MedDRA, the Medical Dictionary for Regulatory Activities, is a clinically validated international terminology used by regulatory authorities and the biopharmaceutical industry for the standardized coding of adverse event information. It provides a structured, hierarchical framework for classifying symptoms, signs, diseases, and diagnoses reported during clinical trials and post-marketing surveillance.
Glossary
MedDRA
The Medical Dictionary for Regulatory Activities (MedDRA) is a clinically validated international terminology used by regulatory authorities and the biopharmaceutical industry for the standardized coding of adverse event information throughout the regulatory lifecycle.
MEDICAL DICTIONARY FOR REGULATORY ACTIVITIES
What is MedDRA?
The foundational international terminology for standardizing adverse event reporting and drug safety data throughout the regulatory lifecycle.
Developed under the auspices of the International Council for Harmonisation (ICH), MedDRA organizes terms into five hierarchical levels: System Organ Class, High-Level Group Term, High-Level Term, Preferred Term, and Lowest Level Term. This granular structure enables precise data entry and flexible retrieval for signal detection and aggregate safety analysis.
STRUCTURE & APPLICATION
Key Features of MedDRA
The Medical Dictionary for Regulatory Activities (MedDRA) is a clinically validated international terminology used by regulatory authorities and the biopharmaceutical industry for the standardized coding of adverse event information throughout the regulatory lifecycle.
01
Five-Level Hierarchical Structure
MedDRA organizes terminology into a five-level hierarchy providing granularity for data entry and flexibility for data retrieval:
- System Organ Class (SOC): Highest level, grouping by etiology, manifestation site, or purpose (e.g., Cardiac disorders).
- High Level Group Terms (HLGT): Sub-categories within an SOC (e.g., Coronary artery disorders).
- High Level Terms (HLT): Groupings of related PTs (e.g., Ischaemic coronary artery disorders).
- Preferred Terms (PT): The standard term for a distinct medical concept, used for international case reporting (e.g., Myocardial infarction).
- Lowest Level Terms (LLT): The most granular level, including synonyms, lexical variants, and regional dialects, mapping to a single PT.
5
Hierarchy Levels
80k+
Total Terms
02
Multi-Axiality and Primary SOC
MedDRA is multi-axial, meaning a single Preferred Term (PT) can logically belong to more than one System Organ Class (SOC). This allows a term to be retrieved and analyzed from different clinical perspectives. For example, the PT 'Headache' is linked to both the 'Nervous system disorders' SOC and the 'General disorders and administration site conditions' SOC. To prevent double-counting in statistical outputs, each PT is assigned a single Primary SOC, which is the default assignment for cumulative data presentations.
1
Primary SOC per PT
03
Standardised MedDRA Queries (SMQs)
SMQs are pre-defined, validated groupings of MedDRA terms used to support signal detection and case retrieval. They are designed to identify cases potentially related to a specific medical condition or syndrome, such as 'Anaphylactic reaction' or 'Acute pancreatitis'. SMQs can be broad (high sensitivity, capturing all possible cases) or narrow (high specificity, capturing highly likely cases), allowing safety reviewers to adjust the scope of their analysis. Each SMQ is maintained and versioned alongside the MedDRA dictionary.
100+
Production SMQs
04
Bi-Annual Versioning Cycle
MedDRA is a dynamic terminology updated twice yearly, in March and September, to reflect the evolution of medical knowledge and regulatory needs. Each update includes the addition of new terms, modification of existing terms, and the deactivation of obsolete concepts. A term is never deleted; it is marked as 'non-current' to maintain historical data integrity. Strict version control is critical for pharmacovigilance, as Individual Case Safety Reports (ICSRs) must be coded and analyzed against the specific MedDRA version in effect at the time of data lock.
2
Releases per Year
05
MedDRA Codes and Linguistic Variants
Every MedDRA term is assigned a unique, non-expressive 8-digit numeric code that remains constant across all translations and versions. This code, not the text string, is the primary key for database storage and electronic exchange. MedDRA is officially translated into multiple languages, including Japanese, Chinese, and Spanish, with each translation undergoing rigorous medical review to ensure conceptual equivalence. This allows for the global aggregation of safety data coded in local languages while maintaining analytical consistency.
8-digit
Numeric Code
06
Regulatory Mandate and Scope
MedDRA is the required terminology for electronic submissions to major regulatory authorities, including the FDA (via FAERS) and the EMA (via EudraVigilance). Its scope extends beyond adverse events to encompass medical history, indications, investigations, and social circumstances. This broad scope allows for a unified coding system across the entire clinical data lifecycle, from clinical trials to post-marketing surveillance, facilitating integrated benefit-risk assessments in documents like the Periodic Benefit-Risk Evaluation Report (PBRER).
ICH
Governing Body
MEDDRA ESSENTIALS
Frequently Asked Questions
Clear, technically precise answers to the most common questions about the Medical Dictionary for Regulatory Activities and its role in pharmacovigilance.
MedDRA, the Medical Dictionary for Regulatory Activities, is a clinically validated international terminology used by regulatory authorities and the biopharmaceutical industry for the standardized coding of adverse event information throughout the regulatory lifecycle. It works by providing a hierarchical structure of terms organized into five levels: System Organ Class (SOC) , High Level Group Term (HLGT) , High Level Term (HLT) , Preferred Term (PT) , and Lowest Level Term (LLT) . Each LLT maps to a single PT, ensuring that synonymous or lexically variant descriptions of the same medical concept are aggregated for consistent signal detection and aggregate reporting. The terminology is maintained by the Maintenance and Support Services Organization (MSSO) and undergoes bi-annual updates to reflect evolving medical knowledge.
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About the author
Prasad Kumkar
CEO & MD, Inference Systems
Prasad Kumkar is the CEO & MD of Inference Systems and writes about AI systems architecture, LLM infrastructure, model serving, evaluation, and production deployment. Over 5+ years, he has worked across computer vision models, L5 autonomous vehicle systems, and LLM research, with a focus on taking complex AI ideas into real-world engineering systems.
His work and writing cover AI systems, large language models, AI agents, multimodal systems, autonomous systems, inference optimization, RAG, evaluation, and production AI engineering.
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