It is a good idea to register your protocol in a publicly accessible way. This will help avoid other people completing a review on your topic. Similarly, before you start doing a systematic review, it's worth checking the different registries that nobody else has already registered a protocol on the same topic.
This page lists mains sources of registered protocols.
PROSPERO is an international database of prospectively registered systematic reviews in health and social care, welfare, public health, education, crime, justice, and international development, where there is a health related outcome. Key features from the review protocol are recorded and maintained as a permanent record. PROSPERO aims to provide a comprehensive listing of systematic reviews registered at inception to help avoid duplication and reduce opportunity for reporting bias by enabling comparison completed review with what was planned in the protocol.
The Cochrane Library is a database that contain different types of high-quality, independent evidence to inform healthcare decision-making. Search the Cochrane Library for any published protocols or reviews related to your topic of interest before you propose and register a new review.
The Open Science Framework is a free and open source project management tool that supports researchers throughout their entire project life cycle. It has been developed by the Center for Open Science with a mission is to increase openness, integrity, and reproducibility of research.
Amongst other initiatives, it offers preregistration - you can specify your research plan in advance of your study and submit to to a registry.
JBI is recognized as a global leader in evidence-based healthcare. The Institute and its collaborating entities promote and support the synthesis, transfer and utilization of evidence through identifying feasible, appropriate, meaningful and effective healthcare practices to assist in the improvement of healthcare outcomes globally.
The JBI EBP database is a comprehensive range of resources including over 3,000 records across seven publication types: Evidence Summaries, Evidence-Based Recommended Practices, Best Practice Information Sheets, Systematic Reviews, Consumer Information Sheets, Systematic Review Protocols, and Technical Reports.
The Research Registry offers registration for all types of research studies, from case reports to observational/interventional studies to systematic reviews and meta-analyses.
Whilst the focus in the past has been on registering randomised controlled trials (RCTs), there has been tremendous growth in observational studies (case series, cohort, case-control, cross-sectional, etc), many of which are not registered. Whilst some trial registries do allow for the registration of observational studies, only a small fraction are actually registered.