Most drugs contain pharmaceutical excipients. These are pharmacologically inactive substances used as vehicles for the active ingredients of a medication. Some of these pharmaceutical excipients are produced from allergenic foods (e.g., milk, egg, peanut, soybean, and sesame) and removing proteins completely from such excipients is difficult. Therefore, if individuals with food allergy consume drugs containing allergenic food-derived excipients, eliminating the risk of developing specific allergic symptoms induced by them may not be possible. We determined the levels of proteins in pharmaceutical excipients and ethical drugs (inhalants and injections) by spectrophotometric analyses. The level of protein in the pharmaceutical excipient lactose in each sample was approximately 1 mg/g. In the case of oils from soybeans, peanuts, and sesame in pharmaceutical excipients, proteins were detected in the range 7-9 microg/g sample. We also determined levels of allergenic proteins in pharmaceutical excipients and ethical drugs using commercial enzyme-linked immunosorbent assay systems. The milk proteins in lactose were detected in the range 1.39-13.07 microg/g. The results of this study suggest that physicians, patients with food allergies, pharmacists, and healthcare providers must pay attention to presence of potential impurities those may cause allergic symptoms in pharmaceutical products.