This study is the first to use population-level, nationally representative data to estimate the prevalence and disparities in mental ill-health, substance use and their co-occurrence, among sexuality diverse adolescents in Australia. This study is also the first to show preliminary evidence regarding the preventive utility of school climate and teacher self-efficacy for preventing and reducing mental ill-health and co-occurring substance use.

Our analyses identified alarming disparities in mental ill-health experiences by sexuality diverse adolescents, particularly sexuality diverse female adolescents. This provides further evidence that mental ill-health disparities are emergent during early adolescence, an important distinction from past research, which considers mental ill-health disparities among sexuality diverse young people broadly through adolescence and young adulthood (Gilbey et al., 2020; Hill et al., 2021b). These findings extend existing literature, which largely focuses on sex-differences in mental health among the general adolescent population (Campbell et al., 2021), or sexuality diverse adults (MacCarthy et al., 2021).

Sexuality diverse females were significantly more likely to use cannabis compared to heterosexual females, providing new evidence that previously identified disparities in cannabis use documented among sexuality diverse adult populations (Schofield et al., 2023) may, in fact, emerge before or during early adolescence. Urgent research coupled with education about the potential harms of cannabis use during adolescence is required to better understand and prevent cannabis use among sexuality diverse adolescents, given cannabis use is a significant risk factor for cannabis use disorder and associated psychiatric comorbidity (Teesson et al., 2012). Better understanding the impact of effective substance use prevention programmes that go beyond education provision is one possible pathway towards addressing this gap (Andrews et al., 2023; Thornton et al., 2018). It is hypothesised that cannabis use may be a coping mechanism for minority stress, that is, how heterosexist society privileges heterosexual people to stigma, discrimination and subsequent mental ill-health detriment of sexuality diverse people (Buttazzoni et al., 2021; Meyer, 2003). Additional public health efforts are required to address the complex pathways between minority stress and cannabis use among sexuality diverse adolescents with the view to preventing and reducing cannabis use as a potentially harmful coping mechanism (Buttazzoni et al., 2021; Schofield et al., 2023). Furthermore, due to relatively low response rates to substance use items, albeit largely system missing, future research on substance use disparities among sexuality diverse adolescents would benefit from leveraging large sample sizes to improve confidence and precision in estimates.

Our study illustrates the disproportionate burden of co-occurring mental ill-health and substance use affecting sexuality diverse adolescents, particularly the potential use of multiple different substances in co-occurrence with high levels of emotional symptoms and self-harm thoughts/behaviour. These findings represent a significant and novel contribution to the literature given most previous research is largely limited to sexuality diverse adults (Felner et al., 2021; Han et al., 2020) or individual mental ill-health and/or substance use as siloed public health issues (Scheer et al., 2022; Watson et al., 2020). While part of our findings may be explained as sexuality diverse adolescents using substances to cope with sexuality diversity-related minority stress and associated and/or independent symptoms of depression and anxiety (Felner et al., 2020; Johannessen et al., 2017), co-occurring substance use and self-harm thoughts/behaviours pose a slightly more complicated public health issue. Self-harm is commonly documented in the literature as being a coping mechanism in and of itself, for mental ill-health and life adversity (Guerreiro et al., 2015; Klineberg et al., 2013). Moreover, self-harm thoughts/behaviours during adolescence are strong predictors of substance use and misuse through adolescence and adulthood (Moran et al., 2015). Further research and tailored community-engaged public health support is required to better understand experiences of sexuality diverse adolescents coping with mental ill-health, particularly those with self-harm thoughts/behaviours and/or substance use. Without further preventive research and intervention, co-occurring mental ill-health and substance use among sexuality diverse adolescents, particularly that involving self-harm thoughts/behaviours, renders this population at significantly higher risk of chronic, debilitating substance use disorders and significant psychiatric morbidity across the lifespan.

Importantly, positive school climate appears to buffer and reduce mental ill-health among sexuality diverse adolescents within this sample, in the early to middle stages of their schooling experiences. This highlights a highly feasible way to improve efforts to support sexuality diverse young people within the school environment. Past research often defines school climate with respect to sexuality diverse young people as the presence or absence of sexuality diverse-specific programmes or policies, such as GSAs or anti-bullying policies, yet these measures fail to capture the totality of school as a physical and cultural institution that deeply influences how students perceived themselves and their relationships with peers and staff (Colvin et al., 2019; Day et al., 2020; Leung et al., 2022; Parodi et al., 2022). Hence, our findings provide robust evidence for the necessity and public health preventive value of whole-of-school approaches that are affirming, inclusive and supportive of sexuality diverse young people, especially those in early adolescence, to combat already emergent and pronounced mental ill-health disparities. These school-wide approaches are defined as predictable, reliable routines conducive of affirming and including sexuality diverse adolescents, including the provision of information and support relating to sexuality diversity to all students, school-wide teacher professional development and inclusive curricula (Russell et al., 2021).

Our study also provides preliminary evidence that teacher self-efficacy indeed plays a significant role in sexuality diverse mental ill-health, specifically during early adolescence. Sexuality diverse adolescents are at significantly increased risk of bullying and harassment compared to their heterosexual peers (Ullman, 2021). Further research is required to understand whether teacher self-efficacy is associated with positive adult intervention in these adverse experiences. Notwithstanding this, these findings point to an important evidence-based policy recommendation that teachers and other school practitioners should undergo formal training and professional development tailored specifically to affirming, supporting and including sexuality diverse adolescents. Current Australia-specific findings suggest gender and sexuality diversity is the subject teachers and other school staff feel least comfortable teaching and discussing with students (Ezer et al., 2021). Within the wider school climate, teachers specifically play an important role in preventing and reducing mental ill-health among sexuality diverse adolescents and young people. Additional research should also identify whether teacher self-efficacy is associated with mental ill-health among trans, non-binary and gender-diverse young people (those adolescents with a gender identity different to the gender presumed for them at birth, henceforth respectfully referred to using the umbrella term, ‘trans’) given their relatively higher burden of mental ill-health. It is also important to note that the teacher self-efficacy and school climate measures were not specific to sexuality diversity nor were the religion of participants or their respective schools examined. Hence all schools including government, private and religious schools should be looking to promote teacher self-efficacy in managing behavioural and learning problems and improving school climate to ensure all young people feel they can be themselves at school.

Whereas our study benefitted from significant strengths such as a large, nationally representative, cohort of sexuality diverse adolescents, a comprehensive assessment of mental ill-health symptomatology and recent substance use, and the use of both student- and teacher-report measures, this study is not without limitations. Missing data on substance use and teacher self-efficacy, albeit largely system missing in nature, may have biased the external validity of the sample, particularly if teacher non-respondents were less likely to possess self-efficacy about their teaching abilities. Future research drawing on both student- and teacher-reports of mental health and school climate should capture comprehensive demographic and psycho-social influences for both the adolescent participant but also their teacher, to ensure any missing data can be subject to rigorous sensitivity analyses. While the school climate measure utilised in this study is highly reliable and valid, its focus is on the adolescent’s perceived sense of belonging within school, which does not incorporate other facets of school climate, including safety/discipline, equality of opportunity and environment (Gonzálvez et al., 2023). Moreover, the PSSM scale does not include specific items relating to the level of sexuality diversity affirmative and inclusive measures in schools, a likely important factor imperative for contemporary studies of school climate and especially sexuality diverse adolescent’s perceptions of school climate. Future research should draw on sexuality diverse specific measures of school climate, such as the recently validated Gender Climate scale (Ullman et al., 2023), to strategically determine which aspects of school climate can best be modified to promote mental health among sexuality diverse adolescents. Due to limited sample size, analyses of school climate and teacher self-efficacy associations with co-occurring mental ill-health and substance use outcomes should be interpreted with caution. Furthermore, this limitation may also explain the unexpected finding of an association between past 12-month cannabis use and improved teacher self-efficacy, and any mental ill-health and past 12-month cannabis use and improved teacher self-efficacy. Further research harnessing large sample sizes of sexuality-diverse adolescents and their heterosexual peers are required to establish the true effect estimate of the relationship between school climate, teacher self-efficacy and mental ill-health and substance use outcomes. The four bespoke items assessing teacher self-efficacy were also a limited qualification of teachers’ true sense of efficacy despite generating an acceptable level alpha co-efficient. Moreover, it was unclear whether some participants shared teachers. While analyses adjusted for geographical postcode-level clustering, there may have been residual confounding if there was a potential lack of independence of observations. Future relevant research should incorporate teachers’ personal values and motivations for teaching (Barni et al., 2019), particularly in relation to sexuality diversity and inclusive education, to understand how these can be modified for the benefit of adolescent mental health. Another limitation of the study relates to how this wave of the LSAC study did not include gender indicators, preventing any analyses on trans, non-binary and gender diverse adolescents. Trans adolescents experience vastly greater mental ill-health disparities compared with their cisgender peers. Rates of mental ill-health among trans adolescents are typically observed as higher than those among sexuality diverse adolescents. Future research leveraging nationally representative, population-level sampling methodologies should ensure that adequate gender indicators are included to enable high-quality public health research to promote trans mental health.

In summation, mental ill-health and substance use, and especially their co-occurrence, are highly prevalent among sexuality diverse adolescents in Australia and pose significant and inequitable risks to health and well-being through adolescence and across the lifespan. Urgent research and community-sensitive preventive education is required to address this critical public health issue. Schools represent a potential site for focusing these prevention efforts. Educating and training teachers is a promising pathway towards optimising school-based prevention.