Executive Summary

FDA Commissioner Mark McClellan, MD/PhD, asks RAND Corp.'s Paul Shekelle, MD/PhD, if "the available evidence supports a causal relationship at a somewhat less certain level of scientific proof" than the "95% certainty" standard often used in studies, according to an April 4 email correspondence. Shekelle replies that although "95% certainty" level does not exist to link ephedra with adverse events, "we judge that it is much more likely than not that such a relationship exists" and "we are much more than 50% confident that it exists." McClellan also asks whether evidence of a causal relationship "is more certain for the special circumstances suggested in FDA's proposed warning label," such as strenuous exercise or consumption of other stimulants. Shekelle notes RAND report "did not find sufficient evidence to reach firm conclusions," but adds that does not mean the risk is not increased...