In studying the patent medicine industry in colonial Korea (1910–1945), I pay attention to the inordinately large number of peddlers and small retailers—45,688 in 1935—who functioned as human intermediaries in the burgeoning medicinal market. By almost exclusively studying printed advertisements, previous scholars have depicted the patent medicine industry as the vanguard of modern marketing or as a willing partner in the commercial propagation of the hegemonic vision of the colonial biopower. Conscious of the severely limited reach of modern media in the colonial context, I argue instead that incentivized sales intermediaries were equally significant in the success of the patent medicine industry. But the significance and contributions of the peddlers to the patent medicine industry were double-edged—the peddlers helped the industry by facilitating physical dissemination of patent medicine to end consumers, but their constant use of deception and fraud tainted the reputation of the industry. The anticipated move toward stricter regulation, however, did not happen due to two interrelated factors—a nascent group of pharmacists trained in modern pharmacology had strong ties to the patent medicine industry and the lukewarm response from the colonial government put the brakes on any meaningful reform. Overall, by bringing to the fore the pivotal roles peddlers played, my article provides a more nuanced discussion of the marketing practices of the patent medicine industry, the nature of the emerging professional class of pharmacists, and the efficacy (or lack thereof) of the regulatory power of the colonial government.