What the list is and where it comes from

The rule is 21 CFR 101.4(g). It requires that ingredients which are not dietary ingredients ("excipients, fillers, artificial colors, artificial sweeteners, flavors, or binders") appear in the ingredient list. When some source ingredients are already shown inside the Supplement Facts panel, the remainder appears below it under the heading "Other ingredients."

Two things follow, and both are useful.

The list is in descending order by weight. Under 21 CFR 101.4(a)(1), ingredients are listed "by common or usual name in descending order of predominance by weight." FDA's labeling guidance repeats it: "You must list the ingredients in descending order of predominance by weight." So the first item in the Other ingredients list is the heaviest one.

It is where allergens surface. Major food allergen labeling applies to dietary supplements, and the Other ingredients line is typically where a soy, wheat, milk or fish derivative would show up if it is present. There are nine major food allergens in the United States: milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, soybeans, and sesame, which became the ninth effective January 1, 2023.

What each common item is doing

Magnesium stearate

The most argued-about ingredient in the category, and the one where the facts are clearest.

What it is: the magnesium salt of stearic acid. FDA affirms it as generally recognized as safe as a direct human food ingredient, at 21 CFR 184.1440. The regulation lists its functions as "lubricant and release agent," "nutrient supplement" and "processing aid."

What it does: it keeps powder from sticking to the machinery. Tablet presses and capsule fillers run at high speed with tight tolerances; without a lubricant, powder adheres to punches and dies, doses become inconsistent, and production stops. It is used in small amounts, and the regulation sets no numeric cap, requiring only that use be consistent with good manufacturing practice.

The immune-suppression claim. You will find the assertion that magnesium stearate suppresses the immune system, usually citing a 1990 study. That study exists. It is Tebbey and Buttke, published in Immunology in 1990, and here is what it was: cultured mouse B and T cells, in a dish, exposed to free stearic acid, not magnesium stearate. The researchers were investigating why T cells, which lack a particular enzyme, accumulate saturated fatty acids in their membranes. It was not an oral study or a human study, and it was not a study of a supplement excipient.

Taking a cell-culture result with a different substance in a different species and applying it to a few milligrams swallowed in a tablet is not a small extrapolation, because it stacks several unrelated leaps together.

The absorption claim. The other common assertion is that magnesium stearate blocks absorption. There is a grain of something real underneath it: magnesium stearate is hydrophobic, and formulation research has shown that varying its level can measurably slow how fast a tablet dissolves in early-stage laboratory testing. But two randomized crossover studies in human volunteers deliberately varied magnesium stearate levels and found the resulting formulations bioequivalent, with no meaningful difference in peak concentration or total exposure. Those were drug studies, not supplement studies, which is worth saying plainly. What they show is that a measurable effect on a dissolution curve did not translate into a measurable effect on how much got absorbed.

The reasonable position: magnesium stearate is a manufacturing aid with a long history of use, used in small amounts, and the two most common claims against it rest on a misread cell-culture study and on an in-vitro effect that human data did not bear out.

Silicon dioxide

Also called silica. An anticaking and flow agent: it keeps powder from clumping in humid conditions so that each capsule gets filled consistently.

It is a listed food additive at 21 CFR 172.480, permitted "in an amount not to exceed 2 percent by weight of the food." One of its expressly permitted uses is as an adsorbent for certain vitamins in tableted dietary foods, which is exactly the supplement application.

Microcrystalline cellulose

Purified plant cellulose, used as a binder and a filler. It appears in FDA's inventory of substances added to food, with listed technical effects including anticaking and free-flow agent, stabilizer and thickener.

In a capsule it often serves as bulking material, which is the legitimate version of "filler." A capsule has a fixed volume; if the active ingredient occupies less than that volume, something has to occupy the rest or the capsule will not fill consistently. Cellulose is a reasonable choice.

Microcrystalline cellulose is also, chemically, insoluble fiber. It is not doing anything nutritional at the amounts used, but it is not a foreign substance either.

Stearic acid

A fatty acid found in beef fat, cocoa butter and many vegetable oils. GRAS-affirmed at 21 CFR 184.1090, where it is produced from tallow or hydrogenated vegetable oils. In tablets it serves a lubricant function similar to magnesium stearate.

A small precision point: the CFR entry describes its food use as a flavoring agent and adjuvant. Its role as a tablet lubricant is a pharmaceutical function rather than the one described in that food listing: the same substance, used for a different purpose.

Binders and disintegrants generally

You will also see items like croscarmellose sodium, dicalcium phosphate, silica-based flow agents and various celluloses. Broadly, these fall into recognizable jobs:

• Binders hold a tablet together so it survives shipping
• Disintegrants make it fall apart once swallowed, which is the opposite job, and both are needed
• Fillers occupy volume
• Coatings protect against moisture, mask taste, or delay release

A tablet is a small engineering problem: hold together in the bottle, come apart in the stomach, and deliver a consistent dose every time. The Other ingredients list is largely the solution to that problem.

Colors, and the one to watch

Colors are the part of this list where something is in motion.

Titanium dioxide is a white pigment used as an opacifier and colorant. As of September 2026 it remains permitted in the United States as a color additive, under 21 CFR 73.575, with the quantity limited to one percent by weight of the food.

It is, however, under active FDA review. It appears on FDA's list of select chemicals in the food supply under review, at the scientific assessment stage, and a color additive petition asking FDA to revoke the listing, filed in April 2023 by a group of public-interest organizations, is pending. FDA's own published position, from a page last updated in March 2024, is that it "did not identify concerns related to potential genotoxicity" and that it allows the safe use of titanium dioxide according to the specifications and conditions in the regulation.

The regulatory picture elsewhere is different, and that difference is why the ingredient is controversial. This is a live file; if it matters to you, check FDA's current status rather than relying on any article, including this one.

Synthetic dyes are also moving. FDA issued an order revoking the color additive listing for FD&C Red No. 3 in January 2025, under the statutory provision that bars authorization of a color additive found to induce cancer in animals. Compliance dates are January 15, 2027 for foods and January 18, 2028 for ingested drugs. In April 2025, HHS and FDA announced measures to phase out petroleum-based synthetic dyes from the food supply, and several other FD&C colors are at a risk-management stage on FDA's review list.

For a supplement buyer the practical point is simple: colors in a supplement are cosmetic. They do nothing for you. A product without them has given up nothing you were going to benefit from.

The form determines the list

Before you judge a long list, look at what you are holding. Different formats need different amounts of help.

Capsules need the least. The shell provides the structure, so the powder inside mainly needs to flow consistently into it. A short list (a flow agent, maybe a filler to occupy volume) is normal and expected.

Tablets need the most of the mechanical excipients. Powder has to be compressed into something that survives a supply chain and then breaks apart on schedule. That takes binders, disintegrants, lubricants and often a coating. A tablet with six or eight other ingredients is doing ordinary tablet things.

Softgels carry their own set: gelatin or a plant alternative, glycerin as a plasticizer, often an opacifier to protect a light-sensitive oil.

Powders typically need anticaking agents and, if they are meant to be palatable, flavors, sweeteners and sometimes colors. A powder you mix into water is asking more of the flavor system than a capsule you swallow.

Gummies have, by a wide margin, the longest other-ingredient lists of any format: sugars or sugar alcohols, gelatin or pectin, acids, flavors, and usually colors. That is inherent to making something taste like candy. Gummies are a legitimate choice for people who will not take capsules, and they involve a real trade-off in what else you are consuming. Read that list specifically.

So the right comparison is within a format. A capsule with eight excipients raises a question that the same eight in a tablet does not.

How to read the list

Check the order. First is heaviest. If cellulose or rice flour or maltodextrin leads the list, the bulk of what you are swallowing is bulk.

Compare length to purpose. A capsule needs fewer excipients than a tablet, because it does not have to be compressed and held together. A tablet with eight other ingredients is not suspicious; a capsule with eight might be worth a second look.

Scan for allergens. This is the line where soy, wheat and milk derivatives appear.

Notice colors and flavors in a product you swallow whole. A coated tablet with a color has a reason: light protection, or distinguishing products. A flavored chewable has an obvious reason. A plain capsule with dyes in it has less of one.

Do not treat a short list as proof of quality. "No fillers" is a marketing line, not a quality metric. Some products need very little; others get a short list by using a capsule that is already doing the work a tablet's excipients would do. Neither tells you whether the active ingredient is any good.

Keeping this in proportion

The Other ingredients list is worth reading, and it is not where the important variance in supplement quality lives.

The things that differ between a well-made product and a poorly-made one are upstream: whether the ingredient is what it says it is, whether the amount is meaningful, whether the raw material was tested for contamination, and whether the company can produce a certificate of analysis for the lot you bought. Those are the questions with real spread in the answers.

Excipients are a smaller question with a narrower range of answers, since these are common, long-used, generally recognized substances doing unglamorous mechanical jobs. If you have a specific reason to avoid one, avoiding it is easy and plenty of products will accommodate you. If you do not, the list is mostly telling you how the tablet was built.