The aim of the present research is to explore whether a brief, smartphone app-based intervention based on psychological theory can help adolescents to avoid self-harming.

The smartphone app will be piloted in a randomised controlled trial (RCT) with adolescents. 90 adolescents will be recruited and assigned to one of three conditions: (a) intervention group who will complete the smartphone-based VHS app for self-harm (n = 30), (b) control group (n = 30) who will complete paper-and-pencil modified VHS, without the app, and (c) control group who will complete measures via the app but not the VHS (n = 30).

Background Self-harm among young people is frequent (McManus et al., 2019) and presents a growing public health concern in England. To date, no robust and comprehensive evidence base exists for effective interventions to prevent self-harm in adolescents (Witt et al., 2021). Therapeutic interventions that are effective among adults, including dialectical behavioural therapy, are only offered to CAMHS patients being diagnosed with a severe mental illness. Young patients with experiences of self-harm and their carers need to access interventions quickly to improve clinical care and reduce future harm. Therefore, novel interventions need to be developed, tested, and evaluated for this vulnerable population.

One such potential intervention is the "volitional help sheet" (VHS). The VHS is a brief psychosocial intervention that significantly reduces thoughts and acts of self-harm in adults admitted to hospital following an initial episode of self-harm (O'Connor et al., 2017). It is based on IF-THEN statements that help people link critical situations to alternative appropriate responses (Armitage, 2008; Gollwitzer, 1993). An example is: "If I feel the urge to self-harm when I want to get relief from a terrible state of mind, then I will do something else instead of self-harming". IF-THEN statements are intended to act as automatic coping responses, especially in cases where people may feel the urge to self-harm.

The VHS has previously been successful in reducing self-harm in people recently admitted to hospital for self-harm (Armitage et al., 2016; O'Connor et al., 2017). Recent data have also demonstrated that a web-based version of the VHS was acceptable among a large representative sample of UK adults with self-harm experiences (Keyworth et al., 2021). However, it is yet to be known whether this intervention is effective and acceptable among adolescents. It is important to conduct this research with experts by experience to create an acceptable and effective intervention, particularly since talking about self-harm does not increase risk of self-harm (Biddle et al., 2013; Blades et al., 2018), and can actually be positive experience for patients (Alexander et al., 2018; Dazzi et al., 2014). This research will co-adapt and pilot the VHS intervention in adolescents presented at CAMHS following an initial episode of self-harm. To maximise engagement with the intervention, we plan to develop this as a smartphone app.

Methods Design Pilot randomised controlled trial. Participants Adolescents who have previously harmed themselves. Setting Data collection will take place online. We will recruit both adolescents that are currently under the care of CAMHS, and those who have been discharged back to community care.

Recruitment and sampling A sample of 90 adolescents that have experienced and index episode of self-harm will be recruited through purposive sampling via Salford CAMHS and 42nd Street.

Materials A smartphone-based app version of the VHS will be developed. A pencil-and-paper modified VHS will be used for the active control group. A second version of the app will be developed to capture measures for the passive control group.

A novel questionnaire will be developed to run natively within the app to capture measures of effectiveness. Measures of current ideation and history of self-harm episodes alongside demographic information and potential mechanisms (e.g., capabilities, opportunities and motivations to avoid self-harm (Keyworth et al., 2020)) will be collected at baseline and at 6-months post-intervention.

Self-harm will be assessed with three items taken from the British Psychiatric Morbidity Survey (McManus et al., 2016) measuring non-suicidal self-harm (NSSH), suicidal ideation, and suicide attempts. Potential mechanisms will be captured using four measures: exposure to suicide and mental imagery about death; capabilities, opportunities and motivations; habits; and self-regulation. Questions based around the Theoretical Framework of Acceptability (Sekhon et al., 2017) will capture participant perceptions of the acceptability of the intervention. Uptake of the intervention will be measured at follow-up by measuring the frequencies with which critical situations were encountered and appropriate responses were used.

Procedure Data will be collected at two time points over a period of 6 months: baseline, and at six-month follow-up. Participants will be randomised into one of three conditions, to either receive the modified app-based VHS (intervention group; to make links between situations and solutions), a pencil-and-paper VHS (active control group; to make links between situations and solutions), or an app with no VHS component (passive control; where participants asked to identify situations and solutions, without making explicit links between them).

Participants will firstly be asked to complete a short series of demographic questions via an online questionnaire. This will be collected via an online survey which will be emailed to participants in the pencil-and-paper condition, and will be integrated into the app for conditions 1 and 3. Participants will also be asked about their history of self-harm, and questions to assess any psychological aspects involved in self-harm. To test the effectiveness of the intervention measures of non-suicidal self-harm (NSSH), suicidal ideation, and suicide attempts will be assessed via the app's questionnaire.

Participants in the two VHS conditions will be asked to construct "IF-THEN plans" which aim to support patients to reduce self-harm. After participants have created their "IF-THEN plans" they complete a series of questions about their experiences taking part in the intervention. These questions are to assess the feasibility and acceptability of "IF-THEN" plans in the context of self-harm and to iteratively modify the existing VHS. All questions will be optional and participants can choose to skip any should they desire.

Participants in the passive control condition will be asked to identify important situations and coping strategies that they can employ, but without making explicit links.

Ethical considerations Participants will be informed about the study before they agree to take part in it, they are under no obligation to participate in the study, and are free to withdraw from the study at any time, without giving a reason (this information will be in the participant information sheet).

People who self-harm are a vulnerable group who are likely to be experiencing emotional turmoil but they are an essential group to include in research, especially on self-harm services which are of variable quality. Participants may be become emotional when discussing experience with mental health services. However, evidence suggests that participating in research studies can be beneficial for vulnerable groups (Batterham et al., 2018; Blades et al., 2018), and that exposure to suicidal related content does not increase risk of suicidal ideation or engaging in suicidal behaviour (Alexander et al., 2018; Smith et al., 2010).

Our experience running a previous trial using a similar intervention confirms that adverse events are rare. However, there is a low risk of some participants finding the VHS difficult as it may induce uncomfortable emotions or result in distress. This is largely because it focuses on participants identifying situations where they may be tempted to self-harm.

Similarly, our experience running a previous trial using a similar intervention confirms that adverse events are rare, but discussions about inpatient discharge may induce distress.

All participants will be informed of the possible risk of distress in the Participant Information Sheet. Full contact details of the lead researchers will also be provided should participants wish to contact the research team to discuss any queries before they are asked to consent to take part. It will also be suggested to participants that if they feel that taking part in the study induces significant emotional distress or increases feelings related to self-harm, then they may need to reconsider their decision to partake.

All participants will be informed they do not need to answer any questions they do not wish to. They also will be free to withdraw from the study at any time without any penalties. Participants will be advised to withdraw from the study at any point should they become distressed (possibly stopping altogether or taking a break depending on how the participant wants to proceed). Where participants experience significant distress, they will be encouraged to speak with their GP about this at the earliest opportunity.

Participants will have a history of self-harm and it is possible that participants will engage in self-harm during or following the study. Therefore, there may be instances where confidentiality needs to be broken (e.g.: reports of self-harm). Participants will be made fully aware of the limits of confidentiality via the information sheet and consent form. A list of self-harm resources will also be provided as part of the participant Information Sheet.

Participants can opt out of the survey at any time if they are experiencing distress. A page with contact information for support services (e.g., NHS 111, MIND, the Samaritans, Saneline) will be included in the survey for any patients who may become distressed while discussing the subject matter in the online survey.

Researchers will have experience of working on sensitive topics and will meet regularly with the wider research team where any concerns can be reflected upon and discussed.

Inclusion Criteria:

• Adolescents aged between 12-18, who have been admitted to acute mental health in the past year or diagnosed with functional mental health problems

Exclusion Criteria:

• Individuals who cannot give informed consent, or whose parent/guardian cannot give informed consent.
• Individuals under the age of 12 years

The allocation sequence will be concealed from the researcher by using a centralised service (e.g., trial coordination centre) to ensure that selection remains unbiased. Thus, the trial will be double-blind.