This paper aims to understand how science and technology experts working in the digital mental health field interpret the ethical and social implications of its technologies, combining an ‘expert interview’ methodology with insights from sociotechnical systems theory. Following recruitment of experts in science and technology fields who had experience of supporting the development of DMH interventions, 11 semi-structured interviews were conducted and analyzed in accordance with the Framework Method. A single theme of ‘complexity of implications’ is presented here and divided into the categories of ‘implications for users’, ‘implications for healthcare professionals and systems’, and ‘implications for society’. Participants identified a range of ethical and social implications of digital mental health technologies at the three different levels, which this discussion relates to three key aspects of complex sociotechnical systems identified in existing theoretical work. These are ‘heterogeneity’, ‘interdependence’ and ‘distribution’, each of which raises important questions for future research about how complex values, relationships and responsibilities should be negotiated in digital mental health. The paper concludes that this study’s approach provides a model for understanding the implications of digital health more broadly, with participants’ combined experience and knowledge shedding light on key interventions at the forefront of digitalization in healthcare.