Aim: To develop clinical practice recommendations for nurse-administered intramuscular injections in mental health. Background: Intramuscular injection is the main route of long-acting injectable antipsychotics’ administration that appear to improve the long-term prognosis of mental illness. Specific guidelines related to the nurse administration of intramuscular injections need to be updated and to explore not only the technical aspects of this procedure. Design: A modified RAND/University of California Los Angeles (UCLA) appropriateness method Delphi study was conducted between October 2019 and September 2020. Methods: A multidisciplinary steering committee conducted a literature review and developed a list of 96 recommendations. These recommendations were submitted in a two-round Delphi electronic survey to a panel of 49 experienced practicing nurses from five mental health hospitals in France. Each recommendation was rated for its appropriateness and applicability in clinical practice on a 9-point Likert scale. Consensus among nurses was evaluated. The steering committee discussed the results after each round and approved the final set of recommendations. Results: A final set of 79 specific recommendations were accepted for their appropriateness and applicability in clinical practice. Recommendations were classified in five domains: legal and quality assurance aspects, nurse-patient relationship, hygiene, pharmacology, and injection technique. Conclusion: The established recommendations placed patients at the heart of the decisions concerning the intramuscular injection and underlined the need for specific training programs. Future research should focus on the integration of these recommendations in clinical practice, by both before-and-after studies and regular assessments of professional practices with relevant indicators. Impact: The recommendations developed for good nursing practices explored not only the technical aspects but integrated the nurse-patient relationship. These recommendations may impact usual practices of administration of long-acting injectable antipsychotics and most of them could be applied in many countries. No Patient or Public Contribution: Due to the study design.