The present study is a randomized controlled trial that will evaluate the effect of combining two treatment components (i.e., cognitive restructuring and detached mindfulness) drawn from cognitive behavioral therapies (CBTs) that are often combined in clinical practice. However, knowledge about the effect of combining these treatment components is lacking. Therefore, this study aims to explore single, combined, and sequencing effects of these two treatment components in patients with depression and/or anxiety disorders. Furthermore, the study aims to explore possible demographic and clinical moderators of the effects to address the question of what works for whom.

A relatively large proportion of psychotherapists endorse practicing eclectic or integrative therapy, drawing from different schools of therapy (Norcross & Alexander, 2019). This tendency towards integrative therapy has been expressed by former president of the Association of Cognitive and Behavioral Therapies, J. B. Persons, who writes: "We [clinicians] rarely proceed through a single protocol from beginning to end. Instead, we use what might be called a mix-and-match strategy, in which we select interventions or modules from one or even two or more protocols that we believe will be helpful to the patient" (Persons, 2005, p. 107). Indeed, there has been a growing research and clinical interest in personalized therapy where treatment components from different therapies are combined with the aim of targeting the symptomatology and theorized maintenance processes of the individual patient (Cohen et al., 2021; DeRubeis et al., 2014; Fisher et al., 2019; Fisher & Boswell, 2016; Hayes et al., 2022; Huibers et al., 2021; Sauer-Zavala et al., 2022). In addition to this, an increasing number of therapies are designed by combining components from different treatment models (e.g., modular and process-based therapies; Barlow et al., 2018; Hofmann & Hayes, 2019; Hofmann et al., 2021). As a result, patients are likely to be the recipients of several different techniques or strategies, based on different theoretical models, emphasizing different change principles. However, the extent to which compatibility exists between different treatment components remains an underexplored scientific question. The present study aims to fill this gap.

Combining cognitive behavioral therapies

Cognitive behavioral therapies (CBTs) are among the most well-researched psychological treatments for anxiety and depressive disorders (Cuijpers, 2017; Cuijpers et al., 2014). While CBT is often viewed as one of the major schools of psychotherapy, specific CBTs differ in their rationale and understanding of the key maintaining processes in psychopathology (Hayes, 2004). A core tenet of traditional CBT, also known as second-wave CBT, is that psychopathology is maintained by maladaptive or irrational thoughts (Beck, 1976). Thus, a commonly used therapeutic component derived from second-wave CBT is cognitive restructuring, where the patient is taught to think more realistically about emotion-evoking situations (Beck et al., 1979; Clark & Beck, 2010). Thus, cognitive restructuring can be said to target the content of thoughts.

In contrast, newer contemporary or so-called third-wave CBTs such as metacognitive therapy (MCT), acceptance and commitment therapy (ACT), and mindfulness-based cognitive therapy (MBCT) target thought processes (Hayes, 2004). A commonly used therapeutic component across third-wave CBTs involves teaching the patient to meet their experiences with mindfulness and acceptance rather than attempting to change their form (termed detached mindfulness in MCT, defusion in ACT, and decentering in MCT; Hayes et al., 2012; Segal et al., 2002; Wells, 2009). Thus, it can be argued that second- and third-wave CBTs reflect very different ways of approaching one's inner life.

Despite the differences between second- and third-wave CBTs, treatment components from each wave are often combined. One example of this is the widely employed Unified Protocol (UP) which is a transdiagnostic modular cognitive-behavioral treatment for emotional disorders (e.g., anxiety and depression) (Barlow et al., 2018). In UP, patients are asked to engage in cognitive restructuring (within the treatment module of cognitive flexibility) in one module and to practice detached mindfulness (within the treatment module of mindful emotion awareness) in another (Barlow et al., 2018). Several studies have documented that UP is an effective treatment for anxiety and depression (Longley & Gleiser, 2023). However, since the treatment modules in UP are rooted in different therapeutic traditions with different rationales, an intriguing question remains whether the treatment modules are in fact compatible. If not, then it is possible that UP is effective not because but rather despite the combination of the treatment modules (O'Toole et al., 2024).

Compatibility of components

Regarding the combination of mindful emotion awareness and cognitive flexibility, it is theoretically plausible that these modules might be incompatible since the technique of noticing and accepting one's thoughts/emotions (in the module mindful emotion awareness) could be argued to be in opposition to the technique of actively changing one's thoughts (in the module cognitive flexibility). This notion is supported by a small study (N=12) by Gkika and Wells (2015) which investigated the effect of cognitive restructuring and detached mindfulness in an anxiety-provoking situation in patients with elevated symptoms of social anxiety. They found that each technique alone reduced symptoms of social anxiety. However, when combined, a sequencing effect emerged where detached mindfulness followed by cognitive restructuring, but not the reverse, led to increased anxiety (Gkika & Wells, 2015). Borlimi et al. (2019) similarly demonstrated a sequencing effect. They asked non-clinical participants (N=35) to recall an unpleasant experience and apply either cognitive restructuring or an acceptance technique. Acceptance reduced sympathetic reactivity (i.e., galvanic skin response) more than cognitive restructuring, and importantly, the effect was significantly larger when acceptance followed cognitive restructuring than vice versa (Borlimi et al., 2019).

The studies by Gkika and Wells (2015) and Borlimi et al. (2019) are both laboratory experimental studies. The question thus remains whether and how their findings can be generalized to a clinical context with longer duration of each treatment component. Only one larger intervention study exploring combinatory and sequencing effects exists. In this study, Brose et al. (2023) investigated the effect of internet-based cognitive restructuring and behavioral activation on symptoms of depression delivered over 6 weeks. Individuals with mild to moderate depressive symptoms (N=2,304) were randomized to one of two treatment arms, one receiving behavioral activation followed by cognitive restructuring, the other vice versa. The groups had similar dropout rates and showed similar improvements over time, indicating no incongruency between those two components. Besides differences in size and setting (experimental vs. actual treatment), the study by Brose et al. (2023) also differs from the other clinical studies by testing a "cognitive" component against a "behavioral" component instead of comparing different "cognitive" components (e.g., cognitive restructuring and detached mindfulness) against each other. In this case, the rationales may be more consistent with each other.

Taken together, the research findings described above, coupled with results from the few other available studies of combinatory effects (Dibbets et al., 2012; Woelk et al., 2022), testify that combining otherwise effective stand-alone treatment components 1) does not necessarily yield an additive effect, 2) may even sometimes detract from a positive outcome, and 3) that the combined effect may depend on the order of the components. Thus, to be able to combine different treatment components for anxiety and depression effectively, there is a need for intervention studies examining single, combined, and sequencing effects for treatment components from different therapies that are often combined. Currently, such research is sparse, thereby motivating the present study. Moreover, understanding for whom these effects are likely to occur is important for the appropriate adaptations of therapeutic interventions to fit the needs of the individual patients (i.e., personalized therapy; Cohen et al., 2021).

Aims and hypotheses

The primary aim of the present study is to explore the effect of combining treatment components drawn from different CBTs. Thus, we will explore single, combined, and sequencing effects of two treatment modules (i.e., mindful emotion awareness and cognitive flexibility). These modules are routinely delivered together in UP for patients with anxiety disorders or MDD. It is hypothesized that both mindful emotion awareness and cognitive flexibility, when delivered individually, will be effective in reducing symptoms of anxiety and depression. The study will take an exploratory stance regarding combined and sequencing effects and will explore if combined effects are best understood as non-additive, additive, synergistic or antagonistic (cf. O'Toole et al., 2024).

A secondary aim of the study is to explore possible demographic and clinical moderators of the effects (e.g., primary diagnosis, baseline cognitive function and symptomatology) to address the question of what works for whom.

Inclusion Criteria:

1. Age ≥ 18 years.
2. A diagnosis of an anxiety disorder (generalized anxiety disorder, social anxiety disorder, or panic disorder with or without agoraphobia) and/or mild to moderate major depressive disorder (MDD) according to DSM-5 (American Psychiatric Association, 2022).
3. Danish language proficiency.
4. Ability and willingness to give informed consent.
5. No or stable antidepressant/antianxiety medication (i.e., same dosage for ≥ 8 weeks).
6. Access to either a smartphone, tablet, or computer with video camera.

Exclusion Criteria:

1. Severe depression deemed to require more intense psychotherapy or medication.
2. Persistent depressive disorder (i.e., depressive symptoms have persisted for 2 years or more).
3. Non-stabilized medication (see above).
4. Currently receiving other psychotherapy or counseling.
5. Not capable of participating online.
6. Lack of Danish proficiency.
7. A history of bipolar disorder.
8. Current or past psychosis.
9. Substance abuse or dependence judged to require treatment.
10. Suicide risk requiring immediate hospitalization.

It will not be known to participants that we are testing combinatory and sequencing effects and that participants are randomly allocated to receive the treatment modules in a specific order.