Suicidal thoughts, suicide attempts, and suicide are increasingly common in adolescence.

Current face-to-face prevention approaches are of limited effectiveness, rely on extensive resources, and are at odds with adolescents' digital preferences. We will evaluate two unconventional but promising interventions delivered to 13- to 17-year-olds: transcutaneous vagus nerve stimulation to target emotion dysregulation, and a peer-support smartphone app to combat social isolation. If effective, these digitally-delivered interventions could reach far more adolescents at far lower cost than current approaches.

Over the past two decades, suicide rates have increased nearly 35% in the U.S., with upward trends in nearly all demographic groups. Further increases have occurred since the COVID-19 pandemic began. Despite ambitious goals for reducing suicides and significant federal and private investment, suicide rates continue to rise unabated. To date, the predominant approach to mitigating suicide risk in the U.S. is secondary prevention. Typically, these programs identify risk of recurrence among those who have already attempted suicide at least once. Although secondary prevention is crucial, the majority of deaths by suicide occur on first attempt. Thus, targeted primary prevention earlier in development is essential. Most current primary prevention programs are intensive, expensive, and delivered by highly trained mental health providers, who are in short supply. Traditional face-to-face therapy is also unavailable to many who live in underserved communities, and disliked by adolescents, who much prefer digital delivery on their devices. This high-risk, high-reward proposal addresses these limitations and needs. We use an experimental therapeutics approach to evaluate the independent and combined efficacies of two unconventional but scalable interventions: transcutaneous vagus nerve stimulation (tVNS) to target emotion dysregulation, and a peer-support smartphone app to combat social isolation. These low-cost interventions, which hold strong promise but have not been used before, can reach large numbers of adolescents, with much potential to reduce prospective suicide risk. We will enroll 212 adolescents, ages 13-17 years, who show elevations on at least two prominent risk factors for suicide (e.g., self-injury, maltreatment).

Using a 2 × 2 design, adolescents will be assigned randomly to receive 30 days of treatment with:

1. tVNS to target emotion dysregulation,
2. a peer-support phone app to target social isolation,
3. tVNS + a peer-support phone app, or
4. enhanced treatment as usual with monitoring and access to resources.

Intervention effects on mechanisms (emotion dysregulation, social isolation) proximal efficacy signals (e.g., physiological reactivity, self-harm) and target outcomes (suicidal ideation, suicidal behaviors) will be evaluated immediately post-intervention and at one-year follow-up. Treatment data will be monitored daily to fine-tune dosing of both interventions. This transformative and innovative proposal tests two novel, scalable preventive interventions designed to "meet adolescents where they are" by using digital technologies to address core mechanisms of suicide risk.

Inclusion Criteria:

• Aged between 13 and 17 years,
• Daily access to a smartphone
• Attend in person meetings in South Bend, IN or Rochester, NY. and,

Two of the following which will be scored during the phone screen:

• High scores on social isolation
• High scores on emotion dysregulation
• Has engaged in NSSI (inclusive of a single act)
• High T-scores on impulsivity,
• High T-scores on depression
• Engages in alcohol or other substance use

Exclusion Criteria:

• Parent reported autism or schizophrenia
• Implanted pacemaker or cardiac defibrillator, other implanted or metallic device
• Pregnant or breast feeding
• History of seizures or epilepsy
• TMJ Disorder
• Bells' Palsy
• Impaired cranial nerve function
• Facial Pain

There is no plan to share individual participant data outside of the study team.