Cholesterol-lowering drugs continue to produce benefits without any serious safety problems, such as increased cancer risk, even after more than a decade of use, researchers said Wednesday.

The finding from a large British clinical study following patients for 11 years provides reassurance for people at risk of heart attacks who are typically prescribed such medicines indefinitely.

So-called statin drugs are not without side effects. They can cause nausea, muscle pain, and occasional kidney and liver damage.

But long-term follow-up in the 20,000-patient Heart Protection Study (HPS) found no evidence that statins increased the risk of non-vascular mortality or made patients more likely to develop cancer.

Richard Bulbulia of the University of Oxford's Clinical Trial Service Unit, one of the leaders of the trial, said the persistence of the benefit and the long-term evidence of safety was "remarkable."

Outside experts agreed it was reassuring. Some past studies have indicated a possible cancer risk with statins, although a major analysis by U.S. researchers three years ago concluded there was no causal link.

"Concerns should be put to rest, and doctors should feel reassured about the long-term safety of this life-saving treatment for patients at increased cardiovascular risk," Payal Kohli and Christopher Cannon of Boston's Brigham and Women's Hospital wrote in a commentary in the Lancet medical journal, which published the results online.

The HPS study assessed the benefits of 40 milligrams daily of simvastatin, the active ingredient of Merck & Co's now off-patent drug Zocor, or placebo.

It found a 23 percent reduction in heart attack, stroke and vascular disease after five years in those on treatment -- and the benefit persisted largely unchanged for a further six years when statin use, which was encouraged, was similar in both groups of patients.

Other popular statin medicines include Pfizer's top-selling Lipitor, which is due to lose patent protection in the United States at the end of this month, and AstraZeneca's Crestor.