The Most Common Additives and Fillers Found in Supplements (and How to Spot Them)

If you have ever flipped over a supplement bottle and felt your eyes glaze over halfway down the ingredient list, you are not alone. The first few items are usually the active ingredients you bought the product for. The last few are typically fillers, binders, flow agents, anti-caking agents, and capsule shell components. Some of those are fine and necessary. Some are worth knowing about. A few are worth avoiding.

This is the practical, plain-English breakdown of the most common supplement additives, what each one actually does, and how to read a label without needing a chemistry degree.

You take a supplement to put one or more specific things into your body — vitamin D, magnesium, an adaptogen, a probiotic strain. Anything else in the capsule that you did not specifically buy is a co-passenger. Most are inert and harmless. Some have legitimate manufacturing reasons. A few have either gut-disturbing effects on sensitive people or have been the subject of recent regulatory reassessment in the UK.

Knowing the names lets you do two things: judge the overall quality of a product at a glance, and avoid specific additives that do not work for your body.

Microcrystalline cellulose (E460)

One of the most common fillers in capsule and tablet supplements. Made from refined wood pulp or cotton, it is essentially purified plant fibre. EFSA has authorised it as a safe food additive. It is inert, used to bulk out capsules to a consistent volume, and the body does not absorb it. Generally fine.

Magnesium stearate

The most controversial-by-internet-comment filler in the supplement world. It is a "flow agent" — a small amount of magnesium stearate (typically less than 1% of the capsule weight) prevents the powder from sticking to manufacturing machinery and ensures consistent capsule fill weight.

Honest version: food regulators (EFSA, the FSA, the FDA) permit magnesium stearate at the trace levels used in supplements. The internet concern about it "blocking absorption" comes from older laboratory studies that have not held up under realistic dietary conditions. That said, many premium supplement makers have moved away from it because (a) it is unnecessary for small-batch production where mechanical issues are less of a problem, and (b) consumer preference.

Maltodextrin: a starch-derived carbohydrate used as a carrier.

Silicon dioxide (E551)

An anti-caking agent — keeps powder dry and free-flowing. Used in tiny amounts. EFSA reviewed it in 2018 and confirmed it is safe at typical dietary levels. Generally fine.

Titanium dioxide (E171)

This is the one that has changed in the last few years. Titanium dioxide was historically used as a white colouring and opacifier in tablet coatings and capsule shells. In May 2021, EFSA concluded that it could no longer be considered safe as a food additive, primarily due to genotoxicity concerns. The EU banned it in food and food supplements from August 2022 (this also applies in Northern Ireland). Great Britain's regulators reviewed the same evidence and did not ban it.

Either way, the global trend among premium supplement makers is to remove it, and finding it on a label of a product manufactured in 2024 or later is increasingly unusual. Worth checking.

Hydroxypropyl methylcellulose (HPMC)

This is what most modern vegan capsule shells are made from. It is plant-derived, replaces traditional gelatine (which comes from animal collagen), and is inert in the gut. Our capsules use HPMC shells. Standard, safe, and the right choice if you want vegan capsules.

Gelatine

The traditional capsule shell material, made from animal collagen (typically beef or pork). Functionally fine, but rules out vegan and most halal/kosher buyers. The shift to HPMC over the last decade has been driven mostly by consumer preference rather than safety concerns.

Stearic acid and palmitic acid

Naturally-occurring saturated fatty acids used as lubricants and binders. Found naturally in olive oil, palm oil, and animal fats. Generally inert at supplement levels. Vegan unless animal-sourced (most modern supplement-grade is plant-derived).

Stoneground brown rice flour: a food ingredient used as a bulking agent.Bamboo extract: a plant source of silica, used as a flow agent.

The short list of additives where it is worth checking and asking why they are present:

• Titanium dioxide (E171) — banned in the EU and Northern Ireland since 2022; Great Britain has not banned it.
• Artificial colours (E102 tartrazine, E110 sunset yellow, E129 allura red, others) — historically associated with hyperactivity in some children (Southampton study, McCann et al., 2007) and required warning labels in the UK. There is rarely a good reason for them in a supplement.
• Aspartame, sucralose, acesulfame K and steviol glycosides are permitted sweeteners; the label names the one used.
• Hydrogenated vegetable oils — partially hydrogenated oils introduce trans fats. Avoid.
• Worth asking why they are needed.

1. Filler list short and recognisable? Whole-food fillers like rice flour or bamboo extract are a stronger signal than a long list of E-numbers.
2. Does it state non-GMO? Particularly relevant if maltodextrin or ascorbic acid is on the label.
3. Vegan capsule shell (HPMC) or animal gelatine? Personal preference, but worth knowing.

Most of our capsules use HPMC vegan shells with brown rice flour; the full ingredient list is on every product page. The full ingredient list for every product is published on the product page so you can see exactly what is in it before you buy. The Spirulina capsules are a clean, single-ingredient example, and the Vitamins Multi formula shows the full ingredient stack of a complete daily multi.

Most additives in a well-made supplement are inert, necessary, and safe. A few are worth knowing about — titanium dioxide, artificial colours, certain artificial sweeteners, and unnecessary emulsifiers.