Objective To develop understandings of the nature and influence of trust in the safe management of medication within mental health services. Setting Mental health services in the UK. Method Qualitative methods were applied through focus groups across three different categories of service user—older adult, adults living in the community and forensic services. An inductive thematic analysis was carried out, using the method of constant comparison derived from grounded theory. Main Outcome Measure Participants’ views on the key factors influencing trust and the role of trust in safe medication management. Results The salient factors impacting trust were: the therapeutic relationship; uncertainty and vulnerability; and social control. Users of mental health services may be particularly vulnerable to adverse events and these can damage trust. Conclusion Safe management of medication is facilitated by trust. However, this trust may be difficult to develop and maintain, exposing service users to adverse events and worsening adherence. Practice and policy should be oriented towards developing trust.