It appears on thousands of labels, and no regulation defines it. Here’s how to tell a verified credential from a printed phrase.
The phrase itself is unregulated. In the U.S., supplements reach shelves without pre-market approval; the FDA acts after a product is on sale, not before. No rule defines who may print “third-party tested” on a label. On its own, the phrase tells you a test happened somewhere, at some point, on something — not what was tested, which lab did it, or what the results were.
Certification marks are a different thing. A mark like NSF, USP Verified or Informed Sport is a license from an independent organization with published standards. The certifier tests the product before the mark goes on, then keeps auditing it for as long as the license lasts, with periodic retesting and facility inspections. The major programs all verify the same three things: identity, meaning the bottle contains what the label names; potency, meaning the dose matches what the label states; and contaminants, meaning heavy metals, microbes and solvents stay within limits.
A certification mark is a credential you can verify. “Third-party tested,” by itself, is only a claim.
The programs differ at the edges. Informed Sport screens every single batch for substances banned in competitive sport, which is why athletes look for that mark specifically. NSF and USP audit on a schedule rather than batch by batch. All three publish exactly what they test for, so the mark on a bottle can be traced to a written standard.
Certification is voluntary, and it costs money. Programs charge for the testing, the auditing and the license itself. That context matters when a mark is absent: a missing mark does not prove a problem, but a present one represents ongoing outside scrutiny that the company chose and paid for. It is why our Testing score treats a verified mark and a bare “tested” claim so differently.
What certification doesn’t tell you is whether the ingredient does anything. A certified product can deliver a perfectly verified dose of something with weak evidence behind it. Testing answers “is it what it says it is?” Evidence answers “does it do anything?”
Every real mark is searchable. NSF, USP and Informed Sport all keep public databases of the products they certify, searchable by product name. A genuine mark takes about a minute to confirm. A mark that doesn’t appear in the certifier’s own listings is a gap worth knowing about, and it’s one of the first things our reports check.