Linking to ClinicalTrials.gov

The National Library of Medicine invites you to link from your web site to ClinicalTrials.gov.

Use of ClinicalTrials.gov data is subject to Terms and Conditions. If you link to this site, please provide proper attribution to the U.S. National Library of Medicine (NLM) and ClinicalTrials.gov.

The data on ClinicalTrials.gov changes nightly. New studies are published and existing studies are updated every day. To ensure that the most up-to-date and accurate information is provided to the public, please do not make static copies of studies or search results. Instead, use a link to the ClinicalTrials.gov site to preform a new search or display the latest version of an existing study.

Linking to the ClinicalTrials.gov Home Page

The text below is the HTML for a link to the ClinicalTrials.gov home page. You can copy and paste the block of HTML directly into your web page. Please observe the form of the ClinicalTrials.gov name, which should always include an uppercase C and T, a lowercase g, no space between "Clinical" and "Trials."

This HTML:

<a href="http://clinicaltrials.gov" title="Information on Clinical Trials and Human Research Studies">ClinicalTrials.gov</a> provides patients, family members, and members of the public easy and free access to information on clinical studies for a wide range of diseases and conditions.

Displays this text in a browser:

ClinicalTrials.gov provides patients, family members, and members of the public easy and free access to information on clinical studies for a wide range of diseases and conditions.

Linking to Studies on ClinicalTrials.gov

Every study in ClinicalTrials.gov has a unique identifier refered to as an NCT Number. A specific study can be displayed with a link that ends with the NCT Number, like this:

http://clinicaltrials.gov/show/NCT00004451.

If you are looking at a study in ClinicalTrials.gov, the NCT Number can be found near the top and bottom of the Full Text View

This HTML:

<a href="http://clinicaltrials.gov/show/NCT00004451" title="Study NCT00004451"> Randomized Study of the Effects of Glucose on Cognition in Healthy Young and Elderly People and Parkinson's Disease Patients </a>

Displays this link in a browser:

Randomized Study of the Effects of Glucose on Cognition in Healthy Young and Elderly People and Parkinson's Disease Patients

Links that Search ClinicalTrials.gov

Links can be constructed that will search ClinicalTrials.gov. The results returned are the same as those produced by filling in the Advanced Search form and pressing the Search button. A specific search can be performed with a link that ends with search terms encoded as URL parameters, like this:

http://clinicaltrials.gov/search?cond=alzheimer's+disease

Standard URL encoding rules apply:

Parameter lists begin with a "?" character and are separated by "&" characters.
Spaces are replaced with "+" characters.
Special characters are replaced with a "%" followed by their ASCII code in hexadecimal.

The following parameters are recognized:

Param	Purpose
term	Generic search
cond	Targeted search for conditions
intr	Targeted search for interventions
outc	Targeted search for outcomes
spons	Targeted search for sponsors
recr	Restricts search results to open (recruiting or not yet recruiting) or closed (no longer recruiting) studies Two values are recognized: recr="open" and recr="closed"

Additional parameters are recognized, but are more likely to change over time. If you are an experienced HTML developer, and are willing to risk the possibility that your links will break, inspection of the HTML for the Advanced Search page will show you what parameters are currently in use.

Some Examples:

General search for the term, pediatric, in ClinicalTrials.gov

<a href="http://clinicaltrials.gov/search?term=pediatric>pediatric</a>

Targeted search for the condition, Diabetes, in ClinicalTrials.gov

<a href="http://clinicaltrials.gov/search?cond=diabetes">Diabetes</a>

For a multiword term that should be treated as a phrase, spaces must be replaced with "+" characters and the entire phrase enclosed in quotes, which are URL encoded as %22. For example:

Targeted search for the condition, Alzheimer's Disease, in ClinicalTrials.gov

<a href="http://clinicaltrials.gov/search?cond=%22Alzheimer's+Disease%22">Alzheimer's Disease</a>

A search with multiple clauses should have the parameters separated by an "&" character. For example:

Targeted search for open studies about treatment of PTSD with the drug, Fluoxetine, in ClinicalTrials.gov

<a href="http://clinicaltrials.gov/search?recr=open&cond=PTSD&intr=Fluoxetine">Fluoxetine</a>

Targeted search for the sponsor, NHLBI, in ClinicalTrials.gov

<a href="http://clinicaltrials.gov/search?spons=NHLBI">NHLBI</a>

Crawlers

ClinicalTrials.gov makes it easy for web crawlers to find all studies. Each time the study collection is updated, pages of links to all studies are generated.

Links to all studies

Most users will not find these pages useful.

XML Format

ClinicalTrials.gov provides data in XML format as shown below. Please note that use of ClinicalTrials.gov data is subject to our Terms and Conditions.

The simplest way to get data in XML format is to perform a search and use the download options at the bottom of the search results page. With the download options, you can retrieve XML for full studies or select fields (e.g. title, condition, lead sponsor, etc.) from the studies shown in your search result. The Display Options link, in the upper right of the search results page, lets you control which fields are shown and downloadable. Downloads produce a zip file which you can open in your browser or save to disk.

There are two forms of the XML for studies: one which includes the results information from records that have results and one which does not. Note that most trials do not contain results information as the results database was only launched in September 2008 and results information is only required for some completed trials.

Note that downloads of many studies can take several minutes.
The search results list can be obtained in XML format by appending a URL parameter, "displayxml=true", to the end of a search request URL.

Example: http://clinicaltrials.gov/search?term=%22lyme+disease%22&displayxml=true

By default, this option will return the first 20 search results. A parameter, "count=100", can be used to get the first 100 results. Another parameter, "start=101", can be used to get subsequent sets of studies.

In the following example, all three parameters are used to get results 1201-1400 out of more than 16,000 results found by a search of "cancer".

Example: http://clinicaltrials.gov/search?term=%22cancer%22&displayxml=true&count=200&start=1201

Caution: The XML for all studies is about 100 MB in size. If you attempt to display this much XML in your browser, your browser will probably freeze for several minutes and then crash.
An individual record can be obtained in XML format by appending a URL parameter, "displayxml=true", to the end of a show study URL. To include the results data, use the URL parameter, "resultsxml=true".

Example 1: http://clinicaltrials.gov/show/NCT00001372?displayxml=true

Example 2: http://clinicaltrials.gov/show/NCT00423098?resultsxml=true

The structure of this XML is defined by this XML schema.. The Document Type Definition (DTD) has been deprecated.
A zip file containing a set of protocol records in XML format can be downloaded by appending a URL parameter "studyxml=true" to the end of search request URL. To include both protocol and results XML, use the URL parameter "resultsxml=true". The resultsxml is a superset of the XML. Do not include both parameters.

Example 1: http://clinicaltrials.gov/search?term=%22lyme+disease%22&studyxml=true

Example 2: http://clinicaltrials.gov/search?term=lupus&resultsxml=true

Note that downloads of many studies can take several minutes.

Background Information