Lifetime rates of cannabis consumption are rising (Vogel et al, 2015; EMCDDA, 2018; SAMHSA, 2015), with both cannabis use and cannabis-use disorders being significantly more common in individuals with ADHD (Estévez et al, 2016). The aim of the present study was to assess whether the online self-help tool, CANreduce 2.0,* affects cannabis use and symptom severity in adults with ADHD compared with those without.

From August 2016 to December 2018, adult participants (aged ≥18 years, fluent in German) from the CANreduce 2.0 study (Baumgartner et al, 2021) with and without ADHD, who had used cannabis at least once weekly over the last 30 days, were included in this secondary analysis. Participants in the CANreduce 2.0 study had been randomised to two active arms with an adherence-focused, guidance-enhanced, web-based self-help intervention, with and without an eCoach, or a non-active arm (waiting-list controls), who had access to internet services as usual. The CANreduce 2.0 self-help intervention consists of eight modules, which are specifically designed to reduce cannabis consumption and common comorbid psychiatric conditions, such as ADHD, anxiety and depression:

• Modules 1 and 2 introduce the programme, with assistance in identifying situational and cognitive triggers which may lead to cannabis consumption.
• Modules 3–5 teach skills and techniques to enhance social relationships, restore sleeping patterns, deal with ruminations and help to develop the skills required to overcome cognitive and situational stimuli considered a relapse risk.
• Modules 6–8 teach social problem-solving and rejection skills, to help participants resist exceeding their daily cannabis intake goals. Additionally, these modules teach coping strategies and skills required to meet daily challenges, such as manifestations of depression. Upon completion, participants have the opportunity for a personalised review, using motivational interviewing techniques.

The primary outcome was change in cannabis consumption over a 30-day period compared with baseline and a 3-month follow-up assessment. The secondary outcomes were changes in the scores measured on the Severity of Dependence Scale (SDS^†), Cannabis Use Disorder Identification Test (CUDIT^‡), Adult ADHD Self-Report Scale (ASRS^§) v1.1, Centre for Epidemiologic Studies Depression (CES-D^||) scale, Generalised Anxiety Disorder (GAD^#) scale, and Post-traumatic Stress Disorder Short Screening Scale.** Additional outcomes were participant retention, level of adherence and side effects attributable to the programme.

In total, 367 participants with cannabis-use disorder were included in the analysis (n=94 with ADHD; n=273 without ADHD). Participants were predominantly male (263/367, 71.6%), with a mean age (standard deviation [SD]) of 27.9 (7.5) years, and were predominantly from Switzerland (140/367, 38.1%), Austria (134/367, 36.5%) and Germany (91/367, 24.7%). The mean (SD) age of participants when they started using cannabis was 20.0 (5.3) years, with a mean (SD) of 7.9 (6.7) years since the start of cannabis use. All participants scored higher than the CUDIT cutoff value (≥8) for cannabis-use disorder, with participants with ADHD scoring significantly higher than those without ADHD (p<0.001). Similarly, participants with ADHD scored significantly higher on the anxiety (p<0.001), depression (p<0.001) and post-traumatic stress disorder (p=0.005) scales.

Participants with and without ADHD reported a significant reduction in the number of days in the last month on which ≥1 joint was consumed (mean [SD] difference: 11.53 [21.87] and 8.53 [9.4], respectively; both p<0.001). Participants with and without ADHD also reported significant decreases in severity of dependence score (mean [SD] difference: 3.57 [3.65] and 2.47 [3.39], respectively; both p<0.001) and cannabis substance-use disorder score (mean [SD] difference: 6.38 [5.96] and 5.33 [6.05], respectively; both p<0.001).

Similar results were evident for anxiety GAD scores for participants with ADHD (mean [SD] difference 4.31 [4.71], p<0.001) and without ADHD (mean [SD] difference 1.84 [4.22], p<0.001), and for depression CES-D scores (with ADHD: mean [SD] difference 10.25 [10.54], p<0.001; without ADHD: mean [SD] difference 4.39 [10.22], p<0.001). However, the decrease in ASRS score was significant for participants with ADHD (mean [SD] difference 4.65 [4.44], p<0.001) but not for those without ADHD (mean [SD] difference 0.83 [4.10], p=0.19).

There were no significant changes from baseline to final follow-up in change in use, dependence, cannabis-use disorder, ADHD status, depression and anxiety.

Although baseline ADHD symptom severity was not associated with reduced cannabis consumption, severity of dependence or cannabis-use disorder scores, more severe symptoms of ADHD at baseline were associated with significantly greater reductions in depression (p<0.001) and anxiety (p<0.001) post-intervention.

There was a significant intergroup difference in retention at the final 3-month follow-up assessment, with fewer participants with ADHD having filled in their consumption diary than participants without ADHD (χ₁² = 5.21, p=0.02). However, there was no significant association between baseline ADHD symptom severity and retention rate. Similarly, there was no significant difference between the number of modules completed by participants with or without ADHD. There was also no significant association between the magnitude of decrease in ADHD symptoms and the number of completed modules.

Of the participants who completed the adverse effects questionnaire, the majority indicated no adverse effects, with one person stating that an adverse event had affected them to a great degree.

The authors identified several limitations of the study. Firstly, there were baseline differences between the two groups, including a higher number of days on which cannabis was used reported by participants with ADHD compared with those without ADHD. Secondly, the follow-up period of 3 months may have been too short to assess the efficacy of CANreduce 2.0. A longer follow-up may enable elucidation of the long-term benefits of the programme. Additionally, the study relied on a web-based assessment for ADHD, whereas a formal ADHD diagnosis would normally require at least one detailed face-to-face assessment.

The authors concluded that cannabis users with ADHD may benefit from CANreduce 2.0 to decrease the frequency and severity of cannabis dependence.

Read more about cannabis use in adults with ADHD and the efficacy of CANreduce 2.0 here

*CANreduce 2.0 has been specifically designed to enhance programme adherence, and achieve better outcomes, in individuals with certain psychiatric disorders such as ADHD, while providing better outcomes for depressed mood, problem-solving skills, rumination and sleeping habits
^†SDS score can range from 0 to 15, with a score >4 indicating cannabis dependence (Gossop et al, 1995)
^‡CUDIT scores can range from 0 to 40, with a score ≥8 indicating hazardous cannabis use and a score ≥12 indicating possible cannabis-use disorder (Adamson & Sellman, 2003)
^§Symptoms (cutoff score >14) reported using the ASRS v1.1 can range from 0 to 24 (Kessler et al, 2005)
^||CES-D scores can range from 0–60 (depression cutoff score >16) (Radloff, 1977)
^#GAD scale scores can range from 0–21, with cutoff score >10 (Spitzer et al, 2006)
**Post-traumatic stress disorder short screening scale score can range from 7–28, with a cutoff sum score of ≥4 suggesting post-traumatic stress disorder

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