This pilot RCT will test the preliminary efficacy of an intensive group model of Internal Family Systems (IFS) called the Program for Alleviating and Resolving Trauma and Stress (PARTS) compared with a Nature-Based Stress Reduction for Trauma Survivors (NBSR-T) attention placebo control group at reducing PTSD symptom severity measured by Clinician-Administered PTSD Scale (CAPS-5). In addition, the effects of the interventions on self-reported PTSD symptoms, disassociation, and disturbances of self-organization (DSO), as well as mechanisms of emotion regulation, decentering and self-compassion will be secondary outcomes.

The investigators will conduct a pilot RCT to test the preliminary efficacy of the Program for Alleviating and Resolving Trauma and Stress (PARTS) compared with a Nature-Based Stress Reduction for Trauma Survivors (NBSR-T) control group at reducing PTSD symptom severity measured by Clinician-Administered PTSD Scale (CAPS-5).

Secondary clinical outcomes include the effects of the intervention on self-reported PTSD symptoms (PCL-5; CAT-PTSD), disassociation (MDI), and disturbances of self-organization (ITQ). Secondary mechanistic outcomes include emotion regulation (DERS), self-compassion (SCS-SF), and decentering (EQ-D) .

Exploratory aims of the study are to investigate the effects on depression (CAT-DI), mental health (CAT-MH scales), self-trauma fusion (PRISM-D), perceived stress (PSS), internalized stigma (ISMI), and interoception (MAIA-2). Additional exploratory outcomes include changes in outcome variables among PTSD subjects with baseline DSO and those without DSO as defined by the International Trauma Questionnaire (ITQ).

Inclusion Criteria:

• Be able to bill insurance for individual psychotherapy at CHA;
• Be a current patient of CHA primary care, behavioral health care or CHA MINDWell;
• Have a current diagnosis of PTSD OR a CAT-MH PTSD score >58;
• Have sufficient English fluency and literacy skills to understand the consent process, procedures and questionnaires and have the ability to provide written informed consent;
• Have access to the internet and an electronic device with adequate data capacity; to complete questionnaires online and attend online videoconference groups;
• Must be available and willing to attend the scheduled online group sessions for 16 weeks; and must be available and willing to complete the online computerized assessments and phone interviews.

Exclusion Criteria:

• Inability to complete an informed consent assessment AND/OR inability to complete baseline study assessment procedures (due to cognitive deficit, non-proficiency in English literacy, or any other reason);
• Current participation in another experimental research study;
• Expected medical hospitalization in six months from the date of enrollment;
• Expected incarceration in six months from the date of enrollment;
• Individuals who are pregnant with a due date within 26 weeks after study consent;
• Insufficient level of severity of PTSD symptoms: CAPS-5 SEV2 Total score less than 26; PTSD score of less than 31 on the PTSD Checklist for DSM-V (PCL-5)8 at screening visit;
• Inability to participate safely in the study intervention and without disrupting the group (in the opinion of principal investigator OR meeting any of the following criteria):
• Past year history of a psychotic disorder or clinician confirmed active psychosis (Severe level of psychosis on PSY-S-CAT > 30 will trigger the requirement of a clinical assessment prior to participation in the program)
• Bipolar I disorder history or severe level of mania on CAT-MH5 (>70)
• Acute suicidality or self-injurious behavior
• Severe depression, indicated by CAT-DI > 755,65
• Acute homicidality with plan and/or intent;
• Hospitalization for suicide attempt or self-harm within three months of the enrollment period;
• Severe Borderline Personality Disorder or other severe personality disorder that may lead to disruptions within the group; and/or
• Moderate or severe Substance Use Disorder. In addition, use of or positive toxicology for illicit drugs (e.g., cocaine, opioids, etc.) or non-prescribed controlled medications (i.e., opioids, stimulants, or benzodiazepines) in the past 3 months.

Participants will be unaware of study hypotheses or arms and will be told the study is for stress reduction among people with trauma/PTSD.

The staff member responsible for final determination of study eligibility will be blinded to the randomization sequence.

The Data Analyst and methodologist will be blinded to participant identity prior to and during randomization and analysis.

The PI will be blinded to participant randomization status for the duration of the study.

Medical Review Officer: The MRO will not be blinded and will be responsible for advising on adverse events.

Independent Evaluators conducting the CAPS-5 assessments will be blinded to the participants' randomization status. To protect this, independent CAPS-5 evaluators will be located separately from group leaders and therapists. In the event of an unintentional unblinding, a new rater will be assigned to assess the relevant participant(s).