Adverse Drug Reaction Classification System

About ADReCS

An adverse drug reaction (ADR) is described by the World Health Organization (WHO) as a 'response to a medicine which is noxious and unintended, and which occurs at doses normally used in man.' ADRs are sometimes called side effects. Severe ADRs (SADRs) have caused significant clinical burden, and as well answer for a large portion of new drug development failure. Adverse Drug Reaction Classification System (ADReCS) is a comprehensive ADR ontology database that provides both standardization and hierarchical classification of ADR terms. The ADReCS integrates ADR and drug information collected from public medical repositories like FAERS, DailyMed, SIDER4.1, MedDRA, DrugBank, PubChem, and so on. Unique ID of four digital combinations ( is designed and assigned to each standardized ADR term, corresponding to its position in a four level tree-like architecture. At the same time, the ADReCS integrates the ADR frequency and severity corresponding to drugs from the FAERS. The database also provides tools for ADR profile comparison between drugs or rapid ADR profiling subject to chemical structure similarity.

News & Updates

2023/03  UPDATE! ADReCS has updated to version 3.2 (ADReCS v3.2). The ADR severity and frequency data based on FAERS have been updated, and the dataset of quantitative features can now be downloaded from the DOWNLOAD page.

2022/06  UPDATE! ADReCS has updated to version 3.1 (ADReCS v3.1). ADReCS has updated drug ID matching information with PubChem, DrugBank, KEGG, and MeSH.

2021/05  UPDATE! The ADR frequency and severity based on FAERS have been integrated into ADReCS.

2020/12  UPDATE! Check and optimize the data in ADReCS v3.0.

What ADReCS can do?

ADReCS will serve as a valuable resource to assist in various studies of clinical drug toxicity, including but not limited to:

  • Aids standardization and digitalization of ADRs or side effects
  • Builds the hierarchical relations between ADRs or side effects
  • Provides multi-dimensional and quantitative information of ADRs
  • Provides a big dataset of quality drug-ADR associations
  • Provides ADR-associated targets


Cai MC, Xu Q, Pan YJ, Pan W, Ji N, Li YB, Jin HJ, Liu K, Ji ZL. ADReCS: an ontology database for aiding standardization and hierarchical classification of adverse drug reaction terms. Nucleic Acids Res. 2015 Jan;43(Database issue):D907-13; PMID: 25361966.

Friendly Reminder

To get a better experience with this site, Mozilla Firefox, Internet Explorer, Google, Opera and Safari are advised!

Database Statistics