Under Food and Drug Administration (FDA) policy, communications by prescription drug manufacturers must be backed by “substantial evidence” from “adequate and well-controlled investigations.” But numerous exceptions permit manufacturer promotion based on data other than randomized trials. The observational research presented in the Hemikrane hypothetical case in this month’s Health Affairs is methodologically flawed and also does not meet any of these exceptions. Therefore, plausible scientific and policy rationales support rules restricting the company’s communication of its findings. The FDA’s current reluctance to authorize promotional claims based on observational research is understandable. Further work is required to define the characteristics of high-quality observational research. However, as this field matures, higher-quality observational studies could meet the legal standard of an “adequate and well-controlled investigation.” At that point, the FDA will need to issue formal guidance to minimize confusion on what kinds of observational research can meet its evidentiary standards.