Supplements

The Pet Supplement Label Decoder

Updated July 28, 2026

MART PRODUCTION / Pexels

By Morgan Reyes

The Short Answer

Nobody reviews a pet supplement for potency, purity or effectiveness before it goes on sale. The FDA's only guidance document written specifically for companion-animal supplements was withdrawn on 20 February 2020 and its replacement expressly does not cover supplements.

And when someone does test them, a meaningful share fail. The most uncomfortable number belongs to the industry itself: when the trade association tested 87 brands, 28% did not contain what was claimed.

So the label is the only thing you have, which makes reading it a real skill. There are five lines that matter and they are below, in the order to read them.

So who actually checks this bottle before it reaches the shelf?

Nobody, in the sense you would want.

There is no pre-market approval for a pet supplement. The product is regulated as animal food, or as an unapproved new animal drug if its label makes a treatment claim, which is why bottles are written so carefully around what they promise.

The FDA once had a policy document written specifically for this category: Compliance Policy Guide 690.100, "Nutritional Supplements for Companion Animals," issued in 1980 and revised in 1995. It was formally withdrawn on 20 February 2020. Its successor, CPG 690.150, covers therapeutic diets for dogs and cats and states that it does not apply to supplements.

Which leaves post-market enforcement. The FDA's adulteration standard turns on whether a product contains "significantly more or significantly less" than its label declares, and that assessment happens after the product is on sale, usually after somebody complains.

None of this makes pet supplements uniquely dangerous. It makes them unverified, which is a different problem and the reason this page exists. The fuller regulatory picture, including what a statutory category would change, belongs to its own guide, and that one is not built yet.

When someone has tested these, what did they find?

Every time somebody has tested pet supplements against their own labels, a meaningful share failed, including when the industry tested itself.

In plain terms: this is not a story about a few bad actors getting caught. It is the base rate.

Two things in that table deserve pointing at.

The 28% figure is the trade association's own. NASC ran that testing and the number came out through Associated Press reporting. An industry body publishing a result that unflattering is worth more than a critic publishing the same number, and it is the single most citable fact on this topic.

Failure runs in both directions. The 2019 Boswellia study found products averaging 173% of their label claim, and one at 224%. Over-delivery is not a bonus: it means the manufacturing was not controlled, and for an ingredient with a dose-dependent effect it means you do not know what you gave your animal.

And here is what nobody says: there is no large, recent, independent, multi-category test of pet supplements. The 2013 round is the most recent broad consumer testing we could verify, and its product-level detail sits behind a paywall. If a page implies this question has been settled by ongoing surveillance, it is overstating what exists.

The Five Lines: what to read, in order

This is the part to actually use. Five lines, in this order, and the last two take five seconds each.

1. The active-ingredient line, and the unit it is quoted in

Find the active ingredient, then find out whether that number is per chew or per dose. These are different numbers and packages move between them freely.

Work an example. A bottle says 300 mg glucosamine per chew, and the feeding directions say 2 chews daily for your dog's weight. Your actual daily dose is 600 mg. Another bottle says 500 mg per serving and defines a serving as 2 chews, so it is 250 mg per chew and 500 mg daily. The first bottle looked weaker per chew and delivers more.

The scoop trap. Powders are often quoted per scoop, and a scoop is a volume, not a dose. Two scoops of differently-milled powder do not contain the same mass. If a label gives you only scoops and no milligrams, you cannot compare it to anything.

2. "Proprietary blend"

If the active you are paying for sits inside a proprietary blend with no per-ingredient milligram figure, treat the dose as unknown.

A blend discloses one total weight for several ingredients. It is legal, and it is not automatically dishonest. But it is unverifiable by design, and the cheapest ingredients in a blend can legitimately make up almost all of that total weight.

The wording to look for is a bracketed group with a single milligram figure after it, rather than a figure against each named ingredient.

3. The NASC seal

The seal is about process, and that is worth something. It is not about whether the product works.

To carry it, a company must maintain documented quality-control procedures, run an adverse-event reporting and complaint system, comply with FDA labelling guidance including recommended caution statements, submit to random independent lab testing against label claim, and pass an independent facility audit.

That is a genuinely higher bar than nothing, and on a shelf where nobody checks anything before sale, it is the strongest available signal.

Now the part that is rarely stated. NASC does not publish how often audits happen, how many products are tested, what the pass threshold is, or what happens to a company whose product fails. A two-year audit cycle is widely reported by trade press and member companies, but not on NASC's own public pages, so treat that specific number as second-hand.

4. The lot number and the expiry date

A missing lot number is disqualifying. Not a warning sign, disqualifying.

The lot number is the difference between "I think my dog reacted to something" and a report that somebody can act on. Without it, neither the manufacturer nor a regulator can identify what your animal actually consumed.

Both are usually printed rather than part of the label design, so check the crimp at the top of a pouch, the base of a tub, or a separate sticker. If neither appears anywhere, put it back.

5. Who to contact, and whether the claim is checkable

A named formulator you can look up beats "veterinarian recommended" with no name attached. A real postal address and phone number beat a web form.

And if you want to verify content, ask for a certificate of analysis for your lot number, on the finished product. That qualifier matters: the 2020 hemp study requested certificates from 22 companies and found that three supplied raw-material certificates instead of final-product ones, which describe an ingredient before manufacturing rather than the bottle in your hand.

A generic certificate posted on a website is a marketing asset. One matching your lot is evidence.

What this label cannot tell you

Is any of this about to change?

Not yet, and the usual reporting overstates it.

NASC has drafted an Animal Health Supplement Act and is lobbying for it, with the aim of creating a statutory category for animal supplements, which does not currently exist.

As of 28 July 2026, no bill of that name appears in the federal legislative record. We checked the government's own full-text legislative index across all collections and got zero results, then ran a control query on a comparable act and got several hundred, so the zero is a real zero rather than a broken search.

So: proposed industry legislation, not pending law. Anybody describing it as "before Congress" is ahead of the facts.

FAQ

Does the FDA approve pet supplements?

No. No pre-market review of potency, purity or effectiveness. See the section above for what replaced the FDA's withdrawn guidance, and what it does not cover.

Does the NASC seal mean a supplement works?

No. It means documented processes, adverse-event reporting, compliant labelling, random independent testing against label claim, and a facility audit. Real requirements, and none of them about efficacy.

How often do pet supplements fail testing?

Often enough to expect it. The industry's own trade body found 28% of 87 brands did not contain what was claimed, and a 2020 study found only 10 of 29 hemp products within 90 to 110% of label.

What does "proprietary blend" mean?

Several ingredients under one total weight, with no per-ingredient breakdown. Legal, unverifiable, and a reason to treat the dose as unknown.

Is a certificate of analysis proof?

Only for the finished product and your lot number. Three of 22 companies in the 2020 study supplied raw-material certificates instead.

Is the law about to change?

There is a drafted industry bill and an active lobbying effort, and no bill in the record. See above.

Bottom line: nothing verifies a pet supplement before it ships, the FDA's only guidance written for the category was withdrawn in 2020, and every time anybody has tested these products against their own labels a meaningful share failed, including the 28% of 87 brands found by the industry's own trade association. That leaves the label, so read five lines in order: the active ingredient and whether the figure is per chew or per dose, whether the actives hide inside a proprietary blend, whether the NASC seal is present and what it does and does not cover, whether a lot number exists at all, and whether there is a named human being and a lot-specific certificate behind the claim. A missing lot number is the one hard stop.

Keep reading

• Read Any Pet Food Label in 60 Seconds. The same skill on a much more regulated shelf, including the dry-matter conversion.
• What Actually Counts as a "By-Product" in Pet Food. What AAFCO's ingredient definitions actually say.
• Grain-Free Dog Food: What the Science Actually Says. How to read an open scientific question honestly, including who funded which study.

The obvious next question, whether a given ingredient has any evidence behind it, needs its own page per ingredient. Those are planned and not built, so this guide deliberately stops at whether the bottle contains what it claims.

A Note on Scope

This guide explains how pet supplements are regulated and how to read one's label. It is not veterinary advice, no veterinarian reviewed it, and it recommends no product. It does not tell you whether your animal needs a supplement, and for most animals eating a complete and balanced diet the answer is that they do not.

Talk to your vet before starting any supplement, particularly if your animal takes medication, since interactions are real and a label will not warn you about them. Never give a human supplement to an animal on the assumption that the dose scales. If your pet becomes unwell after starting a supplement, stop it, keep the packaging with its lot number, and call your vet.

Sources

• FDA, Compliance Policy Guide 690.100, "Nutritional Supplements for Companion Animals," withdrawn 20 February 2020. Read via an archived capture; fda.gov blocks automated requests, and the live page is the citation.
• FDA, animal food and feed product regulation. How a supplement is classified, and the unapproved-new-animal-drug boundary.
• Wakshlag et al., "Cannabinoid, terpene, and heavy metal analysis of 29 over-the-counter commercial veterinary hemp supplements," Veterinary Medicine: Research and Reports, 2020. The 10-of-29 figure, the 0 to 154% range, the heavy metals, and the raw-material certificate finding.
• Reichling et al. on canine Boswellia products, BMC Veterinary Research, 2019. The 173% average and the 114 to 224% range, showing failure in the over-delivery direction.
• govinfo full-text search API. Used on 28 July 2026 to establish that no Animal Health Supplement Act appears in the federal legislative record, with a control query to confirm the index was working.