Excipients: the inactive ingredients in every medicine

When you take a tablet or swallow a syrup, you might assume the entire product consists purely of the medicine. In reality, medicines almost always contain two distinct components: the active pharmaceutical ingredient (API), which is the chemical responsible for the intended therapeutic effect, and the excipients. Excipients are the inactive ingredients, sometimes referred to broadly as binders, fillers, or coatings, that make up the physical bulk of the final product. While they do not treat the condition themselves, excipients are absolutely essential. Without them, it would be virtually impossible to manufacture, store, and safely deliver an active ingredient into the body in a reliable way.

The many roles of inactive ingredients

Excipients serve a wide variety of functions that are critical to the manufacturing and performance of a medicine. Binders hold the ingredients together in a tablet, ensuring it does not crumble, while fillers provide the necessary bulk so that a tiny amount of active ingredient can be formed into a tablet large enough to handle. Lubricants prevent the medicine from sticking to manufacturing equipment, and disintegrants help the tablet break apart in the stomach or intestine so the active ingredient can be absorbed.

In liquid medicines, preservatives are used to prevent the growth of bacteria and mould over the shelf life, while flavourings and sweeteners mask the often bitter taste of the active chemicals. Coatings might be used to protect the medicine from light or moisture, or to control the rate at which the drug is released into the bloodstream over time. Essentially, excipients transform a pure chemical compound into a stable, usable medicine.

Why generics have different excipients

A generic medicine contains the exact same active pharmaceutical ingredient as the original brand-name product, but it frequently contains different excipients. The patent on an active ingredient eventually expires, allowing other manufacturers to produce it. However, the specific formulation—the exact blend of excipients used by the original manufacturer—may still be protected by separate patents. Furthermore, different manufacturers rely on their own proprietary manufacturing processes, supply chains, and cost considerations when designing a product.

Because excipients can subtly influence how a medicine behaves in the body, regulators require generic medicines to demonstrate bioequivalence. This means the generic must deliver the active ingredient into the bloodstream at the same rate and to the same extent as the original product. As long as the generic achieves this standard, differences in excipients generally do not alter the therapeutic effect. However, these differing excipient profiles are why some people notice a slight variation in the taste, texture, or appearance of a generic compared to a brand-name medicine.

Excipients, allergies, and sensitivities

Although excipients are inactive in terms of treating disease, they are not always biologically inert. Some individuals have allergies or intolerances to specific inactive ingredients. For example, tablets frequently contain lactose as a filler, which can cause gastrointestinal discomfort for people with severe lactose intolerance. Some liquid formulations contain alcohol, while others may use colourants, such as tartrazine, which can trigger hypersensitivity reactions in a small subset of the population. People with coeliac disease may also need to be mindful of starches derived from wheat.

Because of these potential sensitivities, regulators generally require that both the active ingredients and known excipients be listed on the packaging or in the patient information leaflet. If a patient has a known sensitivity, they can check these lists before taking a new medicine. Pharmacists also play a key role in helping patients identify suitable alternatives when an excipient poses a problem.

How excipients are regulated

Excipients are not regulated as strictly as active pharmaceutical ingredients, but they are still subject to rigorous safety and quality standards. Regulatory bodies rely on established standards, such as pharmacopoeias, which are official reference books detailing the acceptable purity and quality of substances used in medicines. An excipient must be deemed safe for human consumption at the levels used in the final product. Importantly, an excipient that is safe for oral use might not be safe for injection; therefore, regulators evaluate excipients in the context of the specific medicine and its route of administration.

In South Africa, the South African Health Products Regulatory Authority (SAHPRA) evaluates the safety of the entire formulation, not just the active drug. Patients and healthcare providers can use HealthSA to look up the registration details of medicines, ensuring they are reviewing products that have passed these rigorous formulation checks. If a manufacturer wishes to use a novel excipient—one that has never been used in a registered medicine before—they must provide extensive toxicological safety data, similar to what is required for a new active ingredient.