Health Topics
Official websites use .gov
A
.gov website belongs to an official government
organization in the United States.
Secure .gov websites use HTTPS
A
lock (
) or https:// means you’ve safely connected to
the .gov website. Share sensitive information only on official,
secure websites.
The National Library of Medicine is making every effort to ensure that the information available on our Web site is accessible to all. If you use special adaptive equipment to access the Web and encounter problems when using our site, please let us know. Contact Customer Service or phone us at (888) FIND-NLM (346-3656) or (301) 594-5983 and provide the address (URL) of the page on which you need assistance, along with a description of the problem.