This study will evaluate the feasibility, acceptability, and preliminary effectiveness of a behavioral activation intervention designed for adults hospitalized on an inpatient psychiatric unit. The intervention includes two connected components: (1) a brief inpatient behavioral activation group delivered during hospitalization by unit staff (which is delivered to everyone as part of standard clinical care and not considered part of the study) and (2) a smartphone application that supports behavioral activation skills practice during the first 28 days after discharge.

Behavioral activation is a psychological treatment that aims to increase engagement in meaningful and rewarding activities and reduce patterns of avoidance that can worsen mental health symptoms. The intervention was designed specifically for the short length of stay and group-based structure typical of psychiatric inpatient care in the United States.

Participants will be recruited from an adult inpatient psychiatric unit at Rutgers University Behavioral Health Care.

The study uses an open trial design where there is no control group. Participants in the intervention condition will receive the behavioral activation group plus access to the smartphone application after discharge.

Participants will complete self-report assessments during hospitalization and throughout a 6-month follow-up period. During the first 28 days after discharge, participants will also complete smartphone-based ecological momentary assessments multiple times per day. Outcomes include depression, anxiety, suicidal thoughts and behaviors, functioning, behavioral activation, emergency department visits, psychiatric readmission, outpatient treatment engagement, and intervention feasibility and acceptability.

The current study is a hybrid type I implementation-effectiveness trial evaluating a multimodal behavioral activation intervention for adults receiving inpatient psychiatric treatment. The intervention was developed to address two major gaps in acute psychiatric care in the United States: limited access to evidence-based psychotherapy during hospitalization and limited support during the transition from inpatient to outpatient care. The intervention combines a brief inpatient behavioral activation group delivered by unit staff as part of standard care during hospitalization, supplemented with a smartphone-based digital intervention designed to support behavioral activation skills practice during the first 28 days after discharge.

Behavioral activation is an evidence-based psychological treatment that seeks to increase engagement in adaptive and rewarding activities while reducing patterns of avoidance associated with emotional distress and psychiatric symptoms. The intervention was specifically adapted for the structure of contemporary inpatient psychiatric care in the United States, including short lengths of stay, high patient turnover, and reliance on group-based treatment delivered by multidisciplinary staff with varying levels of formal psychotherapy training. The intervention was also designed to be transdiagnostic and appropriate for patients with a range of psychiatric disorders commonly treated in inpatient settings.

The inpatient component is flexible but generally consists of four stand-alone behavioral activation group sessions focused on activity planning, values identification, problem-solving, and reducing avoidance behaviors. Sessions are designed so that patients may benefit regardless of admission timing or number of sessions attended. Following discharge, participants will use a smartphone application that includes ecological momentary assessment prompts, behavioral activation skill reminders, activity planning tools, activity monitoring, and access to psychoeducational materials consistent with the inpatient group content. The application is intended to support behavioral activation skill implementation during participants' transition back into their daily environments

Inclusion Criteria:

• adult status (18+ years)
• admission to a hospital-based psychiatric inpatient service
• the ability to speak and write English fluently,
• ownership of and consistent access to an internet-capable smartphone (e.g., an iPhone or Android phone).

Exclusion Criteria:

• the presence of any factor that impairs an individual's ability to provide informed consent and comprehend and effectively participate in the study, including:
• an inability to speak or write English fluently
• the presence of gross cognitive impairment due to florid psychosis, intellectual disability, dementia, acute intoxication, or the presence of extremely agitated or violent behavior.

Data are from a sensitive population.