Hidden Ingredients (excipients) in Supplements for Dogs

Supplement manufacturers heavily promote the active ingredients in their supplements but rarely highlight their inactive ingredients and, unfortunately, seem not to spend much time thinking about them.  But, they should, as the “inactive” ingredients lurking at the bottom of a supplement label may be negatively impacting your pet’s health.

In this post, we will let you know why hidden ingredients are added to supplements and which ones may be harmful to your pet, especially if they are suffering from Cushing’s syndrome, diabetes-spectrum condition or another health condition.

What do they mean by “excipients” exactly?

Excipients are substances that are used in supplements alongside the advertised (or “active”) ingredients. Here are some different types of excipients that may be included in your pet’s supplements:

  • Binders (to stabilize the main ingredients)
  • Lubricants (to facilitate flow of the main ingredients into capsules or tablet pressing machines)
  • Disintegrates (to cause the active ingredients to dissolve quickly upon entry into the body)
  • Fillers (to occupy otherwise empty space in the capsule or tablet)
  • Flavorings
  • Coating agents, emulsifiers and preservatives (to extend shelf-life and stabilize active ingredients)
  • Coloring agents

As you can see, some types of excipients are necessary for the manufacturing, shelf life or usefulness of your supplements, while others are not.  Thus, in thinking about the excipients in your pet’s supplements, the goal is to minimize the non-essential excipients, choose the best of the essential excipients and altogether avoid the harmful ones.  Below we discuss these goals in the context of some commonly used excipients and your pet’s health.

Researching Excipients

In researching the harmful excipients that we aren’t able to cover below, there are some useful internet sources.  A good source for checking the safety of a particular binder or other excipient is the WebMD supplements database.  Unfortunately, that database doesn’t cover every possible excipient and there aren’t a lot of other easily accessible sources.  The FDA’s GRAS notices database is another source, but that database can be difficult to search and highly technical as well as potentially biased since those notices are filed by manufacturers of the noticed products.  If your dog is currently on any prescribed medications, you should check with your veterinarian and/or pharmacist to make sure there are no interactions with the excipients in your dog’s supplements.

Food-based excipients

Among the most common excipients are food-based excipients such as cellulose, rice powder and other flours, both to add essential lubrication and to fill otherwise empty space inside the capsules or tablets.


Cellulose or microcrystalline cellulose (MCC) serves as a filler and a lubricant in different dog foods and supplements. MCC is safe for all animal species, and as an added bonus, in dogs (and other “companion animals”) it is completely indigestible as dogs do not have the enzyme (cellulase) necessary for its breakdown. Thus, MCC passes through the dog with no nutritional effect.  This is ideal for dogs that may suffer from Cushing’s syndrome and/or insulin resistance as the diet for these dogs must be carefully controlled to avoid, in particular, starches, sugars and other non-structural carbohydrates.

Rice powders, flours and starches

Unlike MCC, corn starch, rice powder and other starches and flours are digestible by dogs and, although completely safe in healthy dogs, are among the worst ingredients for pets with Cushing’s syndrome, insulin resistance or other diabetes-spectrum conditions as they are simple carbohydrates.  Insulin resistance and other diabetes-spectrum conditions are common co-conditions with Cushing’s syndrome.  As such, these simple carbohydrates may contribute to your dog’s condition.  Moreover, even in healthy dogs, they can feed unhealthy gut bacteria and, thereby, worsen overall health.  (Worse still, if your dog is being treated with lignans, a dysregulated gut microflora may make the treatment less effective or even ineffective.)  Finally, these powders are often made from genetically-modified grains, which can further complicate your pet’s diet if you are striving for a non-GMO diet.

Other types of excipients you might find in your dog’s supplements

Other fillers

These are basically used to increase the volume of the preparation. Besides the ones mentioned above, some common fillers for dog food and supplements include:

  • Silicon
  • Talc
  • Lactose
  • Sorbitol
  • Calcium phosphate

Normally, these fillers are food grade, but they rarely serve a useful purpose in your supplements.  In addition, the fewer non-essential ingredients, the better so as not to introduce additional substances into your pet’s diet.  For example, we now know that some talc formulations are carcinogenic even though they were considered harmless in the past.  Finally, you don’t know how your pet’s body will react to any given ingredient either immediately or after taking it or over the long term.  So, it is best to avoid all ingredients that aren’t required for the manufacturing or preservation of the supplement.


As the name suggests, binders bind the components of a supplement into a tablet form. Some common examples are:

  • Honey
  • Gum Arabic
  • Lecithin
  • Sorbitol

Many commonly-used binders (including honey and sorbitol from the list above) contain sugars and should be avoided.  Others have no known harmful effects. 


These substances aid in the swelling of tablets and thus in breaking them apart to ease the absorption process in the gastrointestinal tract of your dog. Some common examples are:

  • Potato starch
  • Corn starch
  • Sodium starch glycolate
  • Sodium carboxy-methylcellulose
  • Alginic acid
  • Crospovidone

The listed starches and alginic acid are carbohydrates and should be avoided for the same reasons sugars should be.  The other examples are associated with a range of side-effects, including rashes, allergies, asthmaattacks and even hardening of arteries and the occurrence of plaque formation.


Lubricants aid in the filling of capsules and tablets and their release from dies and molds during manufacturing and can be helpful in enhancing the dissolving time of tablets.  Lubricants are, thus, essential for the manufacture of many supplements—there’s just no other way to get the active ingredient into the capsule without them.  So, it is best to choose lubricants that will have no harmful effect on your dog’s health and fit with your dog’s overall diet.  In addition to MCC (discussed above), the following vegetable-origin lubricants are recommended for your Cushing’s dog:

  • Stearic acid
  • Calcium stearate
  • Magnesium stearate


Powdered, liquid and chewable supplements often contain sweeteners. These may include:

  • Sorbitol
  • Sucrose
  • Maltrin
  • Maltodextrin
  • Fructose

All of these are sugars or metabolize into sugars and, therefore, should be avoided in your Cushing’s dog.

Coloring agents

Color additives are mainly for marketing purposes, to make the product attractive.  But, they may also serve a useful purpose in avoiding confusion with other tablets at the time of administration.  Color additives can be of vegetable origin (for example, from carrots or beets) or synthetic origin.

Coating materials

Coating materials play a vital role in:

  • Enhancing shelf life
  • Protecting from moisture
  • Ease in swallowing
  • Avoiding disintegration      

Coating agents are essential for the manufacture of most tablet supplements, and most coating agents are safe.  However, you should avoid products that use confectioners glaze, pharmaceutical glaze or natural glaze, as these can be difficult for some dogs to digest.


Preservatives can extend the life of your supplements and are, thus, useful (and sometimes essential) ingredients.  However, you should avoid selenium, sulfur, vitamin C and vitamin E as these are, in fact, active in the body (despite appearing in the “inactive ingredients” list) and may have undesired effects and interactions.

Excipients, you need not worry about

There are some inactive ingredients that are safe to use in dog supplements, including those listed below.   

Dicalcium phosphate

Dicalcium phosphate is helpful for the healthy functioning of your dog’s kidneys. Moreover, it provides a good source of calcium and magnesium that is suitable for balanced pet food. 

Stearic acid

As mentioned above, stearic acid is used in dog supplements to provide emulsification, lubrication, and softness. In the amounts typically included in supplements, it imposes minimum to no side effects on your dog.

Magnesium stearate

As mentioned above, magnesium stearate serves as a flow agent or lubricant in dog supplements and improves the consistency of the formulation. Furthermore, it delays the absorption of active ingredients until they get to their target sites.

Silicon dioxide

Silicon dioxide (amorphous form) is safe for dogs in amounts found in supplements. In excessive quantities (much greater than would be found in supplements), your dog might have mild gastrointestinal discomfort.

Microcrystalline cellulose

Microcrystalline cellulose is used as a filler and flow agent in the manufacturing process of supplements. As it is completely indigestible by dogs and other domestic animals, it is safe for your dog.


Stevia is not harmful to dogs. However, if your dog ingests it in large amounts, he might get a disturbed stomach and diarrhea.

 Final Thoughts

As much attention should be paid to the “inactive” ingredients as to the “active” ones to avoid harm to your dog.  Non-essential excipients should be avoided, essential excipients should be the best ones available to accomplish their purposes and harmful excipients should be avoided.  If your dog is taking prescribed medications, you should check with your veterinarian and/or pharmacist to ensure no interactions between those medications and any excipients of concern.