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

2021/05  UPDATE! ADReCS has updated to version 3.1 (ADReCS v3.1). The ADR frequency and severity based on FAERS have been integrated into ADReCS v3.1.

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

2019/05 UPDATE! ADReCS has updated to version 3.0 (ADReCS v3.0). A total of 194 new drugs, 6,111 new ADRs(PT), and corresponding 466,625 new Drug-ADR pairs minded from the FDA Adverse Event Reporting System (FAERS) were included.

2018/08 UPDATE! A mirror site( is deployed for more availability and stable access.

2018/05 UPDATE! ADReCS has updated to version 2.2 (ADReCS v2.2) including 2,399 drugs, 5,160 PTs, 1,333 HLTs, 327 HLGTs and 27 SOCs. The severity grades of ADRs, ADR-related proteins and tools for ADR similarity searching and structure similarity searching have been integrated into ADReCS v2.2.

What ADReCS can do?

ADReCS will serve as a useful resource for aiding different aspects of toxicological studies, especially system toxicology and in silico drug safety evaluation. The ADReCS can be easily applied in the fields of:

  • Computational systems toxicology
  • Mechanism study of drug toxicity & Comparative drug safety evaluation
  • High throughput in silico drug safety evaluation & Drug design
  • Data mining of health information
  • Other computational toxicological applications


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

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Database Statistics

Data Type Count
ADR System Organ Class (SOC) 27
High Level Group Terms (HLGT) 330
High Level Terms (HLT) 1,448
Preferred Terms (PT) 7,570
All unique ADR terms 9,375
Drugs 2,526
Drug-ADR pairs 809,346
ADR-Protein Pairs 1,433