An excipient is any substance included in a medicinal formulation other than the active pharmaceutical ingredient (API). Excipients are classified as "inactive" in the pharmacological sense, yet each serves one or more defined functional roles that determine a product's physical stability, manufacturability, delivery profile, and patient acceptability. The Therapeutic Goods Administration (TGA) requires that all excipients in a listed or registered medicine be identified, and their functions justified, as part of the product's chemistry, manufacturing and controls (CMC) documentation.
Recognised excipient functions include: binders (hold compressed tablets together), disintegrants (promote tablet break-up in gastrointestinal fluid), fillers/diluents (provide bulk to low-dose formulations), lubricants (reduce friction during tablet compression), preservatives (inhibit microbial growth in liquid or semi-solid products), solubilisers and surfactants (improve aqueous solubility of poorly soluble APIs), stabilisers (protect against chemical or physical degradation), and colouring and flavouring agents (aid identification and palatability). A single excipient may simultaneously fulfil more than one function depending on concentration and formulation context.
In botanical and plant-based medicine formulations , including cannabinoid-containing preparations assessed by the TGA , excipient selection carries regulatory weight. Carrier oils, emulsifiers, and co-solvents used in oral liquid or sublingual dosage forms must each have their function declared and must appear on the TGA's permitted excipients lists or be individually justified under the relevant guidelines. The Australian Regulatory Guidelines for Prescription Medicines (ARGPM) and the corresponding guidelines for complementary medicines both specify acceptable excipient categories and any concentration limits.
The term "excipient function" should not be conflated with therapeutic function. Regulatory and pharmacopoeial frameworks, including the International Pharmaceutical Excipients Council (IPEC) Good Manufacturing Practices guide and the current edition of the British Pharmacopoeia (as adopted by reference in Australian practice), treat excipients strictly as functional formulation components, not as contributors to clinical effect. Classification by function also underpins post-market safety monitoring: where an excipient is associated with an adverse reaction (e.g. polyethylene glycol-related hypersensitivity), regulators can trace it through its declared functional role in the product dossier.
Sources:
- Australian Regulatory Guidelines for Prescription Medicines (ARGPM) , Therapeutic Goods Administration (TGA)
- Pharmaceutical Excipients: Background and Characterisation; StatPearls / NCBI Bookshelf
- WHO Technical Report Series No. 929: Annex 5, Guidelines on Packaging for Pharmaceutical Products (with excipient classification reference), World Health Organization