ACT is a behavioural approach, which has been referred to as one of the ‘new wave’ or ‘third generation’ cognitive behavioural therapies [670]. ACT applies six core processes (acceptance, cognitive defusion, being present, self as context, values, and committed action) to develop psychological flexibility – that is, the ability to remain in the present moment; be mindful of experiences, thoughts, emotions and sensations; and consciously behave in ways that align with chosen values [671]. Using mindfulness techniques, ACT is focused on addressing the reluctance to feel negative experiences, thoughts, emotions, and sensations, and accepting negative thoughts and feelings rather than striving to change or eradicate them. Strategies such as cognitive defusion ultimately help clients commit to and pursue their goals by encouraging clients to adopt a more non-judgemental and mindful approach to themselves and their surroundings [670].
ACT has been shown to be effective at reducing the quantity and frequency of AOD use [672–674], as well as associated stigma and shame [675]. It has been found to reduce psychiatric symptoms among people with single disorder anxiety [676, 677], OCD [678], depression [677, 679, 680], psychosis [681, 682], ADHD [683], and PTSD [684, 685]. Although evidence for ACT among people with co-occurring disorders is limited, ACT has been shown to improve abstinence among people with co-occurring affective disorders and AOD use [686], improve PTSD symptoms, and reduce frequency and quantity of AOD use among people with co-occurring PTSD and AOD use [687]. It has also been successfully adapted into e-health interventions [676, 679].