Each ClinicalTrials.gov record presents summary information about a study protocol and includes the following:

- Disease or condition
- Intervention (for example, the medical product, behavior, or procedure being studied)
- Title, description, and design of the study
- Requirements for participation (eligibility criteria)
- Locations where the study is being conducted
- Contact information for the study locations
- Links such as MedlinePlus® for patient health information and PubMed® for citations and abstracts for scholarly articles

Some records also include information on the results of the study, such as:

- Description of study participants (that is the number starting and completing the study and their demographic data)
- Outcomes of the study
- Summary of adverse events experienced by study participants

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ClinicalTrials.gov provides information on clinical studies. Information is provided and updated by the sponsor or principal investigator of the clinical study. Studies are generally submitted when they begin and updated throughout the study. In some cases, results of the study are submitted after the study ends.

ClinicalTrials.gov includes information about medical studies in human volunteers. Most of the records describe clinical trials (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. ClinicalTrials.gov also includes records describing observational studies and programs providing access to investigational drugs outside of clinical trials (expanded access).

Studies listed in the database are conducted in 182 countries. ClinicalTrials.gov does not contain all clinical studies conducted in the United States because not all studies are required by law to be registered. However, the number of studies registered each year has increased over time as more policies and laws requiring registration have been enacted and as more sponsors and investigators voluntarily register their studies.