BackgroundPsychiatric nurses are in a unique position to build therapeutic relationships with mental healthcare users with dual diagnoses to foster trust and recovery. However, a dual diagnosis poses barriers to establishing and maintaining a therapeutic nurse–patient relationship.AimThe overall aim of this study was to explore and describe barriers experienced by psychiatric nurses to facilitate therapeutic relationships with mental healthcare users with dual diagnosis in a psychiatric hospital in Limpopo province, South Africa.DesignA qualitative, explorative, descriptive and contextual design was followed.MethodSemi‐structured interviews were conducted with 12 purposively selected participants who cared for mental healthcare users with dual diagnoses. Tech's method of open coding was used to analyse the data.FindingsDisruptive and disrespectful behaviour and mental healthcare users' substance use during hospitalisation resulted in nurses harbouring ambivalent feelings that impaired therapeutic nurse–patient relationships.ConclusionThe barriers affecting therapeutic relationships with mental healthcare users with dual diagnosis should be addressed to enhance recovery and treatment compliance.RecommendationsAn integrated approach with the involvement of the interprofessional team, debriefing and training for nurses may help to foster therapeutic nurse–patient relationships, empower nurses and enhance the recovery of mental healthcare users with dual diagnosis.