Definition · Plain-language
MedDRA
MedDRA, the Medical Dictionary for Regulatory Activities, is the standardised international medical terminology used to code symptoms, diagnoses, indications and adverse events for regulatory reporting.
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What MedDRA is for
MedDRA is a clinically validated, standardised medical terminology developed under the auspices of the International Council for Harmonisation (ICH). Its purpose is to give regulators and the pharmaceutical industry a single, shared vocabulary for recording and communicating medical information about medicines throughout their life cycle — from clinical trials to post-marketing safety. By coding free-text descriptions to standard terms, MedDRA allows adverse-event and other data to be aggregated, queried and compared consistently, even when the original reports use different wording or languages.
The MedDRA hierarchy
MedDRA terms are organised in a five-level hierarchy. At the broadest level sit System Organ Classes (SOC), grouping by aetiology, body system or purpose. Beneath these are High Level Group Terms (HLGT) and High Level Terms (HLT), which provide intermediate groupings. The Preferred Term (PT) is the level most used for analysis, representing a single medical concept. The most granular level is the Lowest Level Term (LLT), which captures the specific way information was reported and maps up to a Preferred Term. This structure supports both detailed coding and higher-level aggregation.
How it is used in practice
MedDRA underpins the coding of adverse events in pharmacovigilance databases such as FAERS and EudraVigilance and the reporting of safety data in regulatory submissions. Standardised MedDRA Queries (SMQs) group related Preferred Terms to help retrieve cases relevant to a particular medical condition during signal detection and analysis. Consistent application of the terminology is essential: how an event is coded affects how it is grouped, counted and detected, so coding conventions and dictionary versioning are managed carefully.
Key facts
At a glance
- Definition: Standardised international medical terminology for regulatory reporting.
- Stands for: Medical Dictionary for Regulatory Activities.
- Developed under: International Council for Harmonisation (ICH).
- Hierarchy: SOC → HLGT → HLT → PT → LLT (five levels).
- Used for: Coding adverse events, symptoms, diagnoses, indications, procedures.
- Aids analysis: Standardised MedDRA Queries (SMQs) group related terms.
Common misconceptions
What people often get wrong
Often heard: MedDRA is only used for coding adverse events.
Actually: MedDRA codes a wide range of medical information — symptoms, diagnoses, indications, medical and surgical procedures and more — not just adverse events.
Often heard: The Preferred Term is the most detailed level in MedDRA.
Actually: The Lowest Level Term (LLT) is the most granular level; it maps up to a Preferred Term, which is the level commonly used for analysis.
Often heard: MedDRA terminology is fixed and never changes.
Actually: MedDRA is updated on a regular release schedule, so version control matters when coding and comparing data across time.
Going deeper
