Given the high risk and lengthy procedure of traditional drug development, drug repurposing is gaining more and more attention.Although many types of drug information have been used to repurpose drugs, drug-drug interaction data, which imply possible physiological effects or targets of drugs, remain unexploited.In this work, similarity of drug interaction was employed to infer similarity of the physiological effects or targets for the drugs.We collected 10 835 drug-drug interactions concerning 1074 drugs, and for 700 of them, drug similarity scores based on drug interaction profiles were computed and rendered using a drug association network with 589 nodes (drugs) and 2375 edges (drug similarity scores).The 589 drugs were clustered into 98 groups with Markov Clustering Algorithm, most of which were significantly correlated with certain drug functions.This indicates that the network can be used to infer the physiological effects of drugs.Furthermore, we evaluated the ability of this drug association network to predict drug targets.The results show that the method is effective for 31 7 of 561 drugs that have known targets.Comparison of this method with the structure-based approach shows that they are complementary.In summary, this study demonstrates the feasibility of drug repurposing based on drug-drug interaction data.