© 2022 John Wiley & Sons Ltd.What is known on the subject?: Medicinal plants are a part of everyday life. Medicinal plants have many effects on the lives of individuals diagnosed with mental illness. What the paper adds to existing knowledge?: Since there is no qualitative study in which individuals diagnosed with mental illness provided a detailed explanation of their views about the use of medicinal plants, this study will fill a gap in the literature and guide mental health nurses. This study provides information for mental health nurses about how individuals diagnosed with mental illness evaluate medicinal plants, what it means to them and the effects of medicinal plants. It provides ideas about the use of medicinal plants as a tool to protect and improve mental health. In addition, since the majority of the studies on mental illnesses and medicinal plants are quantitative studies, it was thought that this study was different from the seminal studies in the literature and could offer new ideas for future studies. What are the implications for practice?: The results of this study show mental health nurses that the positive aspects of medicinal plants can be used to maintain and improve the mental health of individuals diagnosed with mental illness. Mental health nurses should evaluate the treatment and maintenance process in detail, considering that medicinal plants may interact with drug treatment or the risks of using medicinal plants in terms of adverse effects. Moreover, mental health nurses should fight against the negative aspects of medicinal plants. Mental health nurses and individuals diagnosed with mental illness should be made aware of the use of medicinal plants. Abstract: Aim: There was no qualitative study found in which individuals diagnosed with mental illness explained their views in detail about the use of medicinal plants. It is therefore thought that this study will fill this gap in the literature and guide mental health nurses in the field. The research was carried out to determine the use of medicinal plants by individuals diagnosed with mental illness. Method: This research was a qualitative study conducted using the case study design. Ten individuals diagnosed with mental illness for at least 10 years, determined by the purposeful sampling method were interviewed. The data were collected between March and April 2022 with information form and semi-structured interview form and analysed with the content analysis method. Findings: Four of the participants had depression, four had anxiety and two had mood disorders. Themes were determined to be a source of healing (ointment for the soul, body tonic and organic and nature's miracles) and cultural accumulation (faith and inheritance, counselling helpline). Conclusion: Participants described medicinal plants as a source of healing, stating that medicinal plants are good for bodily and mental health and provide purification. Individuals stated that the information about medicinal plants represents cultural accumulation as an inheritance, they applied them as a counselling helpline in case of illness. Implications for Practice: The positive effects of medicinal plant use can be supported by mental health nurses. Considering that medicinal plants may interact with the drug treatment, the use of medicinal plants should be evaluated in detail by mental health nurses.