Medical Dictionary for Regulatory Activities(MedDRA) is a clinically validated international medical terminology thesaurus used by regulatory authorities and the biopharmaceutical industry during the regulatory process, from pre-marketing (clinical research phase 0 to phase 3) to post-marketing activities (pharmacovigilance or clinical research phase 4), and for safety information data entry, retrieval, evaluation, and presentation. Moreover, it is the adverse event classification dictionary.
The MedDRA dictionary is organized with a five-level hierarchy. The highest or broadest level is System Organ Class (SOC), further divided into High-Level Group Terms (HLGT), High-Level Terms (HLT), Preferred Terms (PT) and finally into the most granular Lowest Level Terms (LLT). Also, the MedDRA dictionary includes Standardised MedDRA Queries (SMQs). SMQs are groupings of terms that relate to a defined medical condition or area of interest.