Drug maker Amarin (AMRN) is supposed to hear next week whether it won U.S. approval to sell a heart drug derived from fish oil. But there was heavy trading in the stock Thursday, at least in part due to a website that indicated the drug was approved by the Food and Drug Administration.

The website wasn't supposed to go live and it was pulled shortly after it was discovered and passed around on Twitter. "FDA-approved and available soon," the website said. It also showed the brand name, Vascepa (the drug has been known simply as AMR101). The name is pronounced vas-EE-puh, according to the site.

The drug is aimed at treating high levels of triglycerides (a type of fat in the blood). Investors have bid up the stock this year in anticipation of an FDA approval. The agency is scheduled to make a decision July 26.

American shares of Dublin, Ireland, Amarin rose as high as $15.87 in morning trading before closing at $15.36. The stock has doubled this year.

Amarin addressed the slip in a securities filing Thursday, blaming a third party for the mishap:

On July 19, 2012, information related to AMR101, Amarin Corporation plc’s ("Amarin") lead product candidate, and its pending regulatory review with the U.S. Food and Drug Administration (“FDA”) was inadvertently published through a draft website that is under design by third parties on behalf of Amarin. The information was outdated and should not be relied upon as accurate. AMR101 review at FDA is still pending. No determinations have been made by FDA on its review of the AMR101 New Drug Application.

A spokeswoman at the FDA declined to comment, citing agency policy not to talk about pending applications.

It was the second time in a week that news of a pending drug approval was released prematurely. USA Today published online, and then retracted, a story Tuesday saying that Vivus (VVUS) diet pill was approved. An official announcement was made later that evening. (See Vivus Wins US Approval to Sell New Diet Drug Qsymia.)