MedDRA
What does it mean in plain English?
MedDRA (Medical Dictionary for Regulatory Activities) is the standardized vocabulary that everyone in pharmacovigilance (companies, regulators, hospitals) uses to describe adverse events, symptoms, and diagnoses the exact same way. Without it, one doctor's "felt dizzy" and another's "lightheadedness" could end up counted as two separate things instead of the same signal.
It's organized as a five-level hierarchy, from broad body-system categories down to the precise wording a reporter actually used. Cases get coded at the most specific standardized level, which is what actually gets counted, compared, and analyzed, including in techniques like disproportionality analysis.
Follow one symptom down the funnel
A patient says "I felt sick to my stomach and threw up." Hover each level to see where that lands as it moves through MedDRA's five levels, broadest to most specific.
Hover a level to see its exampleGastrointestinal disorders: the broadest bucket, one of 27 top-level body-system categories.
Gastrointestinal signs and symptoms: a themed cluster within that body system.
Nausea and vomiting symptoms: a tighter grouping of closely related concepts.
Nausea: the standardized term actually used for coding, counting, and reporting.
"Felt sick to my stomach": the patient's own words, mapped onto the Preferred Term above.
It's not static. MedDRA is maintained by the MSSO and updated twice a year, with new terms added as medicine, and the way people describe their symptoms, keeps evolving.
Common Misconceptions
"Wait, isn't this basically the same as ICD, the diagnosis code my doctor already uses? Why do we need a whole separate system?"
Different job entirely. ICD (International Classification of Diseases, the World Health Organization's system for classifying diagnoses) is built for billing and public health statistics. MedDRA is built specifically to code adverse events and symptoms consistently across clinical trials and post-marketing safety data: far more granular, and purpose-built for pharmacovigilance.
