Previous research demonstrates that biomedicalisation and diagnostic processes are intertwined in American mental health care, but few studies examine practitioners’ negotiations. This study examines how Mental Health Practitioners (MHPs) negotiate the Diagnostic and Statistical Manual (DSM), diagnosis, standardisation and biomedicalisation‐in‐practice. Feminist grounded theory analysis of 42 semi‐structured interviews with licensed adolescent MHPs reveals accounts of discursive, everyday resistance to the DSM technology and standardisation, which I regard as key aspects of biomedicalisation. Findings demonstrate MHPs seemingly practice what I term diagnostic dissonance: a deep conflict between their professional theoretical orientations and the biomedical model legitimated in the DSM technology and insurers’ diagnostic standardisation. MHPs enact dissonance by undermining the DSM, working around standardisation and by coding the social. Coding the social refers to the employment of V‐codes – illegitimate secondary diagnoses – which convey social and relational conditions of mental distress. MHPs’ contestations of the DSM and standardisation are responses to a healthcare infrastructure that decontextualises mental health. Practitioner resistance to biomedicalisation‐in‐diagnosis is important because the biomedicalisation of mental health takes focus away from the social and relational conditions and solutions to individual and community health and illness.