Defining psychiatric and mental health nursing has been a challenge for decades, and it is still difficult to find a comprehensive definition. We have identified a possibility to clarify psychiatric and mental health nursing based on humanistic philosophy in a general psychiatric care context. The aim was therefore to identify and synthesize the theoretical frameworks from which psychiatric and mental health nursing models are developed. We systematically collected and evaluated articles based on Grounded Theory (GT) methodology regarding psychiatric or mental health nursing. The PRISMA statement for systematic reviews was used and the formal process of synthesis, as a three-step process of identifying first -, second - and third-order themes following the examples of Howell Major and Savin-Baden. The synthesis resulted in a model describing five core elements of psychiatric and mental health nursing: ‘professional nursing’, ‘therapeutic relationships’ and ‘honest engagement’, with time as the all-encompassing theme, including the patients’ ‘lifetime perspective’. Psychiatric and mental health nursing is a caring support towards recovery, where the patient’s lifetime perspective must be in focus during the caring process with a relationship built on an honest engagement. Time is therefore essential for psychiatric and mental health nursing.