This research aims to determine the cause-effect series with concepts of problem events, especially drug-addiction, expressed by several simple sentences from web documents. The cause-effect series benefits for the problem-solving system. The research has two problems; how to determine sentences having cause/effect event concepts, and how to determine the cause-effect relation pairs with the boundary consideration. Therefore, we apply WordCo to solve the sentences with cause/effect event concepts. We then propose using WordCo-vector pairs to determine the cause-effect relation pairs. The research results provide the high precision of the cause-effect series determination from the documents.