Giving a high dose of niacin to people with heart disease who are already taking a cholesterol-lowering statin does nothing more to prevent heart attacks and strokes, U.S. government researchers said on Thursday.

The findings from a large clinical trial challenge the notion that raising high-density lipoprotein, or HDL, the so-called “good” cholesterol, can further reduce heart risks in people who already have their “bad” cholesterol - low-density lipoprotein, or LDL - well under control.

Patients in the study who had a history of heart disease were treated with Abbott Laboratories’ Niaspan, a nearly $1 billion-a-year seller, and Merck & Co Inc’s Zocor, a statin available generically as simvastatin.

Researchers said Niaspan raised levels of HDL, the “good” cholesterol, but that did not translate into fewer fatal and non-fatal heart problems, prompting the National Heart, Lung, and Blood Institute to stop the study 18 months early. Abbott shares were down 2 percent on the news.

“Although we did not see the expected clinical benefit, we have answered an important scientific question about treatment for cardiovascular disease,” Dr. Susan Shurin, acting director of the National Heart, Lung, and Blood Institute, part of the National Institutes of Health, said in a statement.

Niacin, also known as Vitamin B3, has long been known to raise HDL and lower triglycerides, another type of blood fat that raises heart risks.

Millions of heart patients take niacin to raise HDL and lower triglycerides on the assumption that this will reduce heart risks, but it has not been clear that these treatments actually lower that risk. Heart disease is the world’s leading cause of death.

“This sends us back to the drawing board,” Shurin told a conference call.

“Either the approach to raise HDL was not effective, or HDL is not a good target,” she said.

DRUG RAISED HDL AS EXPECTED

The study, called the AIM-HIGH trial, enrolled 3,414 volunteers in the United States and Canada who were taking a statin to keep their LDL cholesterol low. More than half had suffered a heart attack before entering the trial.

All volunteers were given Zocor, and 515 participants were given a second LDL cholesterol-lowering drug, Merck’s Zetia, or ezetimibe, to make sure their LDL stayed in the target range of 40 to 80 milligrams per deciliter, which are very low levels.

Researchers said the drug performed as expected, raising HDL by about 28 percent and lowering triglycerides by about 25 percent, in keeping with other studies.

Late last month, an independent panel looked at the interim results of the study and concluded that high-dose niacin offered no benefits beyond statins alone in reducing heart complications, prompting the decision to end the study early.

There was also a slightly higher rate of strokes among patients who took niacin, but the overall rate of strokes in both groups was low.

Abbott, which reported Niaspan sales rose 8.4 percent to $927 million last year, said the relevance of the findings outside the type of patients in the study “is currently unknown and it would be premature to extrapolate these results to a broader patient population at this time.”

Wells Fargo Securities analyst Larry Biegelsen said the surprise findings could cut Niaspan sales by 20 to 30 percent.

The U.S. Food and Drug Administration says it will review the study but has made no new recommendations about niacin alone or in combination with statins.

The study is the latest to raise questions about whether increasing HDL helps prevent heart problems. With the success of statins to lower LDL, drugmakers have been looking to HDL-raising drugs as perhaps the next huge avenue for addressing cardiovascular disease.

One such promising drug, Pfizer Inc’s torcetrapib, was thought to be a potential huge seller by raising HDL through a different mechanism than niacin.

But torcetrapib was found to increase heart problems in one of the highest-profile flameouts in the drug industry’s history. Still, Merck and Switzerland’s Roche are developing drugs in the same class as torcetrapib.

And a study testing Abbott’s TriCor, or fenofibrate, a drug designed to lower triglycerides that also raises HDL, failed to cut heart problems in diabetics taking statins in the ACCORD trial despite improving both HDL and triglyceride levels.

(Reporting by Julie Steenhuysen in Chicago, additional reporting by Lewis Krauskopf and Bill Berkrot in New York; Editing by Eric Beech)

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By Julie Steenhuysen