Anorexia nervosa (AN) has the highest mortality rate of any mental illness, with a typical onset in adolescence. Although family-based interventions are efficacious for up to 75 percent of adolescents with AN, approximately 30 percent will relapse after recovery. There is a critical need to improve treatments and prevent post-discharge relapse following acute treatment to improve outcomes for adolescents with AN.

To address this critical need, the investigators developed an adaptive smart-phone based therapy support tool for teens with AN, called Smart Treatment for Anorexia Recovery (STAR). STAR is for adolescents between the ages of 13-21 who recently received acute treatment for AN (e.g., inpatient, residential, intensive outpatient, or day hospital) who are currently working with an outpatient therapist. STAR incorporates elements from the Unified Protocol and Acceptance and Commitment Therapy to target emotion avoidance, which the investigators hypothesize will lead to reductions in eating-disorder behaviors. The investigators will compare STAR to Present-focused Anorexia Nervosa Coping Treatment (PACT), which focuses on current life stressors and problems.

The investigators' hypothesis is that STAR will improve outpatient treatment response and reduce relapse in adolescents discharged from intensive treatment for AN. The investigators will evaluate their hypotheses in two conditions: 1) STAR app and 2) PACT app. In both conditions, participants must be working with an individual outpatient therapist.

AN is the third leading cause of chronic illness in adolescents and, if left untreated, can lead to major organ damage, structural and functional brain changes, and early-onset osteopenia and osteoporosis. Although family-based interventions are efficacious for up to 75% of adolescents with AN, approximately 30% will relapse after recovery. There is a critical need to optimize treatments and prevent post-discharge relapse following acute treatment to improve outcomes for adolescents with AN. To address this critical need, the investigative team developed a suite of digital tools that advance the science of assessment, risk prediction, and clinical-decision support for use in the post-acute treatment window, called "Smart Treatment for Anorexia Recovery (STAR)." STAR uses cutting-edge assessment technology to shorten test administration and machine-learning to predict likelihood of recovery. This information is then provided back to the clinician via an easy-to-use clinical-decision support tool to alert the clinician when user-entered data suggests the patient is not progressing.

In the current clinical trial, the investigators will expand STAR to test an adaptive mHealth intervention delivered in the post-discharge window. The investigators' hypothesis is that a transdiagnostic assessment and clinical-decision support tool delivered within the STAR suite will optimize face-to-face clinical service and the addition of an adaptive mobile-health (mHealth) intervention will improve outpatient treatment response and reduce relapse in adolescents discharged from intensive treatment for AN. The investigators' previous work supports the hypothesis. Specifically, the investigators' past studies provide robust support for the predictive validity and clinical utility of the investigators' assessment tool for predicting ED-related psychiatric impairment and recovery. However, the number of items across the paper-based assessment tool is 144, which is overly long for routine use. To overcome this challenge, the investigators developed a mobile phone app that uses computerized adaptive testing to reduce assessment length by up to 50% while retaining the reliability and validity of the original paper-and-pencil measure. The investigators propose to leverage this innovation to optimize both face-to-face and mHealth treatment for AN. The objectives are to: 1) develop the mHealth intervention (with clinician and stakeholder input) and 2) establish feasibility, acceptability, and preliminary effect size of the mHealth intervention using both clinician and patient data. To accomplish these objectives, the investigators will employ a computerized adaptive test coupled with machine learning algorithms, delivered within the app to signal clinicians when their clients are at-risk for poor outcomes and relapse. Specific aims include: 1) adapt the existing clinical tool to provide therapist support modules and patient mHealth messages; 2) conduct a preliminary randomized controlled trial (RCT) of the integrated assessment and mHealth intervention tool; 3) test preliminary mechanisms that lead to changes in AN symptoms.

STAR incorporates elements from the Unified Protocol and Acceptance and Commitment Therapy to target emotion avoidance, which the investigators hypothesize will lead to reductions in eating-disorder behaviors. The investigators will compare STAR to Present-focused Anorexia Nervosa Coping Treatment (PACT), which focuses on current life stressors and problems. The investigators' hypothesis is that STAR will improve outpatient treatment response and reduce relapse in adolescents discharged from intensive treatment for AN. The investigators will evaluate hypotheses in two conditions: 1) STAR app and 2) PACT app. In both conditions, participants must be working with an individual outpatient therapist.

Given there is a scarcity of specialty care for AN following acute treatment, yet 95% of adolescents have smartphones, the proposed research is innovative and significant because it has the future potential to reduce relapse and optimize existing community-delivered interventions for AN over the post-acute treatment window.

Inclusion Criteria:

• Age 13 to 21
• Able to read and speak fluent English
• Access to a smartphone
• Received acute treatment for anorexia nervosa or atypical anorexia nervosa [residential, inpatient, partial hospitalization (PHP), or intensive outpatient program (IOP)] within the past three months
• Currently receiving weekly outpatient treatment (or planning to start outpatient treatment) for current anorexia nervosa/atypical anorexia nervosa, or past anorexia nervosa/atypical anorexia nervosa (e.g., anorexia nervosa in partial remission).

Exclusion Criteria:

• Uncorrected visual impairments that would prevent smartphone use
• Intellectual or developmental disability
• Medical condition that affects appetite or weight (e.g., thyroid disorder, diabetes, cancer, pregnancy)
• Current psychotic disorder or substance use disorder
• BMI-z < 14 or lab abnormalities indicating medical instability
• Unwillingness for data to be shared with outpatient therapist

De-identified data collected from this study will be made publicly available. The investigators will restrict any data that may reveal subjects' identities (e.g., geographical location). To protect subjects' privacy, publicly-available data will not contain any personally identifying or private health information (PHI). Consent forms will describe the data sharing plan so that participants are informed of how their data will be handled. Prior to the release of data, the investigators will require that a local privacy officer certify that all datasets contain no PHI. The investigators will also require that individuals requesting data sign a Letter of Agreement.

Data will be released in a timely fashion in waves as soon as the main study findings are published. Data will remain available in perpetuity.

Investigators interested in using the data will be required to contact the PI to provide a brief description of the intended use. Although investigators will be able to design and analyze the data as they choose, such documentation will prevent duplication of research and provide a greater level of protection of intellectual property. These instructions will be included in a peer-reviewed publication that describes the study design.