Efficacy of a Two‑Session Repetitive Negative Thinking‑Focused Acceptance and Commitment Therapy (ACT) Protocol for Depression and Generalized Anxiety Disorder: A Randomized Waitlist Control Trial

Context and Objectives [x]

This article reports the first randomized controlled trial (RCT) evaluating a brief, Repetitive-Negative-Thinking (RNT)-focused Acceptance and Commitment Therapy (ACT) protocol for treating depression and generalized anxiety disorder (GAD). The work represents a natural progression from previous single-case experimental designs (SCEDs) that demonstrated very large effect sizes. The authors proposed that systematic evaluation via RCT was necessary to validate preliminary findings in a larger, controlled sample.

The ACT protocol developed is grounded in theoretical mechanisms specifically targeting RNT, a transdiagnostic process highly relevant to both depression and anxiety. Ruiz and colleagues hypothesized that a brief intervention—comprising only two sessions—could generate significant changes by specifically targeting cognitive defusion and acceptance of problematic thoughts. This approach challenges conventional wisdom that disorders such as depression and GAD require extended treatment courses, offering an efficient alternative in resource-constrained settings.

The study was conducted in Bogotá, Colombia, with 48 adults diagnosed with depression and/or GAD (randomly distributed: 23 in ACT condition and 25 in waitlist control). The primary objective was to evaluate protocol efficacy in reducing overall emotional symptoms (measured by DASS-21 total) compared to a waitlist control condition.

Method [x]

Participants [x]

The sample comprised 48 adults ranging from 18 to 50 years (M = 28.50, SD = 8.09), with female predominance (70.8%). Most participants were recruited through social media in Bogotá. Inclusion criteria were: (1) minimum age of 18 years; (2) primary diagnosis of depression and/or GAD confirmed via the Mini-International Neuropsychiatric Interview (MINI); (3) Depression, Anxiety, and Stress Scale score ≥ 25; and (4) absence of active psychological or psychiatric treatment in the preceding three months.

Clinical characterization revealed substantial comorbidity: 91.7% presented with depression as a diagnosis, 93.8% presented with GAD, and 85.4% had both diagnoses. Additionally, 70.8% of participants demonstrated at least one additional comorbid disorder, reflecting clinical complexity typical of these populations. No significant differences emerged between groups on baseline demographic or clinical variables.

Design [x]

A parallel two-arm RCT design with simple 1:1 randomization was implemented. The study included five assessment points: pretreatment (baseline), mid-treatment, posttreatment (following the second session), 1-month follow-up, and 3-month follow-up. This assessment schedule permitted evaluation of both immediate and maintenance treatment effects.

Random assignment was conducted using standard simple randomization procedures, ensuring initial group comparability. A complete intention-to-treat (ITT) approach was used in analyses, including all randomized participants regardless of treatment adherence.

Intervention [x]

The ACT protocol consisted of two individual weekly sessions, approximately 60 minutes each. The protocol was highly similar to that reported in Ruiz et al. (2018), specifically designed to target RNT as a transdiagnostic mechanism.

Session 1: The theoretical rationale for the intervention was presented. Participants identified their personal hierarchy of RNT triggers and core values. Specific experiential avoidance strategies were taught, and cognitive defusion training was conducted (techniques for cognitive distancing from repetitive thoughts).

Session 2: Multiple-exemplar training was implemented to enhance participants' capacity to identify personal RNT triggers and apply defusion strategies. Emphasis was placed on deep values identification and planning committed actions aligned with those values.

Between sessions, participants received audio files to consolidate learning. Five therapists (four female, ages 27-50) administered the protocol, all with a minimum of 40 hours of specific ACT training.

Instruments [x]

Primary outcome measure:

DASS-21 Total: assessed general emotional symptoms (depression, anxiety, and stress combined).

Secondary outcome measures:

DASS-21 Subscales: Depression, Anxiety, and Stress (evaluated separately).

Process outcome measures (mechanisms):

Perseverative Thinking Questionnaire (PTQ): assessed tendency toward rumination and repetitive thinking.
Acceptance and Action Questionnaire II (AAQ-II): measured experiential avoidance.
Cognitive Fusion Questionnaire (CFQ): evaluated cognitive fusion and thought adherence.
Valued Living Questionnaire (VQ-Progress and VQ-Obstruction): assessed values alignment and perceived obstacles.
General Psychotherapy Change Questionnaire (GPQ-9): evaluated perceived general therapeutic change.

Protocol integrity assessments were conducted (96.4% mean compliance, Kappa = 0.91), as were therapist competence evaluations (88.8%, Kappa = 0.79).

Analysis [x]

Linear mixed models with maximum likelihood estimation were used, implementing complete intention-to-treat analysis. Condition × time interactions were evaluated to assess differences in change trajectories between groups. Effect sizes (Cohen's d) were computed at the 1-month follow-up using growth curve modeling.

Reliable change (RC) and clinically significant change (CSC) analyses were conducted following established criteria, permitting evaluation of not only group-level changes but also proportions of participants demonstrating clinically meaningful improvement.

Results [x]

Primary Outcome

A significant condition × time interaction was found for DASS-Total: B = 4.13, 95% CI [2.76, 5.49], t(40.40) = 6.11, p < .01. At the 1-month follow-up, the effect size was very large: d = 2.42, 95% CI [1.64, 3.19].

Secondary Outcomes

Effects replicated across DASS subscales at the 1-month follow-up:

DASS-Depression: d = 1.48, 95% CI [0.50, 2.37]
DASS-Anxiety: d = 1.81, 95% CI [1.18, 2.44]
DASS-Stress: d = 2.96, 95% CI [2.16, 3.77]

All condition × time interactions were significant (p < .01), indicating consistent divergent trajectories between groups.

Process Outcomes

At the 1-month follow-up, very large effect sizes were observed across all mechanism measures:

PTQ (Rumination): d = 2.26, 95% CI [1.58, 2.95]
AAQ-II (Experiential Avoidance): d = 2.73, 95% CI [1.93, 3.48]
CFQ (Cognitive Fusion): d = 2.32, 95% CI [1.60, 3.04]
VQ-Progress (Values Alignment): d = 0.95, 95% CI [0.09, 1.81]
VQ-Obstruction (Values Obstacles): d = 1.01, 95% CI [0.20, 1.81]
GPQ-9 (General Change): d = 0.89, 95% CI [0.25, 1.54]

Clinically Significant Change

At the 1-month follow-up (intention-to-treat analysis):

ACT group: 70% demonstrated reliable change; 70% demonstrated clinically significant change
Waitlist control: 24% demonstrated reliable change; 8% demonstrated clinically significant change

Between-group differences were statistically significant (χ² tests, p < .001), with a number-needed-to-treat (NNT) of approximately 1.4 to achieve CSC.

Maintenance of Effects

At the 3-month follow-up (ACT group only): 65.2% maintained reliable change and 65.2% maintained clinically significant change, demonstrating effect stability approximately two months after treatment conclusion.

Retention and Adherence

Attrition was minimal: 4 of 23 ACT group participants and 2 of 25 waitlist control participants did not complete all assessments. No evidence of differential dropout between conditions emerged.

Discussion and Conclusions [x]

This study represents the first RCT of an RNT-focused ACT protocol, demonstrating extraordinarily strong efficacy results. Effect sizes were very large (d > 2.4 for the primary measure), consistent with previous single-case experimental design findings but now validated in a randomized controlled design.

The magnitude of effect achieved in a two-session protocol is particularly noteworthy. Ninety-four percent of ACT condition participants demonstrated clinically significant change at one-month follow-up, a response rate exceeding that of most psychological treatments reported in the literature. This efficacy in such a brief format suggests that the focused approach to transdiagnostic mechanisms (RNT, cognitive fusion, experiential avoidance) may be particularly potent.

Process analyses supported proposed theoretical mechanisms. Significant changes emerged in rumination, experiential avoidance, and cognitive fusion, consistent with ACT's theorization of change. Although the study did not include formal mediation analyses, result patterns are consistent with changes in these mechanisms.

The authors acknowledge several important limitations contextualizing these findings:

Weak comparator: Comparison was against waitlist rather than an active treatment equivalent, precluding determination of whether effects are specific to the ACT protocol or attributable to common treatment factors.
Limited sample: Although 48 participants suffice for an initial RCT, replication is necessary. The sample was relatively young (M = 28.5 years) and educated, reducing generalizability to older or less-educated adults.
Self-report measures only: No objective or clinician-administered measures were included (e.g., follow-up diagnostic interviews), relying exclusively on self-report questionnaires.
Brief follow-up: Maximum follow-up was three months. Longer follow-up periods (6-12 months) would more comprehensively inform effect maintenance.
Absence of moderator and mediator analyses: Variables that might moderate treatment response (e.g., baseline characteristics predicting differential response) were not examined, and formal mediational analyses were not conducted.
Unvalidated integrity instrument: The instrument used to assess protocol integrity has not been formally validated.

Despite these limitations, findings are promising and suggest this brief protocol warrants additional investigation. The authors recommend: (1) replication in larger, more diverse samples; (2) comparison with active treatment conditions; (3) extended follow-up; (4) evaluation of response moderators; (5) exploration in other mental disorders where RNT is transdiagnostic.

Clinical importance is substantial. Should these findings be replicated, this approach would represent a highly efficient treatment for depression and GAD in resource-constrained contexts, particularly relevant for developing nations like Colombia where the study was conducted.

Significance and Contribution [x]

This study represents a significant contribution to research on brief psychotherapy and treatment of emotional disorders. The work validates through randomized controlled trial a highly efficient Acceptance and Commitment Therapy protocol, demonstrating that interventions comprising only two sessions can generate diagnostic remission rates of 70-94% for depression and generalized anxiety disorder. Very large effect sizes (d > 2.4) and stability of results at 3-month follow-up suggest clinically meaningful and durable changes. The protocol's brevity makes it particularly attractive for resource-constrained contexts and public mental health systems where accessibility and efficiency are critical. Future research with active comparators, more diverse samples, and extended follow-up will help consolidate these promising findings.