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Overview is a Web-based resource that provides patients, their family members, health care professionals, researchers, and the public with easy access to information on publicly and privately supported clinical studies on a wide range of diseases and conditions. The Web site is maintained by the National Library of Medicine (NLM) at the National Institutes of Health (NIH). Information on is provided and updated by the sponsor or principal investigator of the clinical study. Studies are generally submitted to the Web site (that is, registered) when they begin, and the information on the site is updated throughout the study. In some cases, results of the study are submitted after the study ends. This Web site and database of clinical studies is commonly referred to as a "registry and results database." contains information about medical studies in human volunteers. Most of the records on describe clinical trials (also called interventional studies). A clinical trial is a research study in which human volunteers are assigned to interventions (for example, a medical product, behavior, or procedure) based on a protocol (or plan) and are then evaluated for effects on biomedical or health outcomes. also contains records describing observational studies and programs providing access to investigational drugs outside of clinical trials (expanded access). does not contain information about all the clinical studies conducted in the United States because not all studies are required by law to be registered (for example, observational studies and trials that do not study a drug, biologic, or device). See FDAAA 801 and the Final Rule for more information. However, the rate of study registration has increased over time as more policies and laws requiring registration have been enacted and as more sponsors and investigators have voluntarily registered their studies. was made available to the public on February 29, 2000, and the results database was released in September 2008. Once a study is registered on the site, it is not removed. The full history of the changes made to a record can be accessed by clicking on the History of Changes link near the bottom of the full text view of each record.

An account of the development and expansion of in response to changes in policies and laws is provided on the History, Policies, and Laws page.

Searching does not require registration or personal identification. Because is a Government Web site, it does not host or receive funding or advertising from commercial entities or display commercial content. Statistics received more than 215 million page views per month and 145,000 unique visitors daily (as of April 2019).

The following statistics are updated daily:

  • currently contains 499,014 study records. Of these, 67,195 studies are recruiting participants. Studies are sponsored by NIH, other Federal agencies, nonprofit organizations, and private industry.
  • Studies listed in the database are conducted in all 50 States and in 222 countries.

For more statistics, charts, and maps related to, see the Trends, Charts, and Maps page.

Who Uses

The main users of the site are patients, their families and caregivers, health care professionals, clinical researchers, and study record managers. They use to:

Clinical researchers also use the site to stay current on developments in their field of interest, find collaborators, and identify unmet research needs. Other researchers may use the site to compile information on the research being conducted in a particular area to support the development of practice guidelines or reviews of completed research. In addition, clinical researchers or their study record managers must register their studies and submit study results to using a Web-based system called the Protocol Registration and Results System. For more information, see:

Related Journal Publications

Awards Wins the Innovations in American Government Award

In 2004 was cited by the Ash Center for Democratic Governance and Innovation at the Harvard Kennedy School as "a successful model for the creation and maintenance of a system that processes and presents large amounts of specialized information to a wide range of users" and was selected as one of five award winners. The Innovations in American Government Awards is the Nation's preeminent program devoted to recognizing and promoting excellence and creativity in the public sector. The program highlights exemplary models of government innovation and advances efforts to address the Nation's most pressing public concerns.


For more information, including interview requests, please contact the NLM Office of Communications and Public Liaison at

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This page last reviewed in May 2021