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MedDRA or Medical Dictionary for Regulatory Activities is a clinically validated international medical terminology dictionary (and thesaurus) used by regulatory authorities in the pharmaceutical industry during the regulatory process, from pre-marketing to post-marketing activities, and for data entry, retrieval, evaluation, and presentation. In addition, it is the adverse event classification dictionary endorsed by the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH).
Originally available in English and Japanese, MedDRA is now also translated into Chinese, Czech, Dutch, French, German, Hungarian, Italian, Portuguese and Spanish.  MedDRA is widely used internationally, including in the United States, European Union, and Japan. Its use is currently mandated in Europe and Japan for safety reporting.
Organization of the dictionary
The MedDRA dictionary is organized by System Organ Class (SOC), divided into High-Level Group Terms (HLGT), High-Level Terms (HLT), Preferred Terms (PT) and finally into Lowest Level Terms (LLT). In addition, the MedDRA dictionary includes Standardized MedDRA Queries (SMQs). SMQs are groupings of terms that relate to a defined medical condition or area of interest.
Individual cases are usually coded for data entry at the most specific (LLT) level, and outputs of counts or cases are usually provided at the PT level. The higher levels (HLT, HLGT and SOC) as well as SMQ are used for searching and for organisation and subtotalling of outputs.
Maintenance of MedDRA
MedDRA is managed by the MSSO (Maintenance and Support Services Organization). The International Federation of Pharmaceutical Manufacturers and Associations (IFPMA) is the Trustee of the International Conference on Harmonisation (ICH) Steering Committee and holds the intellectual property rights (ownership) of MedDRA. The ICH has contracted Northrop Grumman to act as the MSSO. MedDRA is free for regulators and priced according to company revenue for industry. The Japanese counterpart for MSSO is called JMO. 
The MSSO updates MedDRA according to subscriber change requests, for example to add a new medical concept that is yet to be in MedDRA or to change an existing concept. The decisions are made by international medical officers on how to map the terminology within the grouping categories according to a general consensus based on language considerations internationally.
The MSSO releases updated MedDRA versions twice a year - in March and September. The March release is the main annual release and contains changes at the HLT level and above along with LLT and PT changes. The September release typically contains changes only at the LLT and PT level. The September 2015 Version 18.1 release is the current version.
- "Welcome to MedDRA".
- "What are the structural elements of the terminology in MedDRA?". MedDRA FAQ. Retrieved 25 January 2012.
- "About MSSO".