The consistent symptoms include facial flushing, vague uneasy feelings of weakness, abdominal and low back pain, nausea, vomiting, dyspnea, and chest pain. In severe reactions, these symptoms are followed within minutes by cyanosis, loss of consciousness, and hypotension, with the potential for cardio-pulmonary arrest and death. The adverse reaction to VK1 injection is believed by many to be classified as anaphylaxis. In December 2011, the State Food and Drug Administration, China, and the National Center for Adverse Drug Reaction Monitoring, China, issued a notice raising concern regarding serious anaphylaxis resulting from VK1 injection. The database in the State Food and Drug Administration contained a total of 8146 cases of adverse reactions between January 2004 and May 2011. The adverse reactions were primarily associated with the intravenous administration of VK1. The United States Pharmacopeia and the Martindale Extra Pharmacopeia have reported that VK1 can cause hypersensitization. The medical use instructions for VK1 products from Merck, US, report that VK1 can induce anaphylaxis. After reviewing the reaction description in the Food and Drug Administration SRSAR file, Louis found that the patients who experienced such a reaction were never identified as “anaphylactoid”. Although most of these episodes have been described as anaphylaxis in studies of clinical cases, the number of these reactions that were IgE-mediated is unclear. Furthermore, Yang collected 46 cases of allergicshock for vitamin K1 injection, and 19 patients were administered vitamin K1 injection for the first time. These results are contradictory to the mechanism of anaphylaxis. Some reports have classified these adverse reactions as anaphylactoid reactions. Riegert-Johnson has reported one case of an adverse reaction to VK1 and concluded that this patient most likely experienced an anaphylactoid hypersensitivity reaction. Fiore has defined “anaphylactoid” as an adverse drug event in which at least one of the reported adverse drug reactions includes any of the following CONSTART entries: anaphylaxis, allergic reaction, apnea, death, cardiac arrest, hypotension, shock or vasodilation. The attempt to identify the nature of VK1 injection-induced adverse reactions as anaphylaxis or anaphylactoid reactions has clearly been relatively unsuccessful. Paradoxically, VK1 is required in the body to participate in coagulation but can also cause anaphylaxis. On the other hand, Tween-80, a non-ionic surfactant, is the most extensively used solubilizer in lipid-soluble drugs containing VK1. Growing evidence GDC-0199 suggests that Tween-80 used as a solubilizer can induce anaphylactoid reactions. Therefore, we considered whether VK1 injection-induced adverse reactions are anaphylactoid reactions triggered by the solubilizer. The objectives of the present study were to ascertain the nature of the adverse reactions to VK1 injection. Clearly distinguishing the types of adverse reactions and determining the trigger will be significant in finding solutions to prevent and reduce the adverse reactions.