How to read a certificate of analysis
A certificate of analysis is a lab report for one batch: check that its lot number matches your bottle, then read identity, potency against the label, and purity limits.
In plain words
- A certificate of analysis is a lab report for one batch of a supplement.
- Check that its batch number matches the number on your bottle.
- It should show how much of the main ingredient is really inside.
- It should show tests for metals, germs and other things that should not be there.
- A report from an outside lab counts for more than one made by the brand itself.
What is a certificate of analysis?
A certificate of analysis, or COA, is a lab report tied to one production batch, also called a lot. It states what testing found: whether the ingredient is what the label says, how much is actually there, and whether anything harmful came along with it.
Federal manufacturing rules require supplement makers to set specifications for identity, purity, strength and composition, and to check that they are met [4]. The COA is where a brand shows that data, or does not.
The most useful question you can ask any supplement company is simple: can I see the COA for this lot? How readily they answer tells you a lot.
Identity: is it what the label says?
Identity testing confirms that the material in the capsule is the ingredient on the label, not a cheaper substitute or an adulterant. Labs use methods such as HPLC (high-performance liquid chromatography), FTIR (infrared spectroscopy) or DNA methods for botanicals. This is the check that catches a bottle labeled as one herb that contains another, or mostly filler.
Potency: how much is really in there?
The assay reports the measured amount of the active compound against the label claim, usually as a percentage. You want results close to 100 percent of claim. A result far below means you are paying for a dose you are not getting; a missing number means no one checked. A proprietary blend with no assay for each ingredient keeps that number hidden.
Purity: what should not be there?
This section matters most and is the one most often skipped. It should cover three groups of contaminants.
- Heavy metals: lead, arsenic, cadmium and mercury, each with a stated limit and a result.
- Microbes: total aerobic count, yeast and mold, and the absence of pathogens such as E. coli and Salmonella.
- Residual solvents and pesticides: left over from extraction or farming, especially relevant for botanicals and concentrates.
How strict should the limits be?
Published standards give you a yardstick. The United States Pharmacopeia sets limits for elemental impurities in drug products and for elemental contaminants in dietary supplements [1][2], and California's Proposition 65 sets a maximum allowable dose level for lead of 0.5 micrograms a day [3].
Results are often written as below LOQ or below LOD: below the limit of quantification, or of detection. That means the contaminant was not found above the level the instrument can reliably measure. That is good, but check that the stated limit is low enough to mean something. Not detected is only as strong as the threshold behind it.
Who ran the test?
A COA from an outside, ISO/IEC 17025-accredited lab carries more weight than one produced in-house by the manufacturer. Seals from independent testing organizations, such as USP Verified or NSF certification, show that a product passed that organization's checks, and they sit on top of the FDA's baseline manufacturing rules [4][5].
A seal tells you that testing happened. Reading the results is still on you, and a certificate covers only the lot it names.
A five-point COA checklist
Certificates that brands publish or provide, together with their manufacturing certifications, are what we rely on when choosing which brands to carry. You can run the same check on any bottle.
| Check | What good looks like |
|---|---|
| Lot match | The COA names the exact batch number printed on your bottle, not a generic one |
| Who tested | An accredited outside lab rather than the brand's own |
| Heavy metals | All four (lead, arsenic, cadmium, mercury), each with a limit and a result |
| Identity and potency | Both present: what it is, and how much |
| Access | The brand shares it when asked; if it will not, take that as the result |
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Common questions
Where do I find a certificate of analysis?
Some brands publish them online by lot number; others send them on request. Ask for the COA that matches the lot number printed on your bottle.
Does a quality seal replace the COA?
No. A seal shows that testing happened. The certificate shows what the testing found for one specific lot.
What does "not detected" mean on a COA?
That the contaminant was not found above the lab's limit of detection. Check that the stated limit is low enough to be meaningful.