This study tested a 4-week, internet-based Mindfulness-Based Cognitive Therapy (MBCT) program designed to help people experiencing adjustment disorder during the COVID-19 pandemic. Adjustment disorder is a stress-related condition that can cause anxiety, depression, and difficulty coping after major life changes.

We compared the online MBCT program to two other groups: an internet-based relaxation training program and a wait-list group. A total of 301 adults from Poland took part. We measured symptoms of adjustment disorder, depression, and anxiety before the program, right after, and one month later.

Results showed that the online MBCT program led to greater improvements in depression and anxiety than the other two groups. People in MBCT also developed more self-compassion and were better able to distance themselves from unhelpful thoughts, which helped reduce their symptoms. Benefits lasted at least one month after the program ended.

These findings suggest that a brief, self-guided, online mindfulness program can be an effective, accessible way to support mental health during stressful times such as a pandemic.

Background and Rationale Adjustment disorder (AjD) is a stress-related mental health condition characterized by maladaptive emotional and behavioral responses to an identifiable stressor. Core symptoms include persistent preoccupation with the stressor and difficulty adapting, often accompanied by anxiety, depressed mood, and avoidance behaviors. According to ICD-11 criteria, AjD symptoms emerge within three months of a stressor and typically resolve within six months after the stressor ends, although in many cases they can persist longer and contribute to chronic distress.

Epidemiological studies indicate that AjD is highly prevalent, affecting up to 30% of clinical populations and a substantial proportion of the general public during times of widespread stress. Despite this, AjD remains understudied compared to mood and anxiety disorders. Few empirically validated psychological interventions are available, and existing treatment recommendations are often extrapolated from evidence on depression and anxiety.

The COVID-19 pandemic presented a unique context in which AjD rates surged globally. Fear of infection, prolonged social isolation, economic uncertainty, and disruption of daily life contributed to high levels of stress-related distress. Surveys during the pandemic indicated that 18-43% of adults in Europe reported symptom patterns consistent with AjD, underscoring the urgent need for scalable interventions that could be delivered remotely and at low cost.

Mindfulness-Based Cognitive Therapy (MBCT) MBCT is an eight-week, group-based psychological program originally developed to prevent relapse in recurrent depression. It combines mindfulness meditation practices with cognitive-behavioral therapy strategies, fostering non-judgmental awareness of present-moment experience, greater cognitive flexibility, and reduced reactivity to negative thoughts and emotions.

Mechanistic research suggests that MBCT works by:

Increasing cognitive defusion - the ability to step back from and observe thoughts without automatically believing or reacting to them.

Reducing experiential avoidance - the tendency to suppress or avoid difficult emotions and sensations.

Enhancing self-compassion - a kinder, more understanding stance toward oneself in times of suffering.

These processes are relevant to AjD, where stressor-related rumination and self-critical coping often maintain distress. Although MBCT's efficacy for depression and anxiety is well-established, little is known about its effects in AjD or its feasibility in brief, fully online, self-guided formats.

Internet-Delivered MBCT (iMBCT) Internet-delivered psychological interventions (IPIs) have the potential to greatly expand access to evidence-based care. Online MBCT (iMBCT) can be delivered synchronously (live sessions with a facilitator) or asynchronously (self-paced, unguided), with evidence supporting effectiveness in reducing distress and improving resilience. Unguided iMBCT programs are especially promising for public health implementation due to their low delivery cost and scalability, but high-quality trials in specific clinical groups remain rare.

Study Objectives

The primary aim of this study was to evaluate the efficacy of a four-week, unguided, internet-delivered MBCT program for adults meeting ICD-11 criteria for AjD during the COVID-19 pandemic. We compared iMBCT with:

An active control - a four-week, unguided internet-delivered Progressive Muscle Relaxation (iPMR) program.

A passive control - a wait-list control (WLC).

Secondary aims were to examine whether changes in key psychological processes (cognitive fusion, experiential avoidance, self-compassion) mediated symptom improvement, providing insight into the mechanisms through which iMBCT exerts its effects.

Methods Overview This was a three-arm, parallel-group randomized controlled trial. A total of 301 adults from Poland who met ICD-11 AjD criteria (based on the Adjustment Disorder New Module - 20) were randomized to iMBCT, iPMR, or WLC. Interventions lasted four weeks, with assessments at baseline, post-intervention, and one-month follow-up (for intervention groups).

Interventions

iMBCT: A self-guided adaptation of MBCT condensed to six modules over 30 days. Modules included audio-guided mindfulness meditations (body scan, sitting meditation, mindful movement), reflective journaling, and psychoeducational materials. Content was delivered through a secure online platform with automated email reminders.

iPMR: A self-guided Progressive Muscle Relaxation program based on the Bernstein and Borkovec protocol, progressing from tensing and releasing 16 muscle groups to relaxation through mental recall. Audio instructions and written materials were provided.

WLC: No intervention during the 4-week study period. Participants were offered a choice of iMBCT or iPMR afterward.

Outcomes and Process Measures

Primary outcomes:

AjD symptoms (ADNM-20)

Depressive symptoms (PHQ-9)

Anxiety symptoms (GAD-7)

Process measures:

Cognitive Fusion (CFQ)

Experiential Avoidance (AAQ-II)

Self-Compassion (SCS-SF)

Key Findings

All groups showed significant symptom reductions over time, but iMBCT participants had greater improvements in depression and anxiety than both iPMR and WLC.

AjD remission rates were highest in the iMBCT group.

Cognitive defusion fully mediated the effect of iMBCT on depression and anxiety, suggesting it is a key mechanism of change.

Increases in self-compassion were observed only in the iMBCT group compared to WLC.

Benefits in the intervention groups were maintained at one-month follow-up.

Significance and Implications This trial provides the first randomized evidence that a brief, unguided iMBCT program can effectively reduce symptoms of AjD, depression, and anxiety, and improve transdiagnostic processes associated with resilience. Its low cost, scalability, and sustained benefits make it a promising tool for addressing stress-related disorders in situations where traditional face-to-face therapy is unavailable or impractical, such as during large-scale public health crises.

The findings also add to the mechanistic literature on MBCT, highlighting cognitive defusion as a central pathway to symptom improvement in AjD. This may inform refinements in mindfulness-based interventions and encourage further research on tailoring MBCT to specific stressor-related conditions.

Future research should test longer-term outcomes, evaluate implementation in diverse cultural contexts, and explore the integration of brief guidance or peer support to reduce attrition.

Inclusion Criteria:

Participants are required to be (a) at least 18 years old, (b) have access to the Internet, (c) currently experiencing some form of psychological distress related to COVID-19 pandemic, such as stress, anxiety, and/or low mood, and d) have the willingness to commit to a free online intervention program with two pre and post measurements online, within four weeks.

Exclusion Criteria:

(a) participating simultaneously in any pharmaceutical or psychosocial therapy, (b) if they were suffering from a current or lifetime psychotic disorder, bipolar disorder, or substance abuse problem; (c) if they reported current suicidal tendencies, (d) if they did not meet criteria for Adjustment Disorder (less than 47,5 points in ADNM-20 questionnaire), (e) participated in the past or currently in any of 8 weeks mindfulness programs (e.g., MBSR, MBCT).

At this time, it has not been determined whether individual participant data (IPD) will be shared. The decision will depend on considerations such as participant privacy, applicable legal and ethical requirements, and the availability of resources to prepare de-identified datasets.