Comparative Clinical Research on Homeopathy: A Series of Systematic Reviews with Meta-Analyses (HOMA)–Project Outline

Background: Only a few meta-analyses are available on the therapeutic or preventive effects of homeopathic medicinal products (HMPs) in specific health conditions. The HOMA project aims to conduct systematic reviews (SRs) and meta-analyses (MAs) on the clinical efficacy and real-world effectiveness of HMPs for 12 clinical indications and of two medicines. Methods: First, a framework study will provide an overview of the applicability of different evidence synthesis tools to homeopathy, as well as other whole system approaches. A template protocol will define the methods that will be applied to the 14 SRs. Eligible studies need to include patients treated therapeutically or preventatively with any kind of HMP (individualized, clinical, complex). Peer-reviewed studies, as well as grey literature, of randomized and non-randomized comparative studies in various languages will be selected. Risk of bias will be assessed using ROB-2 and ROBINS-I. Reporting quality, model validity, and generalizability will be evaluated using a specially developed critical appraisal tool of homeopathic intervention studies (CATHIS). If a meta-analysis is possible and feasible, the complexity of interventions and heterogeneity of the study pool will be examined in various analytical steps. The GRADE approach will be used for assessing the certainty of evidence. The 14 SRs will be conducted by multidisciplinary teams comprising methodologists, homeopaths, and clinicians with expertise in the specific indications under review. Results: The template protocol will be registered in spring 2025 and then published. The protocols for the 14 SRs will be registered separately. The framework study and the 14 SRs will be conducted and published sequentially during a period of 4 years, starting in 2025. Conclusion: This series of SRs and MAs aims to establish a reliable evidence base to support informed discussions about the efficacy and effectiveness of homeopathic medicinal products, and to identify topics for further research.