Declared Inactive Ingredients in US Oral Drug Listings: A Reproducible Census of Prevalence, Labeling Coverage, and Within-Name Variation.

Background A current assessment of structured drug labeling can update excipient-declaration prevalence, quantify structured-data coverage, and describe variation among listings sharing a prescription generic name. Building on prior formulation-level analyses, this study contributes a current, fully reproducible public-data snapshot with pharmacologic-class-resolved declaration patterns and a within-generic-name declaration-consistency analysis. Methods We conducted a cross-sectional analysis of a published census derived from the openFDA National Drug Code (NDC) Directory export dated 2026-07-18 and DailyMed Structured Product Labeling (SPL). The analytic denominator comprised 50,005 distinct oral Product NDC listings with an exact SPL product match and at least one structured inactive-ingredient (IACT) declaration. We described listing-level excipient burden and prevalence, unique qualitative excipient profiles, structured-declaration availability, and patterns across dosage forms, marketing categories, and Established Pharmacologic Classes (EPCs). A predefined Unique Ingredient Identifier (UNII)-based panel identified selected avoidance-relevant excipients. Among prescription generic-name groups with at least two listings, we identified affected groups in which every observed listing declared the target. Results Listings declared a median of nine excipients (interquartile range {IQR}, 6-12; maximum, 41). Magnesium stearate (68.07%), titanium dioxide (53.27%), and microcrystalline cellulose (52.88%) were most prevalent. The 50,005 listings contained 13,540 unique qualitative declared excipient profiles, a mean of 3.69 listings per profile. Among exact SPL product matches, 97.99% contained at least one structured IACT declaration. Lactose was declared in 39.34% of listings, gelatin in 18.5%, and at least one panel-defined synthetic color additive in 39.96%. Within affected prescription generic-name groups, every observed listing declared lactose in 306 of 657 groups (46.58%) and gelatin in 150 of 322 groups (46.58%). Conclusions Declared excipients were common and varied across product and pharmacologic-class strata. Many listings shared the same qualitative excipient profile, although profile identity does not establish formulation identity. In some prescription generic-name groups, every observed listing declared an avoidance target. These findings describe structured declarations rather than actual composition, dispensing exposure, or therapeutic interchangeability.