Placebo-controlled trials are held by many, including regulators at agencies like the United States Food and Drug Administration, to be the gold standard in the assessment of new medical interventions. Yet the use of placebo controls in clinical trials has been the focus of considerable controversy. In this two-part article, we challenge a number of common beliefs concerning the value of placebo controls. Part I critiques statistical and other scientific justifications for the use of placebo controls in clinical research. The (...) continued use of placebo controls in clinical trials on diseases for which accepted treatment exists raises equally important ethical, legal, and regulatory issues for which various justifications have been given. Defense of this practice relies on normative as well as empirical myths.In their attack on the prevailing use of placebo controls, Kenneth Rothman and Karin Michels emphasize that this practice stands in violation of the World Medical Association's guidelines on the ethics of human experimentation, most commonly known as the Helsinki Declaration. (shrink)