LibGuides: Grey Literature: Clinical trials/Registered research

What is a clinical trial?

"A clinical trial is any research study that prospectively assigns human participants or groups of humans to one or more health-related interventions to evaluate the effects on health outcomes. Clinical trials may also be referred to as interventional trials. Interventions include but are not restricted to drugs, cells and other biological products, surgical procedures, radiologic procedures, devices, behavioural treatments, process-of-care changes, preventive care, etc. This definition includes Phase I to Phase IV trials."

This definition comes from the World Health Organization's ICTRP Glossary page:

Glossary. (n.d.). Retrieved May 30, 2025, from https://www.who.int/tools/clinical-trials-registry-platform/about/glossary

Why include them in your search?

If you are exploring a topic that is looking at medical/health interventions, then you should consider searching for clinical trials. As the definition on this page explains, the intervention could by anything: drugs/pharmaceuticals, cells and other biological products, surgical procedures, radiologic procedures, devices, behavioural treatments, process-of-care changes, preventive care, etc.

Be aware, there will be challenges finding clinical trials and their outcomes

The AllTrials campaign website sums it up best:

Approximately half of all the clinical trials ever conducted have never been reported, and even with a lot of improvement and advocacy over the past decade, the goal of having 100% of trials registered and reporting continues.

Why this is important?

If only some of the results of clinical trials regarding specific health care interventions are published (those with positive results), then the evidence we have is distorted, because important results (like the negative ones) are missing. Additionally, if the results of these studies are not recorded then this effort is wasted: it results in poorly informed treatment decisions, lost opportunities to progress potentially life-saving research, and wasting resources on dead-end research and repeated trials.

Alltrials—Sense about science. (2020, February 12). https://senseaboutscience.org/alltrials/

Where to find clinical trials and registered research

Clinical trials can be found through searching clinical trial registers. These are listed alphabetically.

Center Watch Clinical Trials
Online database of industry-sponsored global clinical trials actively seeking study volunteers.
ClinicalTrials.gov
A database of privately and publicly funded clinical studies conducted around the world.
Cochrane Central Register of Controlled Trials (CENTRAL)
A highly concentrated source of reports of randomized and quasi-randomized controlled trials. Most CENTRAL records are taken from bibliographic databases (mainly PubMed and Embase.com), but records are also derived from other published and unpublished sources, including CINAHL, ClinicalTrials.gov and the WHO's International Clinical Trials Registry Platform. CENTRAL first began publication in 1996, but its composite nature means that it does not have an inception (start) date, in the way that other traditional biomedical databases do.
EU Clinical Trials Register
The EU Clinical Trials Register contains information on interventional clinical trials on medicines conducted in the European Union (EU), or the European Economic Area (EEA) which started after 1 May 2004.
GSK Clinical Studies Register
Clinical studies sponsored by pharmaceutical company Glaxo Smith Kline.
ICTRP Search Portal
World Health Organization International Clinical Trials Registry Platform. The Clinical Trials Search Portal provides access to a central database containing the trial registration data sets.
ISRCTN Registry
The ISRCTN registry is a primary clinical trial registry recognised by WHO and ICMJE that accepts all clinical research studies (whether proposed, ongoing or completed), providing content validation and curation and the unique identification number necessary for publication. All study records in the database are freely accessible and searchable. The registry aims to include all interventional and non-interventional clinical studies that prospectively involve UK participants and evaluate biomedical or health-related outcomes.