general anxiety symptoms after 3 months to those in the internet as usual group.


The adherence-focused guidance enhancement internet-based self-help intervention with an impersonal service team significantly reduced cannabis use, cannabis-use disorder, dependence severity, and general anxiety symptoms.


CANreduce 2.0 Adherence-Focused Guidance for Internet Self-Help Among Cannabis Users: Three-Arm Randomized Controlled Trial (Open access)




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