Structure/Function Claims Testing Requirements

"Supports immune health." "Promotes restful sleep." "Maintains healthy blood sugar levels." Structure/function claims are the primary way supplement brands communicate what their products do without crossing into drug territory. But these claims come with legal obligations, and the FDA requires substantiation -- meaning you need data to back them up. Testing is a critical part of that substantiation file. Here is what the FDA expects, what testing is required versus recommended, and how to build a defense that holds up under scrutiny.

What a structure/function claim is under the law

Under DSHEA and FDA guidance, a structure/function claim describes how a dietary ingredient affects the structure or function of the human body. It cannot claim to diagnose, cure, mitigate, treat, or prevent a disease. The difference between a structure/function claim and a disease claim can be subtle, but getting it wrong can make your product an unapproved new drug in the FDA's eyes.

The four types of acceptable statements on supplement labels:

1. Structure/function claims: "Calcium builds strong bones." "Fiber maintains bowel regularity."
2. Claims of general well-being: "Promotes overall health." "Supports wellness."
3. Nutrient deficiency claims: "Contains vitamin C, which supports immune function." (Must disclose prevalence of the deficiency in the US.)
4. Mechanism of action statements: "Antioxidants neutralize free radicals."

Any statement that explicitly or implicitly ties the product to a disease state is a disease claim and not permitted for supplements. "Supports healthy cholesterol" is a structure/function claim. "Lowers cholesterol" is a disease claim. "For use by arthritis sufferers" is a disease claim. "Supports joint comfort" is a structure/function claim.

What the FDA requires for claim substantiation

The FDA's position, articulated in guidance documents and enforcement actions, is that structure/function claims must be substantiated by "competent and reliable scientific evidence." The FDA does not define a specific formula for what constitutes substantiation, which gives the agency flexibility in enforcement but leaves brands without a clear checklist.

In practice, a strong substantiation file for a structure/function claim includes:

1. Identity and potency testing confirming the product contains the dietary ingredient at the labeled amount. A claim that your product "supports healthy blood pressure" because it contains magnesium is not substantiated if testing shows your product contains 50 mg per serving when studies supporting the claim used 300 mg. Your label claim must match both the studied dose and what is actually in the product.

2. Evidence that the dietary ingredient at the labeled dose has the claimed effect. This can include human clinical trials, meta-analyses, animal studies, in vitro data, and traditional use evidence. The FDA expects the totality of evidence to support the claim. A single small pilot study is weaker than multiple randomized controlled trials. Published, peer-reviewed research from reputable journals carries more weight than unpublished manufacturer studies.

3. Documentation that the mechanism is biologically plausible. How does the ingredient produce the claimed effect? This is typically supported through biochemical and physiological research.

4. The FDA disclaimer on the label: "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."

5. FDA notification within 30 days of first marketing the product with the claim. The notification must include the exact text of the claim, the name and address of the manufacturer or distributor, and the name of the dietary ingredient.

💡 Note

The single most common testing gap in structure/function claim substantiation is potency. A brand has literature showing that 500 mg of an herb supports a health endpoint, and the label says 500 mg, but the brand never tested the finished product to confirm it actually contains 500 mg. The claim file is undermined by the failure to prove the product delivers the studied dose. Potency testing by HPLC or ICP-MS closes this gap.

The testing that is required (not optional)

Even without a structure/function claim, federal regulations require specific testing. When you add a claim, the testing stakes are higher because the FDA and plaintiff's attorneys will look at your testing records to see whether you can back up what the label says.

Testing required under 21 CFR 111 regardless of whether you make claims:

• Identity testing (111.70(e)): At minimum one identity test on every dietary ingredient lot before use. Confirms the ingredient is what you think it is.
• Finished product testing (111.75(a)(2)): Verify that each finished batch meets specifications for identity, purity, strength, and composition.
• Contaminant testing (111.75(c)): Test for contaminants that may be introduced during manufacturing or that are known to be associated with your ingredients.

Testing that becomes especially important when you make structure/function claims:

• Potency testing on every finished product batch. If your claim is based on a specific dose, you must confirm the dose is present. A Supplement Facts panel listing 500 mg of magnesium with testing showing 420 mg makes your claim objectively inaccurate and your product potentially misbranded.
• Stability testing to support the labeled dose through the expiration date. If your product degrades from 500 mg to 350 mg of active ingredient by the expiration date, your claim is not substantiated for the product as sold throughout its shelf life.

For the full testing requirement framework, see our 21 CFR 111 testing requirements guide and our shelf-life stability testing guide.

Building a substantiation file that holds up

A substantiation file is the collection of documents and data that supports your structure/function claim. Think of it as the folder you would hand to a regulator or opposing counsel if challenged. A strong file includes:

Section 1: Product testing data

• COAs for identity and potency testing on each finished product batch
• Stability data showing potency at labeled levels through expiration
• Third-party testing from ISO 17025 accredited labs, not in-house screening

Section 2: Scientific literature

• Published studies supporting the claimed effect at the labeled dose
• Peer-reviewed research from recognized journals
• Meta-analyses and systematic reviews if available
• Standardized extracts or ingredient forms that match what is in your product

Section 3: Ingredient specifications

• Botanical authentication reports confirming species identity
• Marker compound standardization data for herbal ingredients
• Documentation that your ingredient form matches the studied form (e.g., magnesium citrate in studies must match the magnesium citrate in your product -- magnesium oxide is not a substitute)

Section 4: Quality documentation

• GMP compliance evidence (NSF registration or equivalent)
• Supplier qualification records
• Certificate of Analysis from ingredient suppliers with verification

Section 5: Regulatory documentation

• FDA structure/function claim notification acknowledgment
• Label copy showing the exact claim language and disclaimer
• Legal review confirming claims are not disease claims

What happens when the FDA challenges your claims

The FDA challenges structure/function claims through Warning Letters when it believes claims are unsubstantiated or are actually disease claims. The Warning Letter will typically state that the claims make the product an unapproved new drug or a misbranded food. Consequences can include product recall, injunction, and reputational damage.

FTC challenges also occur. The Federal Trade Commission regulates supplement advertising, and it has pursued supplement companies for deceptive advertising when structure/function claims were not adequately substantiated. FTC actions can result in consent decrees, fines, and requirements to provide refunds to consumers.

Class-action litigation is increasingly common. Plaintiff's firms file lawsuits against supplement brands alleging that structure/function claims are false or misleading because the product does not contain the claimed ingredient at the labeled amount (discovered through independent testing) or the scientific substantiation is weak. These lawsuits often settle for significant amounts.

In all three scenarios -- FDA, FTC, or litigation -- your testing data and substantiation file are your defense. A strong substantiation file backed by ISO 17025 accredited laboratory data is the difference between resolving a challenge quickly and spending years in enforcement or litigation.

Common mistakes in claim substantiation

Mistake 1: Using the wrong form of an ingredient. Studies showing magnesium glycinate supports sleep do not substantiate a sleep claim for a product containing magnesium oxide, which has different bioavailability and was not studied for sleep endpoints. Ingredient form matters.

Mistake 2: Citing a dose different from what is in the product. A study using 1,000 mg per day of an herb does not substantiate a claim for a product containing 200 mg. Your product must deliver the dose that was studied.

Mistake 3: No testing to confirm the labeled dose is actually present. If you claim 500 mg of an amino acid per serving but never test to confirm the 500 mg is there, your substantiation file has an unfillable hole. Testing data is the bridge between the literature and your product.

Mistake 4: Relying on supplier COAs without verification. A supplier COA saying the raw material contains 95% of the active compound is not sufficient. You must verify through your own (or your contract lab's) testing. This is both a GMP requirement (111.70(e)) and a substantiation requirement.

Mistake 5: Making claims for proprietary blends without specifying individual ingredient amounts. If your label lists a "proprietary blend" of 500 mg containing five ingredients but does not disclose individual amounts, the FDA may consider your claims unsubstantiated because the consumer (and the agency) cannot determine the dose of each ingredient.

For help comparing labs that can support your claim substantiation testing, see our lab comparison guide.

Quick Reference

Lab Category Matching

Real Methods Explained

What Sample to Send

Finished product in final packaging, following the lab's chain-of-custody procedure. For claim substantiation testing that will go into your claims file, send retain samples from multiple batches (at least 3 non-consecutive lots) to demonstrate batch-to-batch consistency of the claimed ingredient level. Typical sample quantity: 50-100 g or 10-20 capsules/tablets per test. Confirm with the lab.

Expected Turnaround Time

Accreditation Notes

All testing used in your substantiation file should be performed by an ISO/IEC 17025 accredited laboratory. If your claims are ever challenged (by FDA, FTC, or in litigation), your testing data will be scrutinized. Results from non-accredited laboratories will be challenged and may be excluded or given less weight. The lab's scope of accreditation must include the specific methods used for your testing. For botanical identity, ensure the lab's scope includes HPTLC or HPLC for botanical authentication.

Price Ranges

Country/Region Targeting

For US market products, FDA and FTC substantiation standards apply. For Canada, Health Canada requires pre-market licensing (NPN) with claims supported by evidence reviewed during the application. Claims for NHPs in Canada are generally more restricted than US structure/function claims. For the EU, claims on food supplements are regulated under Regulation (EC) No 1924/2006, which requires authorized health claims from the EU Register. Unauthorized claims are prohibited. Structure/function claims as they exist in the US do not have a direct equivalent in the EU. Always review claims compliance for each target market separately.

FAQ

Q: What level of evidence does the FDA require for structure/function claims?

The FDA requires "competent and reliable scientific evidence" to substantiate structure/function claims but does not specify the number or type of studies required. In practice, the FTC standard for advertising claims is often applied: claims should be supported by at least one well-designed human clinical trial that is consistent with the totality of evidence. The strength of substantiation should be proportional to the strength of the claim. A claim that an ingredient "supports" a function requires less evidence than a claim that it "improves" or "enhances" that function. More specific and stronger claims require stronger evidence. Published, peer-reviewed research carries more weight than unpublished or manufacturer-funded studies.

Q: Do I need to test every batch for potency if I make a structure/function claim?

Under 21 CFR 111.75(a)(2), you must verify that each finished product batch meets specifications for strength (potency). This means while you may use a skip-lot testing program if scientifically justified, the FDA expects batch-level verification. If your claim is based on a specific dose, and you are not testing every batch's potency, you risk an unsubstantiated claim. The safest and most common approach is to test every batch for the analytes that support your claim. For ingredients where potency is stable and well-characterized, a reduced testing frequency may be justifiable with data, but the burden of justification is on you.

Q: What is the difference between a structure/function claim and a health claim?

A structure/function claim describes how a dietary ingredient affects the structure or function of the body ("calcium builds strong bones"). A health claim links a dietary ingredient to a disease or health-related condition and must be authorized by the FDA based on significant scientific agreement ("calcium may reduce the risk of osteoporosis"). Health claims are authorized by the FDA through a petition process, are subject to strict wording requirements, and require a high level of scientific evidence. Structure/function claims do not require FDA pre-authorization but still require substantiation. The practical difference: you can make structure/function claims without FDA approval. You cannot make health claims unless they are FDA-authorized.

Q: Can I make structure/function claims for a proprietary blend?

Yes, but it is riskier. If your label lists a proprietary blend without disclosing individual ingredient amounts, the FDA may consider your claims unsubstantiated because neither the consumer nor the agency can determine the dose of each ingredient. Furthermore, class-action plaintiffs frequently target proprietary blend claims, arguing that the undisclosed amounts prevent consumers from knowing whether the product contains efficacious doses. If you use a proprietary blend: (1) ensure every ingredient in the blend is tested for identity, (2) test the total blend for potency, (3) have a strong substantiation file for the blend as a whole, and (4) consider disclosing individual amounts to reduce risk.

Q: How long do I need to keep my substantiation files?

There is no specific regulatory retention period for substantiation files, but they should be kept for as long as you market the product with the claim, plus a reasonable period after discontinuation. Given that the statute of limitations for FTC enforcement is generally three to five years (and can be longer under certain circumstances), and class-action lawsuits can be filed years after purchase, retaining substantiation files for at least five years after the last product sale is prudent. Testing records under 21 CFR 111 must be retained for one year past the shelf-life date (if shelf life is supported by stability data) or two years from distribution for products without stability-supported expiration dates. These are cumulative with any longer retention periods in your internal policies.

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