from reuters.com: Next time a research finding leaves you slack-jawed, thinking it's too good to be true, you might just be right, according to a massive new analysis tracking the fate of splashy medical studies. It turns out that 90 percent of the "very large" effects described in initial reports on medical treatments begin to shrink or vanish as more studies are done. "If taken literally, such huge effects should change everyday clinical and public health practice on the spot," Dr. John Ioannidis of the Stanford School of Medicine in California told Reuters Health by email. "Our analysis suggests it is better to wait to see if these very large effects get replicated or not." Ioannidis has made headlines before with research showing that studies in medicine are often contradicted by later evidence, a phenomenon that has been referred to as "the decline effect. "Even if they reduce the lab value, you can't be sure they reduce your risk of heart attack or stroke or fracture," [Dr. Andrew Oxman of the Norwegian Knowledge Centre for the Health Services in Oslo], who wrote an editorial about the new findings, told Reuters Health. "There are lots of examples where things start to be used and have entered the market based on surrogate outcomes and then actually proved harmful." He mentioned the heart rhythm drugs encainide and flecainide, which for many years were given to people with acute heart attacks. But then trials showed they were actually bad for these patients. "These drugs were by given well-meaning clinicians, but they actually killed more people than the Vietnam War did," Oxman said.