Nearly one-third of the results of major studies published in three of the top medical journals between 1990 and 2003 have been refuted, according to a report in Wednesday's Journal of the American Medical Association (JAMA).
"Contradicted and potentially exaggerated findings are not uncommon in the most visible and most influential original clinical research," said John Ioannidis, author of the report and researcher at the University of Ioannina in Greece.
Ioannidis examined research appearing in the New England Journal of Medicine (NEJM), JAMA and The Lancet.
He found that subsequent research contradicted results of seven studies – 16 percent of his sample – and reported weaker results for seven others.
The contradicted studies dealt with a wide range of drugs and treatments – for instance Vitamin E pills have not been shown to prevent heart attacks, contrary to initial results.
"The crazy part about science and yet the exciting part about science is you almost never have something that is black and white," Catherine DeAngelis, JAMA's editor-in- chief, told the Associated Press.
Editors at NEJM added in a statement: "A single study is not the final word, and that is an important message."