Third party tested supplements are only as strong as the certificate behind them, and a certificate covers four separate questions: identity, potency, heavy metals and microbes. A single panel rarely answers all four, which is why two bottles with the same label can sit at very different levels of verification.
The four questions behind third party tested supplements
Identity asks whether the bottle holds what the front says. Potency asks how much, measured against a stated figure. Heavy metals ask about lead, arsenic, cadmium and mercury. Microbes ask about what grew during handling. Four tests, four methods, four line items on an invoice.
A certificate listing only potency is real and still incomplete. You're allowed to read it that way.
Working through the zinc L-carnosine example
Take zinc L-carnosine. Each capsule carries 75 mg of the chelated compound, and the bottle holds 120 capsules. The compound question and the element question are not the same, and a potency panel that reports one while the label implies the other is where people misread a spec sheet.
Identity, potency, heavy metals and microbes each need their own assay. Ask which ran. A brand that tested metals on one batch and potency on another hasn't covered the bottle in your hand.
Three things to ask before you buy
Which batch was tested. Which lab ran it. Which four questions the panel answers. That's the whole script, and it takes one email.
You'll get one of two replies. The first attaches a dated certificate naming the lab and the batch number. The second sends a marketing page with no batch on it anywhere. The second isn't proof of a bad product. It's proof of nothing, and that's a different thing you're allowed to weigh.
Testing is voluntary across most of the market, so a missing certificate isn't evidence of a problem. It's an absence of evidence, and you get to decide how much that costs you.
Ask about the elemental number too, since it's the one people skip. Whether a bottle shows total zinc or elemental zinc changes the whole comparison, and 15 mg of one is not 15 mg of the other.
The part brands are slow to say
Verification lives on a spectrum. Running four assays on every production run costs real money, and that cost goes somewhere. Cheap bottles print badges. Serious ones print batch numbers. A badge claims a process happened once. A certificate speaks for one specific run, which is the only claim worth having.
Consider a week in your own kitchen. You bought a bottle in March, it sits in a cupboard, and by June you're still going. The certificate that mattered was for the batch in that bottle, not for a run that happened two years earlier. Ask how often they panel. A brand that tests every run can speak for yours, and one that tested once cannot.
Brands that test seriously reply in days and don't make you ask twice. Slower replies tell you where verification sits in their list of priorities.
Keep the certificate with the bottle. It's a one page document, and it's the only thing standing between a label claim and something you can actually check. Photograph it for the batch you're using now, since the next bottle is a different run with a different set of numbers behind it.
Frequently asked questions
What does a certificate of analysis cover?Show answerHide answer
Whatever assays were ordered. Ask which were run before assuming anything.
Is testing legally required?Show answerHide answer
Verification is voluntary in most of the market, which is why brands differ so much.
What should I ask a brand?Show answerHide answer
Which batch was tested, by which lab, and for which four things.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
