WASHINGTON (AP) -- Federal health advisers dealt a major blow to specialty drugmaker Amarin Corp. on Wednesday, saying that the government should delay expanding approval of the company's prescription fish-oil drug until more patient data is available.

The Food and Drug Administration's panel of outside advisers voted 9-2 against recommending broader use of Vascepa, a form of fish oil designed to lower triglycerides, a type of fat in the bloodstream.

A majority of panelists said that while Vascepa significantly lowers fat levels, it is unclear whether that actually translates into fewer heart attacks for patients. The vote suggests that experts are looking for more meaningful evidence of benefits with fat and cholesterol-lowering drugs, which could signal a higher bar for future treatments.

"I'm optimistic about the data presented today by Amarin," said Dr. Brendan Everett of Harvard Medical School, who voted against the drug. "I am wary, however, of approving a drug that has a potential market of tens of millions of people without hard efficacy data."

The panel members said the FDA should delay a decision on expanding the drug's use until Amarin completes a study of heart attack rates in patients. Results from that study are not expected until 2015 or 2016.

"Given there is an ongoing trial underway, it makes sense to wait for those outcomes," said Dr. Edward Gregg, of the Centers for Disease Control and Prevention.

The FDA is not required to follow the recommendations of its advisory panels, though it often does.

Vascepa was approved in 2012 for patients with unusually high triglyceride levels, but Amarin wants to get a broader marketing approval. It has asked the FDA to allow marketing of the drug for patients with high triglyceride levels and heart disease who are already taking a statin drug to help control their cholesterol. Statins are the most widely prescribed cholesterol drugs in the world.

The FDA is scheduled to make a ruling on Vascepa by Dec. 20.

Hanging over the day's discussion were several recent studies that failed to show meaningful medical benefits for patients taking other popular cholesterol medications.

In 2011, federal scientists halted a large government study of Niaspan, a prescription form of niacin, after preliminary results showed the pill failed to prevent heart attacks or strokes. Niacin is a form of vitamin B that boosts good cholesterol, which has been shown to fight artery buildup. But that benefit didn't translate into fewer heart attacks among patients with a history of heart disease.

Only a few months earlier, a study of another cholesterol pill, Trilipix, showed that diabetic patients taking the drug plus a statin had just as many heart attacks as patients taking a statin alone. Trilipix is a fibrate, a drug that lowers triglycerides while boosting HDL or "good cholesterol" levels.

Vascepa is a prescription strength form of an omega-3 fatty acid found in wild fish harvested from the Pacific Ocean. Amarin's marketing materials state that four capsules of Vascepa is the equivalent of taking 10 to 40 over-the-counter fish oil supplement capsules.

Shares of Ireland-based Amarin Corporation plc were halted from trading Wednesday ahead of the meeting. The stock has lost more than half its value in the past year.