People who survive a heart attack are urged to take statin drugs to prevent recurrent disease, but most patients in a large study either took less of the cholesterol-lowering medicines than needed or stopped taking them entirely within two years.

The study, in JAMA Cardiology, analyzed data on 29,932 Medicare patients ages 66 to 75 who had been hospitalized for a heart attack from 2007 through 2012 and had filled a prescription for either Lipitor or Crestor.

At six months after their discharge from the hospital, 58.9 percent of them were still taking the medicine with high adherence rates. By two years, only 41.6 percent were taking it as directed; many were taking lower dosages than prescribed, and nearly one in five had stopped taking the medicine completely.

The senior author, Dr. Robert S. Rosenson, a professor of medicine at the Icahn School of Medicine at Mt. Sinai, said that failing to take the medicine properly results in greater risk for heart attack, stroke and unstable angina.

“Health care providers have an obligation to educate the patient,” he said. “We need to stress the evidence that supports the therapy. People who continue the medicine have progressively fewer adverse outcomes over time. Once you have a heart attack, this is prevention for the rest of your life.”