Complementary and alternative medicine (CAM) is used as a complementary intervention in psychiatric healthcare. The reasons for using or not using CAM in psychiatric care in Sweden, and how such decisions are taken, are largely unknown. The aim was to investigate arguments for and against the use of CAM in Swedish psychiatric care, and how decisions are made. Interviews with 10 persons in decision-making positions in psychiatric health care were analysed thematically. The result shows diverging understandings of the evidence base for CAM. Arguments against CAM referred to scepticism, the importance of evidence-based practice and the obligation to follow national guidelines. Arguments in favour of CAM were that CAM was person-centred, safe, cost-effective, nursing interventions with positive effects, appreciated and demanded by patients, providing space for non-verbal communication and reflection, supporting the therapeutic alliance. Decision paths were described as top-down through a hierarchical structure, or bottom-up, driven by committed staff members. We discuss how detailed national guidelines should be to achieve equal and evidence-based care, while still allowing clinics to make local exceptions, adjusting the care according to clinical expertise and patients' preferences. Conclusion: Evidence-based, safe and cost-effective CAM methods may be relevant complementary interventions in psychiatric care, or as self-care, not to cure the psychiatric disease, but to reduce symptoms and promote sleep. With better knowledge of CAM, health professionals could guide patients through the jungle of CAM methods. Due to research problems on complex multicomponent interventions, high-quality pragmatic trials, including biomarkers, and qualitative studies are recommended.