Medical coding transforms the free-text medical terms reported by investigators into standardized, structured codes that enable consistent aggregation and analysis across the trial and comparison with other studies. When investigators document adverse events, medical history, or concomitant medications in their own words, these verbatim terms must be mapped to appropriate entries in recognized medical dictionaries to facilitate regulatory review and safety signal detection. This translation requires trained coders with clinical knowledge to select the most appropriate standardized terms.

For adverse event coding, the Medical Dictionary for Regulatory Activities provides the internationally accepted standard terminology. Coders must select the Lowest Level Term or Preferred Term that most accurately represents the reported event, considering the clinical context and any clarifying information provided by the investigator. The hierarchical structure of MedDRA then enables analysis at various levels of granularity, from specific preferred terms to broader system organ class groupings. Coding conventions and guidelines help ensure consistency, but judgment is often required when verbatim terms are ambiguous or when multiple possible codes could apply.

Medication coding typically uses the WHO Drug Dictionary, which provides a standardized classification of pharmaceutical products based on their active ingredients, therapeutic classifications, and other properties. This coding enables identification of concomitant medications that might interact with the investigational product, analysis of medication use patterns in the study population, and comparison with external data sources. Quality control processes verify coding accuracy and consistency, and coding decisions are documented to support traceability and enable review of questionable assignments.