How to read a supplement lab report
"Third-party tested" is printed on a lot of bottles. Far fewer brands actually show you the report. That gap — between claiming to test and letting you see the results — is the first thing worth noticing, because it tells you something before you've read a single number. A brand confident in its testing publishes it. A brand that merely wants the credibility of the phrase prints the words and hopes you won't ask to see the evidence. Once you know what a lab report actually contains, you'll understand why some companies are eager to show you and others aren't.
The good news: a certificate of analysis is genuinely easy to read once someone shows you the four things that matter. It's the single best tool you have for judging whether a supplement is what it claims — better than any front-of-pack slogan, better than brand reputation, better than price. Here's how to read one.
Identity: is it even the right ingredient?
The first check is the most basic, and it's more important than it sounds. Identity confirms that the ingredient in the bottle is actually what the label says — that your "magnesium bisglycinate" really is magnesium bisglycinate, and not a cheaper substitute wearing the same name on the front. It sounds like it should be a given. It isn't always, which is exactly why the test exists. Identity is the yes/no foundation: before you care how much is in there or how pure it is, you want confirmation that it's the right thing at all.
Potency: is the dose real?
Potency answers the question the front of the bottle is quietly hoping you'll take on faith: how much active ingredient is actually present, versus how much the label claims? It's usually expressed as a percentage of the label claim. What you want to see is a result at or slightly above 100% — meaning the batch delivers what it promises, or a touch more. A number well below 100% is the tell-tale sign of underdosing: a product that claims an impressive amount on the front but doesn't actually contain it. This single figure catches one of the most common ways supplements quietly cheat.
Heavy metals: is it safe?
The heavy-metals screen checks for lead, arsenic, cadmium, and mercury, measured against strict safety limits. What you're looking for here is a clear PASS. These elements exist in trace amounts across the natural world, so the goal isn't a fantasy of absolute zero — it's confirmation that they've been measured and sit safely below the established thresholds. A PASS means someone actually looked and the result was within safe bounds, which is precisely the assurance an untested product can't give you.
Microbials: is it clean?
The microbial panel checks for harmful bacteria, yeast, and mold — the contamination that can arise from how a product is manufactured and handled. Again, what you want is a PASS. It confirms the product was made cleanly and is stable, not harboring anything it shouldn't. It's the least glamorous of the four checks and one of the most reassuring, because it speaks to the basic hygiene of the whole operation behind the bottle.
The two details that separate real transparency from theater
Here's where you graduate from reading a report to judging whether it's worth anything. Two details separate a genuinely meaningful lab report from decorative "we tested it" theater.
First, the report should reference your specific lot number. Supplements are made in batches, and quality can vary between them, so a report needs to be tied to the exact production run your bottle came from. A generic certificate with no lot number — or one whose lot doesn't match your bottle — could be from any batch, including a flattering one produced specially to look good. The lot match is what anchors the proof to the product in your hand.
Second, the report should come from an independent lab, not the manufacturer's own bench. A company grading its own homework has an obvious conflict of interest; an outside lab with no stake in the result does not. "Third-party tested" is meaningful precisely because the third party is independent — remove that independence and the phrase is just words.
When a report has both — your lot number, and an independent lab — you're looking at real verification. When it's missing either, you're looking at something closer to reassurance-shaped decoration, and you should weight it accordingly.
Putting it to work
So the next time a bottle says "third-party tested," treat it as an invitation rather than a conclusion: ask to see the report, and when you find it, run the four checks and the two details. Identity confirmed, potency at or above 100%, heavy metals PASS, microbials PASS, tied to your lot, from an independent lab. That's the full picture, and it takes about two minutes once the layout is familiar. On every core+labs product page, the results are tied to the lot you're actually buying — no login, no email gate, just the numbers — because a report you can't see isn't proof of anything, and the whole reason to test is to let you check. Learn to read one lab report and you've learned to read them all — the four checks and two details are the same on every certificate you'll ever pick up, which turns a two-minute skill into a permanent advantage over every slogan on every front-of-pack you'll ever see.*
*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.