Doctors critical of the manufacturer Merck and its reporting of Vioxx studies have long argued the increased heart risks started after just a few months use. But the company continues to insist the risks didn't increase until after about 18 months of use.
A company spokesman says this study is small and has several limitations.
Also in the report is the finding that other drugs in the same class of painkillers, known as COX-2 inhibitors, may cause similar harm.
