DrugBank 4.0 is a comprehensive database containing extensive biochemical and pharmacological information about drugs, their mechanisms, and their targets. Since its first release in 2006, DrugBank has evolved significantly, incorporating user feedback and advances in drug research. The latest version, DrugBank 4.0, includes data on drug metabolism, absorption, distribution, metabolism, excretion, and toxicity (ADMET), as well as quantitative structure-activity relationship (QSAR) information. These enhancements facilitate research in xenobiotic metabolism, pharmacokinetics, pharmacodynamics, and drug design. Over 1200 drug metabolites and 1300 drug metabolism reactions have been added, along with dozens of drug metabolism pathways. Each DrugCard now includes over 30 ADMET parameters, bringing the average number of quantitative ADMET values for FDA-approved drugs close to 40. Referential nuclear magnetic resonance (NMR) and mass spectrometry (MS) spectra have been added for almost 400 drugs, along with spectral and mass matching tools to aid compound identification. New search tools, including a simple analysis of drug-target, enzyme, and transporter associations, have been introduced to help users understand drug-drug interactions. DrugBank is a repository of drug, drug-target, and drug action information maintained by domain experts and biocurators. Its data are curated from primary literature sources, making it a referential drug data source for many databases. The database has expanded to include data on drug structures, drug salt-forms, drug names, drug targets, and drug actions. Numerous approved and experimental drugs have been added, along with new data fields describing each drug. New search tools have also been developed or improved to make information easier to find. Enhancements in DrugBank 4.0 include improvements to existing data, the addition of new data fields, new and enhanced search features, and a new user feedback/commenting system. The database now includes over 8000 duplicated or partially duplicated brand names and synonyms, which have been edited or removed. Drug classes are grouped based on therapeutic effects and mechanisms of action, with a new classification system based on the Anatomical Therapeutic Chemical (ATC) Classification System. New data fields include information on drug metabolism, ADMET, pharmacometabolomics, pharmacogenomics, and QSAR. The database also includes extensive chemical taxonomy and classification systems for compounds. DrugBank 4.0 includes a new browsing feature called Reaction Browse, which facilitates the viewing and searching of drug metabolism reactions. A new search tool called BioInteractor provides insight into drug-drug interactions by analyzing drug-target, -enzyme, and -transporter associations. The database also includes a new text search engine and Data Extractor, which allow users to search and extract data more efficiently. The database has also been enhanced to include a wide range of spectral data and tools for metabolomic studies. DrugDrugBank 4.0 is a comprehensive database containing extensive biochemical and pharmacological information about drugs, their mechanisms, and their targets. Since its first release in 2006, DrugBank has evolved significantly, incorporating user feedback and advances in drug research. The latest version, DrugBank 4.0, includes data on drug metabolism, absorption, distribution, metabolism, excretion, and toxicity (ADMET), as well as quantitative structure-activity relationship (QSAR) information. These enhancements facilitate research in xenobiotic metabolism, pharmacokinetics, pharmacodynamics, and drug design. Over 1200 drug metabolites and 1300 drug metabolism reactions have been added, along with dozens of drug metabolism pathways. Each DrugCard now includes over 30 ADMET parameters, bringing the average number of quantitative ADMET values for FDA-approved drugs close to 40. Referential nuclear magnetic resonance (NMR) and mass spectrometry (MS) spectra have been added for almost 400 drugs, along with spectral and mass matching tools to aid compound identification. New search tools, including a simple analysis of drug-target, enzyme, and transporter associations, have been introduced to help users understand drug-drug interactions. DrugBank is a repository of drug, drug-target, and drug action information maintained by domain experts and biocurators. Its data are curated from primary literature sources, making it a referential drug data source for many databases. The database has expanded to include data on drug structures, drug salt-forms, drug names, drug targets, and drug actions. Numerous approved and experimental drugs have been added, along with new data fields describing each drug. New search tools have also been developed or improved to make information easier to find. Enhancements in DrugBank 4.0 include improvements to existing data, the addition of new data fields, new and enhanced search features, and a new user feedback/commenting system. The database now includes over 8000 duplicated or partially duplicated brand names and synonyms, which have been edited or removed. Drug classes are grouped based on therapeutic effects and mechanisms of action, with a new classification system based on the Anatomical Therapeutic Chemical (ATC) Classification System. New data fields include information on drug metabolism, ADMET, pharmacometabolomics, pharmacogenomics, and QSAR. The database also includes extensive chemical taxonomy and classification systems for compounds. DrugBank 4.0 includes a new browsing feature called Reaction Browse, which facilitates the viewing and searching of drug metabolism reactions. A new search tool called BioInteractor provides insight into drug-drug interactions by analyzing drug-target, -enzyme, and -transporter associations. The database also includes a new text search engine and Data Extractor, which allow users to search and extract data more efficiently. The database has also been enhanced to include a wide range of spectral data and tools for metabolomic studies. Drug