Terfenadone is primarily used as an intermediate in the synthesis of pharmaceutical compounds, particularly in the development of antihistamines. It plays a key role in the production of active pharmaceutical ingredients that target allergic reactions by blocking histamine receptors. Due to its structural properties, it is valuable in creating metabolites and derivatives with improved pharmacokinetic profiles. It has also been used in research settings to study metabolic pathways and drug interactions, especially those involving liver enzymes like CYP3A4. Its application is mostly confined to laboratory and industrial pharmaceutical development rather than direct therapeutic use.