(Salomon et al., 2012, 2015). This implies that ultimately the program cost USD PPP (2019) 18,413 per DALY averted. Since Uganda had a GDP per capita USD PPP (2019) of 2,345, the IPT-G intervention cannot be considered cost-effective using this benchmark.

Given significant and large short-term effects found in a previous study of IPT-G in Uganda which examined the use of IPT-G to treat depression in adults with trained lay facilitators (Bolton et al., 2003),<sup>24</sup> it is worth exploring possible explanations for both the smaller than expected short-term impacts of IPT-G on mental health, and lack of longer-term effects found in this study. First, and most obvious, is the timing of the intervention in relation to the COVID-19 pandemic, with therapy finishing in late 2019, a few months before the onset of the pandemic. The pandemic was a large and unprecedented global negative shock that may have simply been too catastrophic for group therapy to overcome. Second, there was – a high rate of recovery in the control group approximately a quarter of the adolescents in the control group did not suffer from depression or psychological distress at 24-months, a finding also noted in other studies of adults (e.g., Baranov et al. (2020), Bhat et al. (2022), and Bolton et al. (2003)). This finding points to a critical role for improved targeting of mental health interventions: further research is needed to understand how screening through a traditional tool like the PHQ-8 could be improved through a combination of other methods - such as better locally-adapted screening tools (Carvajal-Velez et al., 2023), children’s drawings (Baird et al., 2022), and risk prediction models (Rocha et al., 2021; Brathwaite et al., 2021). Finally, this evaluation was of a first attempt by StrongMinds to provide IPT-G to adolescents and to work through partner organizations. Lessons learned from this study combined with broader internal monitoring and evaluation led them to substantially alter their approach for treating adolescents at scale (StrongMinds, 2023b). This includes treating in-school and out-of-school adolescents separately, using teachers instead of peer-age mentors to lead IPT-G sessions, and more intensive training. Further research is needed to assess the impact of this revised model.

Overall, this paper highlights the challenge of tackling mental health at scale, particularly for adolescents in LMICs. While we continue to find evidence that adolescent programming — — both mental health specific and otherwise can improve mental health in the short

> 24IPT-G has been tested using RCTs in Uganda more than 20 years ago with very promising short-term results. Bolton et al. (2003) found large reductions in depression and dysfunction among adults in rural Uganda **two weeks** after the completion of IPT-G. However, in addition to the two decades that have passed since that intervention, there are important differences between their study and ours in _target population_ (adult males and females in rural Uganda vs. adolescent females); _targeting_ (using a locally adapted Hopkins symptom checklist among the subset of adults in study clusters who were believed to have depression-like illness vs. using PHQ-8 to screen in all adolescent females in the study areas); _follow-up duration_ (Bolton et al. (2003) do not report longer-term effects); and _take-up of IPT-G_ (54% of the participants attending at least 14 of the 16 sessions in the Bolton et al. (2003) study compared with 28% attending 12 of the 14 sessions in this study).

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