The goal of this clinical trial is to learn whether a combination of brief digital and clinician-delivered interventions can help adults leaving a psychiatric hospitalization cope with suicidal thoughts and prevent suicide-related events.

The main questions it aims to answer are:

• Are people who receive automated smartphone messages when they report suicidal thoughts after leaving the hospital less likely to have a suicide-related event than those who do smartphone self-monitoring alone?
• Are people who have additional session(s) with a clinician in the four weeks after leaving the hospital less likely to have a suicide-related event than those who receive additional brief self-guided intervention(s)?

Participants will be asked to:

• Make a personalized safety plan (of coping strategies to use when feeling suicidal) before leaving the hospital
• Do self-monitoring of suicidal thoughts and related experiences on their smartphone for four weeks after leaving the hospital
• Complete a longer set of research questionnaires at the start of the study and five more times during the 12 weeks after leaving the hospital

Depending on which study group they are in and whether they benefit from initial smartphone interventions, participants may or may not:

• Receive automated smartphone messages reminding them of coping strategies to use for suicidal thoughts
• Receive up to three additional sessions with a study clinician
• Receive up to three brief online self-guided interventions

The study interventions last for the four weeks after leaving the hospital. Participants will also be asked permission to share information from their health records about care received for 12 weeks after leaving the hospital.

Over 49,000 Americans die by suicide each year, making suicide the 11th leading cause of death across all ages. The highest-risk time for suicidal behavior is the three months after inpatient psychiatric hospitalization, during which engagement with traditional outpatient care is low. Recent real-time monitoring research has revealed that suicidal thoughts fluctuate rapidly, over hours or even minutes, highlighting the need for dynamic interventions that adapt to time-varying changes in risk. Just-in-time adaptive interventions (JITAIs) can help promote timely coping strategy use during periods of elevated suicidal thinking. Some people, however, will require additional interventions that explicitly target common barriers to coping effectively with suicidal thoughts. Evidence-based single-session interventions (SSIs) that address coping with suicidal thoughts exist and can be delivered in either clinician-delivered or self-guided formats. This study will use a hybrid experimental design that leverages both Sequential Multiple Assignment Randomized Trial and Micro-Randomized Trial (MRT) methods to build and evaluate a multimodality adaptive intervention comprising stepped evidence-based intervention components sequenced and adapted at multiple timescales following inpatient hospitalization.

Aim 1 will compare two first-stage interventions: JITAI vs. self-monitoring alone for four weeks after inpatient discharge. The investigators will determine the effectiveness of the JITAI for reducing the risk of suicide-related events (SREs) over three months and whether the JITAI engages target mechanisms related to coping.

Aim 2 will compare two second-stage interventions for those who do not sufficiently respond to the first-stage interventions: clinician-delivered or self-guided SSIs targeting individualized barriers to coping strategy use. Response status will be assessed weekly for four weeks post-hospitalization. The investigators will determine the effectiveness of clinician-delivered vs. self-guided SSIs for reducing the risk of SREs among insufficient responders, as well as effect differences between embedded adaptive interventions among all participants.

Aim 3 will determine the within-person effects of just-in-time messages on proximal outcomes (next-hour coping strategy use and momentary suicidal thoughts) for participants in the JITAI condition. Just-in-time message effects will be evaluated when averaging across second-stage conditions and contrasting message and SSI types.

This study will result in a scalable and optimized stepped approach to reducing suicide risk during a key care transition period.

Inclusion Criteria:

• Adult status (18+ years-old)
• Ownership of a smartphone (iOS or Android)
• Inpatient admission due to suicidal thoughts or suicide attempt

Exclusion Criteria:

- Presence of any factor that impairs an individual's ability to 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

In accordance with NIH guidelines, individual participant data collected in this study (including self-report and demographic data), as well as a corresponding data dictionary, will be shared via the National Institute of Mental Health National Data Archive (NDA).