The present study will use a randomized controlled design to investigate group differences between students with and without a history of nonsuicidal self-injury (NSSI) in response to a single-session mindfulness induction across conditions (formal mindfulness induction, informal mindfulness induction, active control task) in terms of the intervention's acceptability and effectiveness. Effectiveness will be inferred via pre-post changes in state mindfulness, state stress, and state well-being.

As university students have reported increasing levels of stress and difficulty coping with the challenges of university, student services have had to consider alternative approaches to meet the demand for student support. Thus, universities have moved beyond traditional mental health services to instructional, resilience-building approaches to enhance students' resilience and coping capacity. Mindfulness is a common foundation of these approaches due to the substantial evidence demonstrating the mental health and well-being benefits of mindfulness in university students. However, subgroups within the university student population may respond differently to standard mindfulness instruction.

Specifically, research suggests that university students who engage in non-suicidal self-injury (NSSI; the deliberate destruction of one's bodily tissue in the absence of lethal intent) may respond to mindfulness practice differently than students without such a history. Students with a history of NSSI are particularly prone to experiencing challenges in terms of stress, coping, and well-being in the university context. Thus, these students stand to benefit greatly from mindfulness-based programming that is adapted to their needs.

Standard mindfulness instruction generally consists of a combination of formal and informal practice. Formal practices can be conceptualized as structured, sustained attentional guided activities in which mindfulness is practiced within an allotted period of time (e.g., sitting meditation, body scan), whereas informal practices are brief and unstructured, and focus on the experience of one's senses during routine activities (e.g., becoming aware of the feeling of water on one's hands while washing them). Formal practice often requires sustained attention on one's inner experience (i.e., thoughts and emotions) and bodily sensations. Thus, existing difficulties with emotion regulation, self-criticism, and a potentially complex relationship with their body may render this common component of formal mindfulness practice sub-optimally effective among students with a history of NSSI.

By contrast, informal mindfulness strategies that are brief and unstructured may be more appropriate for these students. Nevertheless, only a few studies have attempted to parse out the benefits of formal and/or informal practice, and the results suggest benefits of informal mindfulness that are distinct from formal mindfulness. Furthermore, a recent systematic review examining the benefits of informal mindfulness concluded that informal practices may be more acceptable among those already experiencing difficulties with emotion regulation (e.g., those with recent NSSI engagement). The need for additional studies exploring the potentially differential acceptability and effectiveness of formal and informal mindfulness instruction among groups with unique intrapersonal needs was underscored.

Thus, the present study will use an online, parallel-group, randomized controlled design to investigate group differences between students with and without a history of NSSI in response to a single-session mindfulness induction across conditions (formal mindfulness induction, informal mindfulness induction, active control task) in terms of the intervention's acceptability and effectiveness. Effectiveness will be inferred via pre-post changes in state mindfulness, state stress, and state well-being.

Primary (state mindfulness) and secondary (state stress, state well-being, and acceptability) outcomes will be assessed immediately pre- and post-intervention. It is hypothesized that university students with a history of NSSI will report greater improvements in state mindfulness, state stress, and state well-being (Hypothesis 1a; superiority) as well as greater acceptability (Hypothesis 2a; superiority) in the IM condition, compared to those in the FM and control conditions. University students with a history of NSSI are also expected to report greater improvements in state mindfulness, state stress, and state well-being (Hypothesis 1b; superiority) as well as greater acceptability (Hypothesis 2b; superiority) in the FM condition, compared to those in control condition. Conversely, university students without a history of NSSI are expected to report noninferior improvements in state mindfulness, state stress, and state well-being (Hypothesis 1c; noninferiority) and noninferior acceptability (Hypothesis 2c; noninferiority) in the IM condition, compared to those in the FM. However, these students are expected to report greater improvements in state mindfulness, state stress, and state well-being (Hypothesis 1d; superiority) as well as greater acceptability (Hypothesis 2d; superiority) in the IM and FM conditions, compared to those in the control condition.

Inclusion Criteria:

• Current student at the host institution
• 18-29 years old
• Either a history of engaging in NSSI on at least 5 separate days in the last year or no history of ever having engaged in NSSI

Exclusion Criteria:

- Having a history of NSSI that does not fulfill the recency/frequency requirement