Why and Where to Register Your Systematic Review Protocol

Registering a protocol is the step that converts your good intentions into evidence. You can tell reviewers you set your criteria before seeing the results, but a public, time-stamped registration proves it. That is the whole reason the practice exists, and it is why journals increasingly ask for a registration number before they will consider your review.

Most people know PROSPERO. Fewer know that it is one of several registers, that it turns away certain review types, and that choosing the right home for your protocol depends on what kind of review you are running.

The short answer

Register your protocol to create a public record of your plan before your results are known. This prevents outcome-switching, reduces duplicated effort, and satisfies journal requirements. PROSPERO is the main register for health-related systematic reviews. For reviews it does not accept, or for non-health topics, alternatives include INPLASY, the Research Registry, OSF Registries, and protocols.io. Some journals also publish protocols as citable articles.

Register prospectively, before formal screening. Registering after the fact carries far less weight, because it no longer proves your plan predated your findings.

Why registration matters

Three benefits, and they reinforce each other.

It prevents bias. Once you have seen your search results, it is tempting to adjust your outcomes or criteria toward a cleaner story. A registered protocol removes that option by fixing your plan in public beforehand. Anyone can later compare what you registered against what you reported.

It reduces duplication. A register lets others see which reviews are already underway. That helps you avoid spending a year on a question someone else is about to answer, and helps them avoid duplicating yours.

It satisfies journals. Many journals now require or strongly expect a registration number, and reviewers treat an unregistered review with more suspicion. Registration is fast becoming a baseline expectation rather than a nicety.

The common thread is trust. Registration is how you demonstrate, rather than merely assert, that your review followed a plan set while you were still neutral.

Where to register: the options

PROSPERO is the International Prospective Register of Systematic Reviews, run by the Centre for Reviews and Dissemination at the University of York. It is free and the most widely recognized register, but it only accepts systematic reviews with a health-related outcome, and it excludes scoping and literature reviews. It is also prospective-only in practice, with eligibility ending once you complete data extraction. For most health-related systematic reviews, this is the default choice. We cover it in detail in PROSPERO registration: a complete walkthrough.

INPLASY (International Platform of Registered Systematic Review and Meta-analysis Protocols) is a register specific to systematic reviews and meta-analyses. It accepts a broad range of review protocols and issues a DOI. Unlike PROSPERO, it charges a fee, and it will accept retrospective registration in some cases, though prospective registration is always the stronger practice.

Research Registry maintains a registry of systematic reviews and meta-analyses alongside its other study registers. Like INPLASY, it accepts systematic review protocols and is an option when PROSPERO does not fit.

OSF Registries (Open Science Framework) is a general-purpose register that accepts almost any study type, including scoping reviews and non-health reviews that PROSPERO turns away. It is free and flexible, which makes it the common fallback for review types outside PROSPERO's scope.

protocols.io is another general platform that lets you publish and time-stamp a protocol across many research types. It suits reviews that do not fit a review-specific register.

Journal publication. Some journals publish systematic review protocols as peer-reviewed, citable articles. This gives your protocol a permanent, referenceable form and a degree of peer scrutiny, though it is slower than filling in a register.

Registers compared

How to choose

Start from your review type. If you are running a health-related systematic review, PROSPERO is the natural home, free and widely recognized. If your review falls outside its scope, a scoping review, a non-health topic, or one that PROSPERO has declined, use OSF Registries or another general register rather than skipping registration. If a citable, peer-reviewed protocol matters for your project, consider publishing it in a journal that accepts them.

Whatever you choose, register prospectively. The value of a register comes entirely from the timing, a plan recorded before the answer is known. A late registration is far weaker, and in PROSPERO's case an impossible one once data extraction is done.

Common mistakes

Skipping registration entirely. Even when no journal demands it, an unregistered review is harder to trust. Registration is cheap insurance for your credibility.

Assuming PROSPERO takes everything. It does not accept scoping or literature reviews. Check eligibility before you invest time in the form, and use an alternative if your review does not fit.

Registering too late. A registration filed after you have seen your results proves nothing about your original plan. Register before formal screening.

Registering from a half-formed plan. A register asks for your criteria, outcomes, and analysis. Write the protocol first so registration is just transcription. See how to write a systematic review protocol.

Never updating the record. Registrations are meant to track the review through to publication. Update the status and link the finished review.

Frequently asked questions

Do I have to register my systematic review protocol? Not universally, but it is standard good practice and many journals require it. Registration demonstrates that your plan predated your results.

Where can I register if PROSPERO rejects my review? OSF Registries accepts a broad range of review types, including scoping and non-health reviews. INPLASY and the Research Registry are other options for systematic reviews.

Is protocol registration free? PROSPERO and OSF are free. INPLASY and the Research Registry charge a fee. Journal protocol publication costs vary.

Can I register after starting the review? Prospective registration is far stronger. Some registers accept retrospective registration, but PROSPERO does not once data extraction is complete, and a late registration carries less weight everywhere.

What is the difference between registering and publishing a protocol? Registration records your plan in a database. Publishing a protocol puts it in a peer-reviewed, citable article. Both time-stamp your plan; publication adds peer scrutiny and a permanent reference.

The bottom line

Registering your protocol proves your plan came before your results, which is the foundation of a trustworthy review. Register prospectively, before formal screening, and pick the register that matches your review type: PROSPERO for health-related systematic reviews, OSF or another general register for the reviews it does not accept, and journal publication when a citable protocol helps.

The specific register matters less than the act itself and the timing. Get a time-stamped plan on the record, then hold to it. For the PROSPERO-specific process, see our walkthrough.

Protocol registered and ready to go? Verflux runs the review your registration describes, from search to meta-analysis.