Health is the most precious thing to preserve for. Wrong information related to health may be frustrating, misleading, and really dangerous sometimes. There are plenty of fake sites and under researched sites demonstrating some serious mistakes. Don't worry but there are some websites which not only provide authentic information, they are thoroughly researched and reviewed by related experts before publishing.
Medscape.com They have one of best websites for vast medical topics. They have wide range of network of certified professionals to review each and every topics. What to ask for? They generally provide all the information for free.
http://www.emedicine.com/ is also network group of medscape team.
http://www.webmd.com/ WebMD offers credible and reliable health information. They are updated regularly and articles are reviewed by experts before publishing. It is one of the most cited one for obtaining medical information.