Physicians should curb prescriptions for the 80-milligram dose of the cholesterol-lowering statin drug simvastatin due to risk of muscle injury, the Food and Drug Administration said Thursday.

The agency advises that only patients who have been on the 80-milligram version of the drug for a year or more without consequence should continue to take it. If physicians find that 40 milligrams is not adequately controlling a patient’s LDL levels, the FDA says a different statin should be employed instead.

Simvastatin’s brand name is Zocor. It is widely used because it is less expensive than other options. The FDA estimates that about 2.1 million people were prescribed a medication containing 80 milligrams of simvastatin last year.

All statin drugs carry the risk of causing an injury known as myopathy, which causes muscle weakness and pain, according to the FDA. But the risk is higher at more than 80 milligrams since myopathy can occur when simvastatin interacts with other medications. The FDA notes that the benefits of statins generally outweigh the risks presented by the side effects, and cautions patients not to stop taking statins without consulting a doctor.