Open two supplement brands' websites and you will notice a strange difference. One brand publishes its lab results openly — certificates of analysis, batch numbers, the name of the laboratory that did the testing. The other brand says "third-party tested" in large letters and shows you nothing at all. Both claims sound reassuring. Only one of them can be checked.

Testing is not a single thing. A certificate of analysis is a lab report for one specific batch: it says what was tested, what was found, and whether the result passed. A brand that publishes these documents is letting you verify its claims batch by batch. A brand that only says "tested" without showing a document is asking you to take its word for it — and in an industry where the word is the cheapest thing on the label, that is a meaningful difference.

There are honest reasons a brand might not publish everything. Lab reports contain commercial details, testing is expensive, and smaller brands may test less often than large ones.…