Evidence 

Theory of Change  

ACT is based on modern behavioural psychology, including Relational Frame Theory. It applies mindfulness and acceptance processes (i.e. acceptance, defusion, contact with the present moment, and self as context), and commitment and behaviour change processes (i.e. contact with the present moment, self as context, values, and committed action) to achieve psychological flexibility. Psychological flexibility acts to counter experiential avoidance and ineffective coping, thereby modifying the impact of potentially limiting life experience(s), and its associated symptoms. A full list of a full list of all the RCT’s in ACT published from 1986 to March 2022 are available on the contextual science site: https://contextualscience.org/act_randomized_controlled_trials_1986_to_present. The evidence relating to topics where ACT is recommended in The Matrix are summarised below. 

Research Design & Number of Studies 

Adult Evidence for Chronic Pain 

The best available evidence for ACT in the management of chronic pain in adults comes from meta-analyses and randomised controlled trials (RCTs). Some of these studies are described below.  

A recent comprehensive meta-analysis included in-person and internet delivered ACT for adults with chronic pain (Lai et al. 2023). Thirty-three RCTs, including 2293 participants were included, and participants in these studies presented with different types of pain including mixed chronic pain conditions, fibromyalgia, and chronic headaches.  

A previous meta-analysis of RCTs evaluated the effectiveness of internet/ online delivered ACT in adults (18+ years) with chronic pain (i.e., pain lasting three or more months), or with a diagnosis of a chronic pain condition (Gandy et al., 2022). 36 RCTs (n=5778) were included, and participants in these studies presented with different types of pain including mixed chronic pain condition, back pain, fibromyalgia, arthritic conditions, and peripheral neuropathy. The studies were conducted in countries in Europe, North America (i.e. Canada, USA) and Australia.  

An earlier meta-analysis of RCTs included studies conducted in adults (≥16 years) with chronic pain for at least 3 months (Hughes et al., 2017). Pain could be anywhere, but it excluded headache and pain associated with malignant disease. Eleven RCTs (n=863) were included, of which nine studies were conducted in Europe, and two studies were conducted in the United States. ACT interventions included guided internet, individual, manual-based self-help, and ACT delivered in group format. No restrictions were made for the comparator.  

An RCT investigating online groups included 302 adults (aged ≥ 18 years) who were randomly assigned to receive ACT group or to a waiting-list control group (Lin et al., 2017). ACT was delivered as ACTonPain, an internet/ mobile-based program, delivered over 1-hour every week for 8 weeks. ACT was delivered with or without therapist guidance. Participants were expected to have sufficient knowledge of German, and should have experienced chronic pain for at least 6 months.  

Another RCT investigating guided internet delivered ACT was conducted Netherlands, and included 238 adults, aged ≥ 18 years, with chronic pain ≥ 3days per week for ≥6 months (Trompetter et al., 2015). Participants were randomly assigned to receive ACT, as a guided internet delivered intervention, or to control conditions of expressive writing or waiting list. ACT consisted of nine modules, which could be completed over 9–12 weeks, in approximately ≥3 hours per week. 

A different RCT compared the efficacy of physical therapy informed by ACT (PACT) against standard care physical therapy (Godfrey et al., 2020). The study was conducted in London, UK, and included 284 adults (aged ≥18 years) with nonspecific chronic lower back pain with or without associated leg pain, of greater than 12 weeks’ duration.  PACT was delivered as a brief physical therapy intervention, and consisted of 3 individual treatment sessions delivered over 1.5 months in two 60-minutes face-to-face sessions and one 20-minute telephone call. 

A further two studies (Scott et al., 2017) and Wetherell et al., (2011) specifically investigated ACT for people over 65 with longstanding pain with significant distress and disability. and found …  

Outcomes Achieved 

Adult Outcomes for Chronic Pain 

Compared to waiting-list control and treatment-as-usual groups, the following outcomes were observed; 

• Significantly increased pain acceptance at post-treatment (Hughes et al., 2017), sustained at follow-up (i.e. at 6-months post-randomisation for the Lin et al., 2017 study)  
• Significantly reduced pain interference at post-treatment (Gandy et al., 2022; Lin et al., 2017), sustained at 6-months post-randomisation (Lin et al., 2017)  
• Significantly reduced pain intensity and pain catastrophising at post-treatment (Lai et al., 2023; Gandy et al., 2022). Effects on pain catastrophising was sustained at 3 and 6-months follow-up (Trompetter et al., 2015). Effects on pain intensity were reported at 6 months follow-up (Trompetter et al., 2015).  
• Significantly improved functioning at post-treatment (Godfrey et al., 2020), sustained at 3 months follow-up (Hughes et al., 2017)  
• Significantly reduced anxiety (Lai et al., 2023; Gandy et al., 2022; Hughes et al; 2017) and depression symptoms (Gandy et al., 2022; Lin et al., 2017; Hughes et al., 2017) at post-treatment. Effect on depression were observed at follow-up (i.e. at 3 months for Hughes et al., 2017; at 6-months for Lin et al., 2017 study; at 6-months follow-up for Trompetter et al., 2015)  
• Significantly improved psychological flexibility at post-treatment and 3-months follow-up (Hughes et al., 2017; Trompetter et al., 2015), and at 6 months (Trompetter et al., 2015)  
• Significantly improved self-efficacy at post-treatment (Gandy et al., 2022)  
• Significantly better physical health and treatment credibility (Godfrey et al., 2020)  
• Face-to-face ACT yielded significantly larger effects on physical outcomes than internet-delivered ACT (Lai et al., 2023)  
• Significant improvements in mental health and disability post-treatment in older adults (Scott et al. 2017). 

Adult Evidence for Generalised Anxiety Disorder (GAD) 

Some of the best available evidence for ACT in the treatment of GAD includes four Randomised Controlled Trials (RCTs). 

One of these RCTs was conducted in USA, and included 128 adults (aged 19-60 years) with mixed anxiety disorders (i.e. with a diagnosis of one or more anxiety disorders, including panic disorder with or without agoraphobia, social anxiety disorder, specific phobia, obsessive-compulsive disorder, or generalized anxiety disorder) (Arch et al., 2012). The study compared the effectiveness of ACT to CBT. ACT was delivered over twelve weeks, in 1-hour weekly individual therapy sessions, based on a detailed treatment manual. 

Another RCT was conducted in Brazil, and included in 92 adults (aged 18-65 years) diagnosed with GAD (de Almeida Sampaio et al., 2020). The study compared the effectiveness of ACT to standard non-directive supportive group therapy. ACT was delivered in group format, over ten 2‐hr sessions, and one follow‐up session at 3 months posttreatment.    

The third RCT was conducted in Sweden and included 103 adults (≥18 years) diagnosed with GAD (Dahlin et al., 2016). The study compared the effectiveness of therapist-guided internet-delivered Acceptance-Based Behaviour Therapy (ABBT) to a waiting-list control group. The intervention consisted of seven online modules, with one module completed per week in a predetermined order. Participants were given a total time of nine weeks to complete the program.  

The fourth was a single blind cluster RCT that was conducted in the Netherlands, and included 314 older adults (aged 55-70 years) with mild to moderately severe anxiety symptoms (Witlox et al., 2021). The study compared the effectiveness of blended ACT to face-to-face CBT. Blended ACT consisted of 9 lessons on the web-based ACT-module, completed over 9-12 weeks, and 4 face-to-face sessions mental health counsellor.  

Adult Outcomes 

• Significantly improved anxiety specific outcomes (Dahlin et al., 2016; Arch et al., 2012) and depression outcomes (Dahlin et al., 2016). Improvements were observed at post-treatment (Dahlin et al., 2016; Arch et al., 2012), sustained at 6-months (Dahlin et al., 2016) and at 12- months follow-up (Arch et al., 2012). Improvements in the ACT group were equivalent to the CBT group (Arch et al., 2012) 
• Significantly more rapid rate of change for measures of stress, clinical severity, anxiety and worry, at post-treatment. There was significantly better maintenance in measures of general clinical severity at 3-months follow-up (de Almeida et al., 2020) 
• Significantly reduced anxiety symptoms at post-treatment for within group analysis. Effects were maintained at 12-months follow-up and was comparable to the CBT group (Witlox et al., 2021) 
• Significantly increased positive mental health at post-treatment, maintained at 12-months follow-up (Witlox et al., 2021) 

Child and Young People (CYP) Evidence for Chronic Pain 

Some of the best available evidence in CYP includes two Randomised Controlled Trials (RCTs) and one non-randomised pilot trial.  

The first of these RCTs included 32 children in Sweden, aged between 10 and 18 years (Wicksell et al., 2008). Participants had been suffering with pain that had lasted more than 3 months and were randomised to receive ACT or multidisciplinary treatment approach including amitriptyline. The different types of pain participants presented with included headache, back and/ or neck pains, widespread musculoskeletal pain, complex regional pain syndrome, and visceral pain. ACT was individually delivered to participants, over 10 weekly sessions, each lasting about 60 minutes. Parents received 1–2 sessions, each lasting about 90 minutes.  

The second study was conducted in Iran and included 20 children aged 7-12 years (Ghomian et al., 2014). Participants had been suffering with the chronic pain for at least 6 months. This included pain from rheumatoid disease, chest pain, leg pain, and kidney pain. Participants were randomised to the ACT or control group, however details regarding treatment format or the control condition were not provided.  

The third was a pilot study that included 28 self-recruited adolescents in Sweden, aged 13–17 years (Zetterqvist et al., 2020). Participants had been suffering with chronic pain for at least 3 months. The participants received 8 weeks of internet-delivered ACT, while parents received an 8-week internet-delivered parental programme. Both interventions were delivered as responsive web applications intended for smartphone use, and were supported by a therapist.   

Children and Adolescent Outcomes for Chronic Pain 

• Significantly greater improvement in pain-related functioning and reduction in pain interference at post-treatment (Zetterqvist et al., 2020; Wicksell et al., 2008). Effect on pain-related functioning sustained at a mean follow-up period of 6.8 months (Wicksell et al., 2008) 
• Significantly better health-related quality of life at post-treatment (Wicksell et al., 2008; Ghomian et al., 2014), sustained at 5 months follow-up (Ghomian et al., 2014)  
• Significant decrease in kinesiophobia, pain-related intensity and pain-related discomfort at post-treatment. Effect on pain-related intensity and discomfort were sustained at a mean follow-up period of 6.8 months (Wicksell et al., 2009) 
• Significantly reduced psychological inflexibility, depressive symptoms and insomnia severity at post-treatment and follow-up at 17-25 weeks (Zetterqvist et al., 2020) 

Parent Outcomes for Chronic Pain 

• Significantly reduced pain reactivity at post-treatment and at 17-25 weeks follow-up (Zetterqvist et al., 2020) 
• Significantly reduced anxiety and depression symptoms at post-treatment and at 17-25 weeks follow-up (Zetterqvist et al., 2020) 
• Significantly increased psychological flexibility at post-treatment and at 17-25 weeks follow-up (Zetterqvist et al., 2020) 

Children Evidence for Anxiety 

One of the best available evidence for ACT in the treatment of anxiety in children includes a Randomised Controlled Trial (RCT) conducted in Australia (Hancock et al., 2018; 2016). The study included 193 children and adolescents diagnosed with anxiety disorder. Participants, aged 7-17 years, were block-randomized to a 10-week 1.5-hour group-based program of ACT or CBT or a 10-week waitlist control (WLC). Sessions were attended by parents and children.    

Children Outcomes 

Compared to waitlist control, the following outcomes were observed for ACT; 

• Significantly lower anxiety disorder diagnosis and clinical severity at post-treatment, maintained at 3 months, and 2-years follow-up (Hancock et al., 2018; 2016) 
• Significantly lower anxiety scores at post-treatment, maintained at 3-months and 2-years follow-up (Hancock et al., 2018; 2016) 
• Significantly lower child anxiety life interference scores at post-treatment, maintained at 3-months and 2-years follow-up (Hancock et al., 2018; 2016) 
• Significantly improved quality of life at post-treatment, maintained at 3 months follow-up (Hancock et al., 2018; 2016