The Food and Drug Administration warned Wednesday that the highest dose of a popular cholesterol-lowering drug should no longer be prescribed to new patients because of concerns that it can cause muscle damage.

The highest-approved dose — 80 milligrams — of the cholesterol-lowering drug simvastatin can increase the risk for myopathy, which is a form of muscle damage, the agency said.

As a result, the agency is recommending that doctors only continue prescribing that dose in patients who have been taking it for at least a year without experiencing problems. In addition, it should not be taken with some other drugs, including some antibiotics, HIV drugs and anti-fungal medications, according to the FDA and Merck, which makes the drug.

In 2010, about 2.1 million patients in the United States were prescribed a product containing simvastatin at that dose, the agency said. About 12 percent of simvastatin users take that dose, according to Merck.

“The FDA has completed its review of the safety of high-dose simvastatin and is making label changes to reduce the risk of statin-associated muscle injury,” said Eric Colman of the FDA’s Center for Drug Evaluation and Research, in a statement. “We want to ensure that patients and health care professionals are aware of the new labeling changes to simvastatin, including the increased risk of myopathy when using the 80 mg dose of simvastatin.”

The changes were based on the FDA’s review of the results of a seven-year study, an analyses of adverse events that the agency had received among patients taking the drug and other research that indicated that patients taking that dose were at greater risk than those taking lower doses or other similar cholesterol-lowering drug, the agency said.

Simvastatin is sold alone under the brand name Zocor and as a generic product. It is also sold in combination with another drug known as ezetimibe under the brand name Vytorin, and in combination with niacin under the brand name Simcor.

“Nothing is more important to Merck than the safety of our medicines and the well-being of the patients who take them,” said Michael Rosenblatt, Merck’s chief medical officer, in a statement. “We are proud of the role that simvastatin plays along with a healthy diet for patients with high cholesterol and those at high risk for heart attacks and strokes.”