What happened

Shares of Amarin (AMRN -1.43%) were trading down by 8.2% as of 11:03 a.m. ET Friday after having fallen by as much as 19.2% earlier in the session. It was the second consecutive day of declines after additional data from an exploratory post hoc sub-analysis from the company's Reduce-It cardiovascular outcomes study of Vascepa were published on the website of the medical journal Circulation

So what

The published data wasn't great news for the biotech company. The study's findings raise doubts about whether or not Vascepa is actually effective in preventing heart attacks.

Some experts are even advocating that the Food and Drug Administration (FDA) should reevaluate its previous approval of the drug, according to STAT, a news organization that covers the biopharmaceutical industry. Others believe that Amarin should conduct a new clinical study.

However, Amarin appeared to try to brush off the latest results.

"While exploratory biomarker sub-analyses are interesting scientifically, what is most clear and important clinically are the cardiovascular outcomes results seen in the Reduce-It trial overall," Chief Medical Officer Nabil Abadir stated in a press release.

Vascepa first won FDA approval in 2012 as a treatment to reduce triglyceride levels in patients with severe hypertriglyceridemia. The FDA expanded the approval in 2019 to allow it to be prescribed for the reduction of cardiovascular risks, including the risks of heart attack and stroke. This second approval was based on the results of the Reduce-It study.

Now what

Amarin is already struggling in the U.S. market because of generic competition for Vascepa. It remains to be seen if the FDA will take further action based on the post hoc sub-analysis findings.