Meaning of 'Excipients'
The ingredients of medicines are often divided into Active Pharmaceutical Ingredients (API) and excipients. Put simply, excipients are all the ingredients other than the active pharmaceutical ingredient!
But it is important to realise that while a particular substance might be the API in one product (such as dextrose in an infusion), the same substance could well be used as an excipient in many other products (such as Armour Thyroid).
I love the word excipients.
Functions of Excipients
Excipients perform a wide range of functions. Some of these are most important in the manufacturing process, some in the final product.
The formulation of products involves considering not just the API and the excipients individually, but how they all work together.
Functions of excipients include:
- Antiadherents
- Antioxidants
- Binders
- Buffering agents
- Bulking agents
- Coating agents
- Colouring agents
- Diluents
- Disintegrants
- Emulsifiers
- File formers
- Flavouring agents
- Gelling agents
- Glidants
- Humectants
- Lubricants
- Preservatives
- Release modifiers
- Sequestering agents
- Sorbents
- Suspending agents
- Sweeteners
- Vehicles
- Viscosity agents
- Wetting agents
Some excipients have multiple functions. For example, croscarmellose puffs up when it gets wet. This gives it an important role as a disintegrant. But it also contributes to the bulk.
Fillers
The word filler is often used in a way that seems to imply the substance is being used instead of the active ingredient - to reduce the amount of active ingredient. This is clearly not the case as the amount of Active Pharmaceutical Ingredients is defined in the product licence and is always shown. And the least expensive generic will have exactly the same amount of API as the most expensive branded version (for a given dosage).
Not quite so inactive
And we'd better remember that some of these excipients are absolutely essential.
For example:
- gastric-resistant coatings that protect the API from the effects of stomach acid.
- sodium chloride used for injections to ensure that they have the same concentration as our blood (tonicity agents).
- acidic/alkaline substances to ensure the optimum pH of the final product.
Indeed, the interactions of API and excipients are increasingly being understood and even positively exploited.
Even when an excipient is not intended to impact the person taking a medicine, it might do so. For example, when Merck changed their Euthryox levothyroxine tablets (and the same product under many other names) from using lactose to mannitol, it changed the absorption profile - being both faster and better absorbed. (Though the actual absorption would still vary across individuals.) Thus requiring re-testing and possible dose adjustments.
Allergies and Intolerances
Most approved excipients tend to be very highly purified. This usually avoids surprise issues of allergy and intolerance.
Certain excipients are known to cause problems in some people. Examples include lactose, acacia, peanut and derivatives, lanolin and derivatives.
Most medicines that contain lactose now express the amount of lactose in each dosage. And, for many, this will be a low enough quantity not to cause lactose intolerance issues.
In the UK few medicines contain any wheat ingredients. And of the few that do, this is made very clear in the list of ingredients. Even of them, fewer still are considered unsuitable for coeliacs as the wheat ingredient is almost entirely pure starch. Nonetheless, most coeliacs would probably want to avoid any product which lists wheat.
There is still the issue that it is not always easy to identify whether an ingredient is acceptable.
For example, much vitamin D3 (the API) is derived from sheep lanolin. And many ingredients can be derived from maize (corn), potatoes or other sources.
Details of excipients have not always been readily found.
Unique Ingredient Identifier (UNII)
The Unique Ingredient Identifier is an alphanumeric identifier linked to a substance's molecular structure or descriptive information and is generated by the Global Substance Registration System of the USA's Food and Drug Administration (FDA).
The USA's FDA has set up a register of excipients (and it is in cooperation with the EU's EMA and intended to be available worldwide).
Each excipient has a unique UNII number - which you will see on USA medicine documentation.
 |
| The excipients of Armour Thyroid as shown on the FDA's DailyMed site |
The top level search starts here:
https://precision.fda.gov/uniisearch
This is a link to the European Medicine Agency's guidance on excipient labelling.
Thyroid Hormones and Excipients
The doses of levothyroxine and liothyronine are minute. The amount in a tablet (whether levothyroxine or liothyronine) being around the same quantity as a single crystal of ordinary sugar. Maybe something like one thousandth of a tablet is actual thyroid hormone. (This is just to give an impression. The details will vary from one product to another.)
It is impossible to make thyroid hormone tablets that are not mostly excipient.
helvella - Excipients
Details of excipients are in my Excipients document. This includes all excipients identified in UK-licensed thyroid hormone medicines.
If the last updated date of a copy your have downloaded isn’t very recent, please download a new copy!
If you wish to link to this page on HealthUnlocked, copy the entire dark red text below and paste into a post or reply.
[i][b]helvella - Excipients[/b]
A brief discussion about the 'excipients' - the word and what they are and do.
Direct link to PDF:
https://www.dropbox.com/scl/fi/tud6r8f51au0g4w10xqa0/helvella-Excipients.pdf?rlkey=aeo2dyb635chtf30lcsiyyqj2&st=oofsriqf&dl=1
Last updated 10/02/2025[/i]
Link to blog:
https://helvella.blogspot.com/p/helvella-excipients.html
If you find anything incorrect, misleading, typos, links that don’t work, etc., please let me know. Go to my profile and use the contact details there.
