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© 2024 International Health Terminology Standards Development Organisation.  All rights reserved.  SNOMED CT® was originally created by the College of American Pathologists.

This document forms part of the SNOMED CT® MedDRA Map package distributed by International Health Terminology Standards Development Organisation, trading as SNOMED International, and is subject to the SNOMED CT® Affiliate License, details of which may be found at

No part of this document may be reproduced or transmitted in any form or by any means, or stored in any kind of retrieval system, except by an Affiliate of SNOMED International in accordance with the SNOMED CT® Affiliate License. Any modification of this document (including without limitation the removal or modification of this notice) is prohibited without the express written permission of SNOMED International.

Any copy of this document that is not obtained directly from SNOMED International [or a Member of SNOMED International] is not controlled by SNOMED International, and may have been modified and may be out of date. Any recipient of this document who has received it by other means is encouraged to obtain a copy directly from SNOMED International [or a Member of SNOMED International. Details of the Members of SNOMED International may be found at].

Access within SNOMED International member countries is provided by the Member National Release Centre in each country, via the relevant Member webpage.  Affiliates of SNOMED International in non-member countries can access the table through their MLDS (Member Licensing & Distribution Service) account.  

Page At A Glance

1. Introduction

The SNOMED CT terminology provides a common language that enables a consistent way of indexing, storing, retrieving, and aggregating clinical data across specialties and sites of care. The International Health Terminology Standards Development Organisation (IHTSDO®) maintains the SNOMED CT technical design, the content architecture, the SNOMED CT content (including the concepts table, the descriptions table, the relationships table, a history table and mappings), and related technical documentation. 

This document is intended to give a brief description, background context and explanatory notes on the SNOMED CT International/ICH (International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use) work through the EU funded WEB RADR 2 project and the resulting SNOMED CT/MedDRA maps, which were first published as a Production release from April 2021 and are now subject to annual release. This document covers the background to the collaboration between SNOMED International and ICH, through the MedDRA MSSO, as part of the project and goes on to cover the consequent release artefacts. It is not a detailed technical document of SNOMED CT, MedDRA or the SNOMED CT International/ MedDRA release. Nor does it seek to provide an editorial policy for this content though does provide a link to the Mapping conventions developed and used.

The Production releases are available to licensed users of either SNOMED CT or MedDRA.

2. Audience for this document

This document should be read by all those (SNOMED International National Release Centers, vendors of electronic health records, terminology developers, Regulators and Pharmaceutical Industry) with an interest in the usage of this content in SNOMED CT and its linkage with MedDRA i.e. the SNOMED CT to MedDRA and MedDRA to SNOMED CT maps based on a priority set of MedDRA content. 

3. Background

In 2018, SNOMED International and ICH joined the WEB-RADR 2 project, funded by Innovative Medicines Initiative (IMI). SNOMED International and ICH (through MedDRA MSSO) led the effort to develop 2 maps between SNOMED CT and MedDRA. A specific work package was devoted to this purpose and included participants from regulatory authorities and industry as well as SNOMED International and MedDRA MSSO. The project delivered the following:

  • 2 maps (MedDRA to SNOMED CT and SNOMED CT to MedDRA) of frequently-used pharmacovigilance MedDRA terms that were identified from the databases of the UK’s Medicines & Healthcare products Regulatory Agency (MHRA) and the European Medicines Agency (EMA). This subset represents the high value terms to support interoperability between the terminologies.
  • A set of Mapping conventions that were drafted as part of a pilot set and updated for the main body of work.
  • A small number of content additions to SNOMED CT in support of the MedDRA high value terms as defined by scope and editorial rules of SNOMED CT.

The Use cases of the project and the process of maintenance and updating of the 2 maps are defined as follows:

SNOMED CT to MedDRA map use case:

Key pharmacovigilance concepts when coded in SNOMED CT in an electronic health record could be converted to MedDRA for the purpose of adverse event reporting to regulatory authorities or for the purposes of epidemiological research. 

MedDRA to SNOMED CT map use case:

Clinical care decision support: Terms coded in MedDRA representing adverse events, warnings, and other regulatory information in product labeling could be converted into SNOMED CT so that the information is integrated into the electronic health record or decision support system to be visible to healthcare professionals when prescribing, dispensing, or administering the product to patients.

Map development process:

The mapping work was undertaken using dual independent review by mappers who were Consortium members of the WEB RADR 2 project and experts in either SNOMED CT or MedDRA. Quality Assurance, based on the mapping conventions specifically developed against the use cases, was managed as part of the process by SNOMED International and MedDRA MSSO (on behalf of ICH) and technical assurance reports provided weekly using the Mapping tool used by all participants.  In parallel to the mapping work, the operational aspects were developed to support the activities and processes to enable the 2 Maps to move in to Production in April 2021 and from there to be maintained and updated according to changes within the 2 terminologies and Use Case based requirements for additions to the two Maps - thus meeting one of the key requirements of IMI to produce products in the project that are sustainable over time.

In April 2020, the Alpha release of the SNOMED CT to MedDRA and MedDRA to SNOMED CT maps was made available by both SNOMED International and MedDRA MSSO (on behalf of ICH), based on the work done in the WEB RADR 2 project (which finished in June 2020). The maps were in RF2 format to support those who have SNOMED CT enabled systems, and a human readable format for other users.  All feedback received from the Alpha release was considered and where appropriate updates or revision to the maps were undertaken.

In particular it was found necessary to add new content to support the capture of data to support the COVID-19 pandemic as identified by the regulators.

4. Annual release and ongoing maintenance and updating. 

The scope of the SNOMED International and ICH work through the WEB RADR 2 project has been outlined above. SNOMED International and ICH have subsequently entered in to a Collaboration Agreement, for an initial period of 5 years to support the ongoing maintenance and updating of the 2 maps. 

Under the terms of the Collaboration agreement between SNOMED International and the ICH, the Maps will be issued annually by both SNOMED International in RF2 format and MedDRA MSSO in spreadsheet format. Documented quality assurance processes will ensure both formats are the same and supporting materials are produced jointly. In addition, criteria for extending the Maps have been agreed and managed through agreed processes to ensure that the products meet the needs of the different stakeholder groups as defined by the Use Cases. A change request system has been developed, separate to SNOMED International CRS, and is managed on a day to day basis by MedDRA MSSO. Details of the change request system, how to use it and the criteria against which decisions for change are made can be found at:

5. Release content

5.1. Overview

The MedDRA derivative content is released under a project-specific module (816211006) with component identifiers that are within the main IHTSDO (International Release) namespace. Placement in the SNOMED hierarchy is based on existing MedDRA groupings ('collective terms'). 

5.2. Content detail

The initial content of these maps, released in April 2021, was based on a high value set of MedDRA terms identified as part of the WEB RADR 2 project, taking data from European Medicines Agency and  UK’s Medicines & Healthcare products Regulatory Agency (MHRA) - just under 7500 were evaluated for being in scope of SNOMED CT. For information - approximately 100 new concepts were added to SNOMED CT as a consequence of this work. In addition, some COVID related content was added at the request of regulators.

This 2022, as well as providing updates based on changes in SNOMED CT and MedDRA, includes an additional 291 new or revised maps which have been created as a result of requests through the change request system.

5.3. Dependent Content

The January 2022 SNOMED CT International Edition is the baseline for the May 2022 SNOMED CT MedDRA Map package, and therefore all filenames and record have been assigned the value of 20220131 in the effectiveTime field. The Maps use MedDRA version 24.1, released September 2021. 

6. Obtaining the release package

Access within IHTSDO member countries is provided by the Member National Release Centre in each country, via the relevant Member page. Affiliates of IHTSDO in non-member countries can access the table through their Member Licensing and Distribution Service (MLDS) account. Please contact for more information if required. 

MedDRA users can access the spreadsheet version of the maps in the Downloads section of

Users of the Maps should have a licence for either MedDRA and SNOMED CT.

If you’re having any problems getting hold of the SNOMED CT MedDRA Simple Map Package, please contact

Additional information 

Please visit for links to:

  • Mapping Conventions (for these maps)
  • Criteria for accepting requests for changes or additions to these 2 maps
  • Links to Map Change Request tool and Map Change Request Tool guidance 

Please see the following page for the "MedDRA to SNOMED CT and SNOMED CT to MedDRA Mapping Conventions":

7. Technical Notes

7.1. RF2 package format

The RF2 package convention dictates that it contains all relevant files, regardless of whether or not there is content to be included in each particular release.  Therefore, the package contains a mixture of files which contain both header rows and content data, and also files that are intentionally left blank (including only a header record).  The reason that these files are not removed from the package is to draw a clear distinction between:

  1. ...files that have been deprecated (and therefore removed from the package completely), due to the content no longer being relevant to RF2 in this or future releases, and 
  2. ...files that just happen to contain no data in this particular release (and are therefore included in the package but left blank, with only a header record), but are still relevant to RF2, and could therefore potentially contain data in future releases.

This allows users to easily distinguish between files that have purposefully been removed or not, as otherwise if files in option 2 above were left out of the package it could be interpreted as an error, rather than an intentional lack of content in that release.

7.2. JSON file

A metadata file has been added into the MedDRA map package in order to provide additional information on the Release package.  It can be found directly in the main package, and is called "release_package_information.json".

The data included so far is mostly based around additional information on the package structure and its' contents, but also has data describing the versions of the two products being mapped, and the directionality of the two map files.

7.3. RF2 map files

Both SNOMED CT to MedDRA and MedDRA to SNOMED CT simple map files are contained in the same package, and therefore are linked by the same moduleID (816211006).

However, they can be individually identified by their relative refset ID's, as follows:

  • SNOMED CT to MedDRA = 816210007
  • MedDRA to SNOMED CT = 1193497006

An opportunity has been identified to improve the format of the SNOMED International Map Reference Set products.  This will apply to all types of simple and complex Map Reference Sets going forward, including (but not limited to) the SNOMED CT MedDRA Simple Map package, first released back in April 2021.  

The existing SNOMED CT map reference sets were originally designed for maps in the direction from SNOMED CT to another code system, manifested by the use of a ‘mapTarget’ string attribute used to represent the code in the other code system.  The new and improved map reference set patterns will be introduced with a ‘mapSource’ attribute, in order to more accurately represent maps from other code systems to SNOMED CT. 

The refined format provides users with more clarity when using maps of either direction, as well as additional map metadata representing the new refset patterns and correlation values.  Users will also benefit from clearer and more predictable naming of the map refsets, as the map reference set concepts have been reviewed and updated to follow the refined description patterns.  Please see the links below for the updated technical details including the improvements:

The first product to be improved using the new designs is the SNOMED CT MedDRA Simple Map package.  After in-depth discussions with the communities’ expert advisory bodies, the users confirmed that their preference was to retain the historical data from April 2021.  

It was therefore agreed that the May 2022 SNOMED CT MedDRA Map package will be published as follows:

  • …with all new May 2022 content in the improved format 
    • ...this required the MedDRA to SNOMED CT refsetID to change from 816209002 (old format) to 1193497006 (new format).  
    • refsetDescriptor records have also been added to the release package in order to describe this new refset.
  • …with all relevant historical MedDRA data (from April 2021) also in the new format.
  • …with the historical April 2021 map records that were in the original format inactivated (in order to retire the relevant UUID’s) - the inactivations are being published in the new package in the new format.  They will also be available in the original format in a separate package, to be requested on demand if any users require it.  
  • All of this means that the May 2022 package now appears as if the original April 2021 MedDRA release was actually published in the new format.  Therefore, the May 2022 MedDRA Release is published as a complete, consolidated package, with all original data from 2021 plus all new inactivations/changes from the latest cycle presented in the new and improved format.

If you have any questions on the improvements please let us know on with the subject "May 2022 SNOMED CT MedDRA Simple Map package format question".


Final Version






Jane MillarApproved


Monica HarryApproved


Donna MorganApproved

Download .pdf here:

Draft Amendment History







Andrew AtkinsonInitial draft


Andrew AtkinsonFinal confirmation of format and technical details, based on the new and improved format.


Donna MorganComments added 


Jane MillarFinal Updates

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