Getting the wrong answer to drug-related questions could be life threatening. We need to better understand which drug-related information sources, including those on the Internet, are best for answering these questions. This paper presents data from documented information search and retrieval efforts performed under the supervision of a pharmacist, seeking answers to drug-related questions. This study uses media richness theory to inform hypotheses about information source uses. The hypotheses center on the premise that reducing uncertainty is the key to compiling a complete and accurate answer; information sources are judged based on their actual performance in supplying the answers to questions submitted to a professional drug information center. The findings of this exploratory study based on logistical and OLS regressions suggest the type of question being asked significantly influences an expert pharmacist's decision not to consult certain information sources. The findings further suggest that, depending on the type of question being asked, certain sources are much less useful than others in helping arrive at a complete answer. If pharmacists and other health professionals know what influences the sources that experts consult and which sources are the most useful, their ability to get answers to questions is likely to improve, which in turn will improve the quality of care they provide to patients. These findings have implications for theory and practice.