The 20th century is the period with dramatic increase in drug research and development. However, the occurrence of adverse
drug events ( ADR ) is becoming worse and worse. It was estimated that the death rate caused by ADR is on the top of the ten leading reasons, and ranks the fifth reason for the death of hospitalized patients. Many elements may limit the experiment research of new drugs before marketing, e.g., short of time, limited observation objects and case number, narrow end - points, etc. Such serious status makes it difficult to predict those rare ADRs and to warn in advance. Those drugs withdrawn after marketing in the past 20 years were analyzed here regarding their causes and risks. It suggested here that the clinical trials pre- marketing and the auto- reporting system of ADR should be strengthened. It emphasized the necessity of clinical observations and medical records for those post - marketing new drugs. It also emphasized the importance to set up a post - marketing drug surveillance system and to build the database of pharrnaco- epidemicology. Health care providers play major roles in the prevention of ADR.