UPDATE 2-U.S. FDA tackles gray area of social media

* More than 800 people tried to register for FDA event

* Lilly, Yahoo call for 'clarity' on FDA guidelines

* FDA urged to communicate with Wikipedia, other sites (Recasts more comments from Google, Yahoo, Johnson & Johnson)

By Deepa Seetharaman

WASHINGTON, Nov 12 (Reuters)- Drug makers, Internet companies and nonprofits called for clarity on what is a gray area for U.S. health regulators: how drug promotion on Twitter, Wikipedia, blogs and other social media can be regulated.

The two-day Food and Drug Administration hearing aims to find out if the agency needs to specifically regulate how drugs and medical devices it oversees are promoted on the Internet.

"The lack of clarity today is creating confusion among the advertising community," said David Zinman, vice president at Yahoo Inc (YHOO.O).

The FDA already has strict rules governing what drug makers can say in magazine, newspaper and television advertisements, but the fast-evolving online world is a Wild West when it comes to what is -- and is not -- possible to regulate.

In April, the FDA sent warning letters to 14 companies including Eli Lilly and Co (LLY.N) and Merck & Co Inc (MRK.N) about their drug marketing online, saying that ads for certain products were misleading and did not contain any risk information.

Since those letters, pharmaceutical companies have changed the way they design their ads and no longer include the brand name, Google Inc (GOOG.O) and Yahoo representatives said.

Google officials said the click-through rate on these ads "dramatically decreased" after April. They offered another ad design that offers consumers links to risk information.

"Users see all these links and they don't know exactly where they're going until they get there," Zinman said.

TACKLING TRICKY QUESTIONS

More than 800 people tried to register for the event, which was held in a conference room that seats 350. Others followed the speeches online and posted messages about it on Twitter.

The FDA organized about 30 different presentations on Thursday on topics ranging from drug makers' role in monitoring Internet content to data on how consumers get their health news.

Participants were asked to consider a number of questions, including how much responsibility drug makers bear for online content about their products and how to determine when online chats about a medicine are influenced by the manufacturer.