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 describes products in our own range as third-party tested. This article explains exactly what that phrase can and cannot support — including where our own claims sit and how to check them. See our editorial policy.
"Third-party tested" is the most reassuring phrase in supplement marketing and one of the least precise. It is also the check that everything in our longevity supplements guide and our NMN benefits, side effects and dosage guide depends on — because evidence for an ingredient means nothing if the capsule does not contain it.
Welzo describes products in its own range as third-party tested — the NMN supplements collection, NMN Pro 1000 and the wider anti-ageing and longevity supplements category, all of which sit within the longevity stack framework. This article explains exactly what that phrase can and cannot support, including for our own claims.
The phrase appears on premium products and on products that have never had a finished capsule near an independent laboratory, and nothing in UK law prevents either. Below: the three quite different things it is used to describe, the certification programmes that actually stand behind it, and — the part most guides skip — the specific claims it does not support no matter how prominently it is displayed.
The short answer
"Third-party tested" has no legal definition. It can mean a rigorous batch-by-batch programme with published results, or a single test done once on one batch years ago, or a facility audit that never touched the finished product. The three things it gets used to describe — facility certification, product content verification, and banned-substance screening — answer completely different questions, and holding one tells you nothing about the others. What matters is which programme, tested by whom, how often, and whether you can verify it yourself.
Table of contents
There is no statutory definition of "third-party tested" in UK or EU food law, no register of who may use it, and no enforcement mechanism specific to the claim. A brand that sent one bottle to an independent laboratory in 2021 can use the phrase indefinitely.
This matters because the underlying problem it is meant to solve is real. 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 products contained no detectable active ingredient at all [1,2]. That is the risk the phrase is meant to address, and the reason it appears so prominently on products in the longevity supplements category, where actives are expensive and impossible to judge by appearance.
So the claim addresses a genuine risk. It just does not, by itself, tell you whether that risk has been addressed for the product you are holding.
This is the source of most consumer confusion, and brands are rarely in a hurry to clear it up.
Good Manufacturing Practice certification audits the manufacturing site: sanitation, documentation, ingredient traceability, equipment calibration, process controls. It asks whether the facility operates to standard.
What it does not do is test your product. GMP registration confirms process controls but does not test the finished product for contaminants or banned substances [5,6]. A facility can be impeccably certified and still produce a batch that was blended incorrectly.
This tests a finished product for identity, potency, purity and specified contaminants. It asks whether the product contains what the label claims and nothing it shouldn't. This is what most consumers assume "third-party tested" means, and it is the question our companion guide, how to read a certificate of analysis, is built around.
A completely separate question, relevant to anyone subject to drug testing. It screens for substances prohibited in sport, which is not the same panel as purity and potency testing and will not detect an underdosed product.
| Type | Question it answers | What it misses |
|---|---|---|
| Facility / GMP certification | Is this factory well run? | Everything about your specific batch [5,6] |
| Product content verification | Does the bottle contain what it claims? | Banned substances; whether the ingredient works |
| Banned substance screening | Is it contaminated with prohibited compounds? | Whether the active is present at the stated dose |
A product can hold all three, one, or none — and the marketing language for all three is frequently identical.
Developed in 2008 for the elite sports nutrition industry in conjunction with UK Anti-Doping, Informed Sport tests every single batch of a certified product before it is released to market, screening for more than 250 substances banned in sport, using ISO 17025 accredited methods. Testing is carried out at LGC's anti-doping laboratories, with UK accreditation granted by UKAS. After certification, the programme continues blind testing by purchasing certified products from retail and re-analysing them, and certified batches are searchable by batch number on the programme's website and app [3,4].
The programme exists because contamination is a documented problem: Informed Sport cites analysis attributing 8% of all anti-doping violations between 2005 and 2022 to product contamination [7].
Informed Choice uses the same testing procedures and technologies as Informed Sport, but the sampling model differs materially: rather than testing every batch before release, it operates through monthly blind sampling, with the laboratory purchasing product from retail outlets [3,4].
That is a meaningful distinction that the similar branding obscures. For an elite athlete under strict liability, "every batch tested before release" and "a batch sampled each month" are not equivalent assurances.
NSF operates tiered programmes: a contents-tested certification confirming label accuracy and contaminant limits; a GMP registration that audits facilities rather than products; and NSF Certified for Sport, which tests on a lot-by-lot basis for banned substances [5,6]. As with Informed Sport, the sport-specific tier is the most stringent and the facility registration is the least product-specific.
USP's verification programme covers identity, potency, purity and dissolution alongside facility auditing, and is widely regarded as the most pharmaceutical-style consumer mark. It operates periodic risk-based surveillance of marketed product rather than lot-by-lot release testing, and does not screen for the hundreds of substances prohibited in sport [5,6].
| Programme | Tests | Frequency | Best for |
|---|---|---|---|
| Informed Sport | 250+ banned substances [3,4] | Every batch before release, plus retail blind testing | Elite and drug-tested athletes |
| Informed Choice | Same panel as Informed Sport | Monthly blind sampling from retail | Active people not subject to testing |
| NSF Certified for Sport | Banned substances plus contents | Lot-by-lot [5,6] | Athletes, particularly US sport |
| NSF Contents Certified | Label accuracy, contaminants | Periodic with annual review | General quality assurance |
| USP Verified | Identity, potency, purity, dissolution | Periodic surveillance [5,6] | General quality assurance |
| GMP / facility certification | Manufacturing processes | Periodic audit | Baseline — not product testing |
| Unbranded "third-party tested" | Unknown | Unknown | Ask for the COA |
If you remember one operational detail from this article, make it this one.
Testing is expensive per batch. A brand can test once, publish an excellent certificate, and continue shipping for years without retesting. The document remains genuine; it simply stops describing what is being sold.
This is why the Informed Sport model — every batch tested before release, with batch numbers publicly searchable [3,4] — is structurally stronger than any one-off test, regardless of how impressive the one-off looks. It is also why the single most useful question you can ask a brand is not "is it tested?" but "how often, and can I check my batch?"
The practical test: take the lot number from your product and try to verify it. If a programme lets you search that number and confirm the batch was tested, the claim is real and current. If nothing on the packaging can be checked against anything, the claim is an assertion. How to read a certificate of analysis covers what to do with the document once you have it.
In almost every case, the brand pays the laboratory. That is how the industry works and there is no realistic alternative — but it is a structural conflict worth naming, and it is the same conflict we flagged when discussing industry-funded collagen trials in supporting skin ageing from the inside.
What mitigates it:
A programme with none of these mitigations is a brand paying for a result and choosing what to show you.
| You are | What you need | Why |
|---|---|---|
| A tested athlete or drug-tested professional | Informed Sport or NSF Certified for Sport, batch verified | Strict liability applies regardless of intent; Informed Sport cites contamination as accounting for 8% of anti-doping violations 2005–2022 [7] |
| A recreational gym-goer | Informed Choice or equivalent, plus a product COA | Lower stakes, but contamination risk is real |
| Buying longevity or general health supplements | A published batch-specific COA for the finished product | Content verification is the relevant risk [1,2] |
| Buying botanicals, mushrooms or seaweed | COA including heavy metals and microbiology | Plant material concentrates soil and water contaminants [10] |
| Buying commodity vitamins from a reputable retailer | Basic assurance is usually sufficient | Simple, well-established supply chains carry lower risk |
If you compete in tested sport, the rules hold you responsible for what is in your body regardless of intent, fault or negligence. That is why batch-level certification exists, and why "the brand said it was tested" is not a defence. If this applies to you, use a programme with a searchable batch database and check every purchase — see also supplements for endurance athletes.
If a brand cannot get you past step two, you have your answer. Related reading: supplement fillers explained and why supplements are expensive.
We publish certificates of analysis on product pages — the one for NMN Pro 1000 is linked directly from its listing — and we would encourage you to open it and apply every check above rather than taking the claim on trust. Where you want to know which specific programmes a given product carries, that information belongs on the product page, and if it is not there you should ask us. The full own-brand range is in Welzo Ultra Purity, with our ingredient quality and purity certifications set out separately.
For guidance on what to actually buy once quality is established: the minimal supplement stack and the cheap longevity stack. For a sceptical counterweight: longevity supplements that probably don't work 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. No certification addresses whether a product is appropriate for you specifically — testing verifies contents, not suitability.
If you experience an adverse reaction to a supplement, stop taking it and seek medical advice. Keep the packaging and batch number, which will materially assist any investigation, and adverse reactions can be reported to the Food Standards Agency.
Legally, nothing specific — there is no statutory definition or register governing the phrase. In practice it is used to describe three different things: facility audits, product content verification, and banned-substance screening. These answer different questions, and a product holding one may hold none of the others. The useful follow-up questions are which programme, how often, and can you verify your batch.
No, and this is the most common confusion. GMP certification audits the manufacturing facility — sanitation, documentation, traceability, equipment calibration. It confirms process controls but does not test the finished product for contaminants or banned substances [5,6]. A facility can be properly certified and still release a batch that was blended incorrectly.
They use the same laboratory, methods and substance panel, but differ in sampling frequency. Informed Sport tests every single batch before release to market, plus ongoing blind testing of retail purchases. Informed Choice operates through monthly blind sampling from retail rather than testing every batch [3,4]. For anyone subject to drug testing, that difference is significant.
If you compete in tested sport or are subject to workplace drug testing, yes — strict liability means you are responsible for what is in your body regardless of intent, and Informed Sport cites contamination as accounting for 8% of anti-doping violations between 2005 and 2022 [7]. If you are not tested, banned-substance certification is less relevant than straightforward content verification.
No. Testing confirms what is in the product, not what the product does. A supplement can be verifiably exactly what it claims and still have weak or absent evidence for the ingredient itself — a meta-analysis of eight NMN trials found no significant effect on glucose or lipid markers, for example [8]. Quality and efficacy are separate assessments.
Ask which named programme. If it is Informed Sport or a similar scheme, search your batch number on the programme's own database [3,4]. If it is an unbranded claim, ask for the batch-specific certificate of analysis for the finished product and check the lot number against your bottle. If the brand cannot produce either, treat the claim as unsupported.
The brand, in almost all cases. That is a structural conflict worth being aware of. What mitigates it is laboratory accreditation under ISO/IEC 17025, which requires impartial operation and independent assessment of competence [9]; blind retail sampling, which removes the brand's control over which sample is tested; and public batch databases that make selective publication difficult.
It is a meaningful marker, but read it carefully: accreditation is granted for specific tests rather than for a laboratory as a whole [9]. A lab may be accredited for heavy metals analysis and not for the potency method used on your product. A certificate stating the accreditation number lets you check the scope.
For commodity vitamins from an established retailer with simple supply chains, basic assurance is usually adequate. For higher-cost single actives where you cannot judge content by appearance, for botanicals and seaweed where contamination risk is inherent [10], and for anything bought from an anonymous marketplace listing, we would not buy without a finished-product certificate.
It should, but only if that panel was run. In the EU, maximum levels for lead, cadmium, mercury and arsenic in food including supplements are set by Commission Regulation (EU) 2023/915, with category-specific limits; Great Britain operates its own assimilated version of that legislation [10]. A certificate that omits heavy metals entirely has not tested for them — the absence of a result is not a pass.
Medical disclaimer
This article is for general information and does not constitute medical or regulatory advice. Certification programme details and regulatory requirements are summarised for consumer guidance, differ between Great Britain, Northern Ireland and the EU, and are subject to change — always check the relevant programme's own documentation and the current applicable legislation. Third-party testing verifies product content; it does not establish that a supplement is effective or suitable for any individual. Athletes subject to anti-doping rules should follow the guidance of their governing body and national anti-doping organisation, and no supplement can be guaranteed entirely free of contamination. 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. 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. Certification and regulatory positions correct at the time of publication and subject to change.
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