Medically reviewed by Dr Zeeshan Afzal (MBBS, General Practitioner) — Medical Content Reviewer, Welzo.
Written by: The Welzo Longevity Editorial Team | Last updated: July 2026
Declared interest: Welzo sells supplements, and several of our products contain excipients discussed below — NMN Pro 1000 uses an HPMC vegetable capsule and vegetable magnesium stearate. We have not written this to sell you a "filler-free" alternative, because that category is largely a marketing construct. See our editorial policy.
Search "supplement fillers" and you will find a great deal of alarming content, most of it wrong. The excipients in a capsule matter far less than the things our longevity supplements guide and our NMN benefits, side effects and dosage guide are actually built around: dose, evidence, and whether the active is present at all.
Every product in the NMN supplements collection and the wider anti-ageing and longevity supplements category contains excipients, including NMN Pro 1000, and so does everything else in a sensible longevity stack. That is not a flaw in the formulation. It is how capsules are made.
The most-attacked ingredient in the category — magnesium stearate — is the subject of a persistent myth traceable to a single 1990 laboratory study that did not use magnesium stearate, was not conducted in humans, and does not support the claim made about it.
Meanwhile, the things that genuinely do warrant attention get comparatively little coverage: allergens, animal-derived components in products bought by vegans, a colouring banned as a food additive in the EU but still permitted in Great Britain, and bulking agents used to disguise underdosing. This guide separates the two.
The short answer
Most excipients are functional, necessary and harmless at the amounts used. The genuine concerns are narrower than the internet suggests: undeclared allergens, animal-derived components if you avoid them, titanium dioxide if you would rather not consume something the EU has banned as a food additive [1,2,3], and — most importantly — bulking agents used to pad out an underdosed product. The real problem is almost never the excipient itself. It is what the excipient is hiding.
Table of contents
An excipient is any ingredient in a product other than the active. They are not padding for the sake of it — most exist because without them the product could not be manufactured consistently or would not work as intended.
| Type | Function | Common examples |
|---|---|---|
| Flow agents / lubricants | Stop powder sticking to machinery so each capsule gets the right dose | Magnesium stearate, silicon dioxide |
| Binders | Hold a tablet together | Cellulose, dicalcium phosphate |
| Disintegrants | Make a tablet break apart so it can be absorbed | Croscarmellose sodium |
| Capsule shells | Contain the powder | HPMC (plant), gelatin (animal) |
| Bulking agents | Fill volume where the active dose is small | Microcrystalline cellulose, rice flour |
| Anti-caking agents | Prevent clumping | Silicon dioxide |
| Colours and coatings | Appearance, light protection, swallowability | Titanium dioxide, shellac, carmine |
Consider the arithmetic. A capsule holds a fixed volume. If the active dose is 50 mg and the capsule holds 500 mg of powder, something must occupy the remaining space — otherwise the powder shifts, doses vary between capsules, and the encapsulation machinery jams.
Products that genuinely contain nothing but active are usually either powders sold by weight, or high-dose single ingredients where the active fills the capsule anyway. Both are legitimate. Neither is evidence that a formulated product with a lubricant is inferior — which is why the Welzo Ultra Purity range is built around single ingredients at disclosed doses rather than around excipient claims.
The flow agent question is particularly worth understanding: without one, dose uniformity between capsules gets worse. An entirely "filler-free" capsule can therefore be less accurately dosed than one containing 1% magnesium stearate.
| Format | Excipients typically needed | Trade-off |
|---|---|---|
| Powder (sold by weight) | Few or none | Taste, measuring, less convenient |
| Capsule | Shell, flow agent, sometimes bulking | Convenient; volume limits dose |
| Tablet | Binders, disintegrants, coatings, often colours | Highest excipient load; can carry larger doses |
| Softgel | Shell (often gelatin), carrier oil | Good for oils; usually not vegan |
| Liquid | Preservatives, flavourings, sweeteners | Absorption arguments; shorter shelf life |
If excipient load genuinely matters to you, changing format is more effective than changing brand. A creatine or collagen powder sidesteps the question almost entirely; a coated tablet carries the most. This is also why we generally recommend powder for high-dose items in our cheap longevity stack — it is both cheaper per gram and simpler in composition.
This deserves its own section because it is the most widely repeated false claim in the supplement category, and it is used specifically to sell premium "stearate-free" products.
That magnesium stearate suppresses the immune system by damaging T-cells.
A single 1990 paper: Tebbey PW and Buttke TM, "Molecular basis for the immunosuppressive action of stearic acid on T cells", published in Immunology [4]. You can read the abstract yourself, and we would encourage it — the paper's own description of its methods settles the question fairly quickly.
There is also a species problem that undermines the extrapolation entirely: humans possess delta-9 desaturase, which converts stearic acid into oleic acid — the monounsaturated fat in olive oil. The mouse T-cells in that experiment lacked that pathway [5,6].
Worth noting as a matter of record: the paper subsequently carried a published erratum in the same journal [4]. That does not invalidate it — errata are routine — but it is a reminder that the single study underpinning an entire premium product category was not treated as settled even by its own publisher.
ConsumerLab's assessment is that laboratory conditions of this kind do not represent what happens in the body when you ingest normal amounts of stearic acid, let alone the far smaller amounts of magnesium stearate in a supplement, and that immune suppression from supplement-level magnesium stearate is highly unlikely and has not been reported [5]. A critical review reached the same conclusion, noting the 1990 paper is a perfectly reasonable piece of research that simply has nothing to do with magnesium stearate as an excipient [6].
Stearic acid is also not exotic. It occurs naturally in beef, cocoa butter, and many everyday foods, in quantities that dwarf what a capsule contributes.
Our position: we use vegetable magnesium stearate in NMN Pro 1000 and we are comfortable saying so publicly. Brands charging a premium for "stearate-free" formulations on the basis of that 1990 paper are selling a fear that the evidence does not support. If you prefer to avoid it for your own reasons, that is entirely legitimate — but it should be a preference, not a safety decision.
A softer variant holds that magnesium stearate blocks nutrient absorption by coating particles. It can slightly slow the rate at which a capsule dissolves, but controlled dissolution and bioavailability work does not show a meaningful reduction in absorption when it is used appropriately at typical levels [5,6]. Rate and extent of absorption are different things.
This is the most legitimate concern on the list and the least discussed. Lactose appears as a filler in some products, which matters for anyone lactose intolerant. Wheat-derived starch, soy derivatives and shellfish-derived components all appear in supplements. UK allergen labelling requirements apply, so declared allergens must be identifiable — read the list rather than assuming.
Gelatin capsules are bovine or porcine. Magnesium stearate can be plant or animal-sourced, so vegans should look for "vegetable magnesium stearate" specifically. Shellac is an insect resin, carmine an insect-derived colour, and lactose is dairy. None of these are safety issues; all of them matter if you avoid animal products. Our full treatment is in vegan longevity supplements, and plant-based options sit in the vegan and plant-based collection.
Colours serve no nutritional purpose in a capsule you swallow whole. Certain artificial colours carry mandatory warning labelling in the UK and EU regarding possible effects on activity and attention in children. There is no strong reason to accept them in a supplement, and their presence tells you something about how the product was formulated.
This is the one that costs you money. Where a product is heavily bulked and the active dose is low, you are buying rice flour at supplement prices. The tell is a large capsule with a small stated dose, or a long "other ingredients" list on a product whose active should fill the capsule.
This is genuinely useful for UK readers and almost never explained properly.
Titanium dioxide (E171) is a white colouring used in food, supplements and medicines. In May 2021 the European Food Safety Authority concluded it could no longer be considered safe as a food additive, being unable to rule out genotoxicity and therefore unable to establish a safe daily intake [1,3]. The European Commission banned its use as a food additive, with the prohibition applying from 7 August 2022 [1,2].
Great Britain did not follow. In March 2022 the Food Standards Agency and Food Standards Scotland concluded, after reviewing the evidence, that no safety concerns had been identified and that regulation would not change [2,3]. Titanium dioxide accordingly remains an authorised food additive in Great Britain [3], while Northern Ireland continues to follow EU rules. It also remains permitted in medicines in the EU, to avoid shortages while alternatives are developed [1].
What to do with that: two respected regulators looked at the same evidence and reached different conclusions. That is a legitimate scientific disagreement rather than a scandal, and we are not going to tell you which one is right. What we will say is that E171 serves a purely cosmetic and light-protective function in most supplements, alternatives exist, and if you would rather not consume something the EU has withdrawn approval for, you can simply read the label and choose otherwise. In Great Britain that choice is yours to make, because it remains legal here [2,3].
| Excipient | What it is | Should you care? |
|---|---|---|
| Magnesium stearate | Flow agent; magnesium salt of stearic acid | No safety concern at supplement levels [4,5,6]. Check "vegetable" if vegan. |
| Silicon dioxide | Anti-caking agent | No — inert at the amounts used |
| HPMC / vegetable cellulose | Plant-based capsule shell | No — this is the vegan-friendly option |
| Gelatin | Capsule shell from bovine or porcine collagen | Only if you avoid animal products |
| Microcrystalline cellulose | Bulking agent from plant fibre | Not in itself — but check it is not displacing active |
| Rice flour / maltodextrin | Bulking agents | As above; watch the ratio to active |
| Titanium dioxide (E171) | White colouring and light protection | Banned as a food additive in EU; still authorised in Great Britain [1,2,3]. Your call. |
| Lactose | Milk-derived filler | Yes if lactose intolerant or vegan |
| Shellac | Insect-derived glaze | Only if vegan |
| Carmine (E120) | Insect-derived red colour | Only if vegan, or you avoid it on principle |
| Artificial colours | Cosmetic only | No functional benefit in a swallowed capsule |
| Croscarmellose sodium | Disintegrant | No — it helps the tablet work |
| Stearic acid | Lubricant; a common dietary saturated fat | No at these amounts |
Focusing on excipients is, for most people, worrying about the wrong thing. Here is where the actual risk sits.
An ingredient present at a fraction of the studied dose is the most common way a legitimate compound becomes a useless product. No excipient causes this; formulation economics do.
Where a label gives a blend total rather than per-ingredient amounts, you cannot verify that anything is present at a meaningful dose. This is the single most consequential labelling practice in the industry, and it is legal.
Researchers at the National University of Singapore tested commercial NMN and urolithin A supplements against label claims and found measured NMN content ranging from undetectable to 99.2% of total sample weight, with deviation from label claim spanning −100% to +11.2% — several contained no detectable active at all [7,8].
Every excipient in those products was probably declared correctly. The defence against this is not an ingredient list but a batch-specific certificate of analysis — see how to read a certificate of analysis and third-party testing: what it means and what it doesn't.
It is worth asking who benefits from the alarm. "Filler-free" and "no magnesium stearate" are premium positioning claims. They cost a brand very little to make, require no clinical evidence, and justify a higher price against competitors whose products are functionally equivalent.
Compare that with the claims that would actually cost money to support — third-party batch testing, clinically studied doses, published certificates — and the appeal of the excipient angle becomes obvious. It is the cheapest available way to sound rigorous.
This is the same pattern we describe in why supplements are expensive: costs that exist because the market rewards them rather than because they improve the product. Being sceptical of filler panic is not being relaxed about quality — it is directing scepticism at the things that actually vary between products.
Then do the thing that matters more than all seven: ask for the certificate of analysis.
For most other people, excipients are simply not where the risk or the value lies. Spend the attention on dose, evidence and verification instead — see longevity supplements that probably don't work and how much a longevity stack costs. The wider catalogue sits in all supplements and vitamins.
If you are building or reviewing a routine: how to start longevity supplements covers sequencing, the supplement timing chart and can you take supplements together cover practicalities, and how long supplements take to work sets realistic expectations. For specific situations, see shift work, women over 40 and men over 50. For evidence assessments of individual compounds: is NMN a scam? and does resveratrol actually work?
Speak to your GP or pharmacist before starting any supplement if you take prescription medication, have an existing medical condition, or are pregnant or breastfeeding. If you have a diagnosed allergy, check labels carefully and ask a pharmacist if an ingredient is unclear.
Seek medical advice if you experience a reaction after taking a supplement — rash, swelling, breathing difficulty, or significant digestive upset. Stop taking the product, keep the packaging and batch number, and note that adverse reactions can be reported to the Food Standards Agency. If you experience symptoms of a severe allergic reaction such as difficulty breathing or swelling of the face or throat, call 999.
No, on current evidence. The claim that it suppresses immunity traces to a single 1990 in vitro study that used stearic acid rather than magnesium stearate, on isolated murine cells, at concentrations unachievable through diet [4,5,6]. Humans convert stearic acid to oleic acid via an enzyme pathway those mouse cells lacked. ConsumerLab's assessment is that immune suppression from supplement-level magnesium stearate is highly unlikely and has not been reported [5].
It can slightly slow how quickly a capsule dissolves, but controlled dissolution and bioavailability work does not show meaningful reduction in absorption at typical usage levels [5,6]. The rate of absorption and the total amount absorbed are different things, and it is the second that matters.
Genuinely: declared allergens you react to; animal-derived components if you avoid them; artificial colours, which serve no purpose in a swallowed capsule; and heavy bulking where the active dose is small relative to capsule size. Titanium dioxide is a personal choice given the UK–EU regulatory divergence [1,2,3]. Most other excipients are functional and harmless at the amounts used.
No. The EU banned titanium dioxide (E171) as a food additive from 7 August 2022 following EFSA's conclusion that it could no longer be considered safe [1]. Great Britain did not follow: the Food Standards Agency and Food Standards Scotland concluded in March 2022 that no safety concerns had been identified, and it remains an authorised food additive in Great Britain [2,3]. Northern Ireland follows EU rules.
Not automatically. A capsule needs something to occupy its volume and a flow agent to ensure consistent dosing — without one, dose uniformity between capsules can be worse. Genuinely excipient-free products are usually powders sold by weight or high-dose single ingredients where the active fills the capsule. Both are fine; neither makes a properly formulated product inferior.
HPMC (hydroxypropyl methylcellulose) and other vegetable cellulose capsules are plant-derived and suitable for vegans. Gelatin capsules are bovine or porcine. If a label says only "capsule shell", check the product page or ask before buying — see vegan longevity supplements.
Yes at the amounts used. It is an anti-caking agent that prevents powder clumping, is inert, and appears in many foods. It is one of the more commonly attacked excipients online without a substantive evidence base behind the concern.
Compare the stated active dose against the capsule size. If a capsule holds several hundred milligrams of powder and the active is 50 mg, the balance is bulking agent. Also check for proprietary blends, where per-ingredient amounts are hidden — that is a more consequential problem than any individual excipient.
Some people report that certain fillers are less well tolerated, and this is worth taking seriously as an individual matter even though population-level evidence is limited. If you have a diagnosed gastrointestinal condition, discuss it with your clinician, and consider powders or minimal-excipient formats if capsules consistently cause problems.
Whether the active is present at a dose supported by evidence, and whether the product actually contains what it claims. Independent testing has found supplements containing no detectable active ingredient at all [7,8] — and every excipient in those products was probably declared accurately. A batch-specific certificate of analysis is the check that matters most; see how to read a certificate of analysis.
Medical disclaimer
This article is for general information and does not constitute medical advice, diagnosis or treatment. Regulatory positions on food additives differ between Great Britain, Northern Ireland and the EU and are subject to change — always check current guidance. Nothing here should be taken as advice to disregard a diagnosed allergy or intolerance: if you have one, read labels carefully and seek pharmacist advice where an ingredient is unclear. Always consult a qualified healthcare professional before starting any new supplement, particularly if you take prescription medication, have an existing medical condition, or are pregnant or breastfeeding. If you experience symptoms of a severe allergic reaction, call 999. Reviewed for medical accuracy by Dr Zeeshan Afzal. See the full Welzo medical disclaimer.
All product photography in this article is owned by Welzo and served from the Welzo media library. Regulatory positions correct at the time of publication and subject to change.
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