Objective : The purpose of this study was to lay the groundwork for understanding the details and scope of the legal definition of medicinal products, following the changes in the relevant laws and regulations. This will let readers properly understand the origins of the ongoing conflicts on herbal drugs and new drugs from natural products that are present in the medical field and the medical industry. Possible solutions are proposed in the end. Method : I analyzed the changes in definition of medicinal products since 1945 that have been used in relevant laws and regulations(i.e. Pharmaceutical Affairs Act) and drug approval process(i.e. New Drug Application and Investigational New Drug Application). Results : Legal definition of medicinal products has changed in accordance with the changes in the pharmaceutical industry, such as the establishment of dualistic medical and pharmaceutical System and the introduction of the substance patent. Due to those changes, boundaries of Western medicinal products and health food expanded, while those of herbal medicine products relatively downscaled. Conclusion : Legal definition of medicinal products-i.e. Herbal Drugs, Crude Drugs, and New Drugs from Natural Products-should be reestablished according to academic legitimacy and dualistic medical and pharmaceutical System.