NHP Identity and Adulterant Testing: The Finished-Product Specs That Catch Undeclared Drugs

On 25 August 2026, Health Canada issued a Type I recall of two Twins Herbal liquids sold in Ontario. The reason was not a mislabelled dose or a stability failure. The products contained undeclared sildenafil, a prescription drug, inside something sold as a herbal remedy. It was the latest entry in a steady run of adulteration recalls that also includes a Magnum tadalafil recall and a standing Foreign Product Alert covering two dozen foreign health products with hidden drug ingredients.

For a licensed natural health product (NHP) company, these recalls point at the one control that decides whether an undeclared drug reaches your label: your finished-product specification and the identity and adulterant testing behind it. This article explains what that testing is, why Health Canada expects it, and how to build a specification that would catch sildenafil, tadalafil or a substituted botanical before a recall does.

Executive summary

Identity testing confirms that what is in your product is what your label says it is. Adulterant testing confirms that nothing else is there, in particular undeclared prescription drugs, unapproved drug analogues, or a cheaper botanical swapped in for the labelled one. Under the Natural Health Products Regulations and Health Canada's GUI-0158 good manufacturing practices guide, every NHP needs a written finished-product specification, and finished-product testing has to show the product meets it. A specification that lists only a potency assay will not catch an undeclared drug. A specification that pairs a validated identity method with a targeted adulterant screen will. The firms most exposed are those that rely on botanical or imported ingredients and qualify their suppliers on paper alone.

What are identity and adulterant testing?

Identity testing is the analytical confirmation that each medicinal ingredient in a natural health product is the substance named on the label, at the quantity claimed. Adulterant testing is the screening that confirms the product does not contain undeclared or prohibited substances, most importantly prescription drugs, unapproved drug analogues, heavy metals, or a substituted botanical. Identity answers the question, is it what we say it is. Adulterant testing answers the question, is anything here that should not be. Health Canada expects both, and a Type I recall is what happens when neither was done properly.

The two tests are not interchangeable. A potency assay can show that a labelled ingredient is present at the right amount and still miss a spiked drug sitting alongside it. An identity test can confirm the right botanical and say nothing about a hidden analogue. You need a specification that does both jobs, and a laboratory that can run the methods to do them.

Why Health Canada expects it

Because the law requires it. The Natural Health Products Regulations (SOR/2003-196) require a written specification for every natural health product and require testing against that specification before release. Health Canada's good manufacturing practices guide for natural health products, GUI-0158, sets out those specification and testing expectations in section 44 and the related quality provisions. The Quality of Natural Health Products Guide from the Natural and Non-prescription Health Products Directorate explains how to characterize a medicinal ingredient and when identity testing is required at the raw-material or finished-product stage. None of this is optional for a site licence holder.

How undeclared drugs get into herbal products

Adulteration almost always enters through the supply chain, not the finished line. A botanical or imported ingredient arrives with a certificate of analysis that the buyer never verifies. A contract manufacturer spikes a sexual-enhancement or weight-loss product to make it work. A supplier substitutes a cheaper species for an expensive one. Because sildenafil and tadalafil are colourless, close to tasteless and active at small doses, nothing about the finished product looks wrong. Only a targeted test finds them.

The classic adulterants are the phosphodiesterase type 5 inhibitors: sildenafil, vardenafil and tadalafil, plus a long tail of unapproved analogues designed to slip past routine tests. These substances carry real cardiovascular risk, especially when taken with nitrates, which is why Health Canada classes the recalls as Type I. The practical lesson is that a hidden drug is a supplier problem before it is a laboratory problem, so a rigorous supplier qualification programme is the first line of defence and identity plus adulterant testing is the second.

Building a finished-product specification that catches adulteration

A specification is only as good as the tests it names. Many NHP specifications list an identity test and an assay for the labelled ingredient and stop there. That set will confirm the product contains what the label claims, but it will not look for anything else. To catch adulteration you have to add a test whose whole purpose is to find what should not be present. The table below shows the tests a defensible specification includes and what each one proves.

The methods that find undeclared drugs

There is a recognized reference for this exact problem. USP General Chapter 2251, Screening for Undeclared Drugs and Drug Analogues, became official on 1 August 2016 and sets out analytical approaches for finding hidden drugs in supplements. It describes thin-layer chromatography with ultraviolet detection for a fast first pass, high-performance and ultra-high-performance liquid chromatography with ultraviolet detection for routine quantitation, and liquid chromatography coupled to mass spectrometry for detecting both known drugs and novel analogues. The method you choose depends on how much sensitivity and how much certainty you need.

A sensible programme layers these methods. Use a broad screen on incoming high-risk ingredients and on finished lots of any product in an adulteration-prone category, then confirm any signal with mass spectrometry against a reference standard. Document the screen in your specification so that a Health Canada inspector can see it was planned, not improvised after a complaint.

Identity testing by ingredient type

Identity is not one test. The right approach depends on the ingredient. A botanical needs species authentication, a mineral needs a compendial identity and assay, a probiotic needs strain-level identification, and a homeopathic medicine can only be identity-tested on the source material. Matching the method to the ingredient is where many specifications fall short.

What inspectors actually find

In practice, the gap that turns up during a Health Canada inspection is rarely a missing specification. It is a specification that does not connect to anything. A limit sits on a page with no test method behind it. A method exists but was never validated for that product matrix. Acceptance criteria do not match the shelf life on the label. A supplier certificate of analysis is treated as identity testing, when the site is expected to confirm identity itself. Each of these is straightforward to fix before an inspection and painful to explain during one.

The adulteration cases add a second pattern: a high-risk product in a category regulators watch, released on a specification that never included an adulterant screen. When an undeclared drug is later found, the company has no test result to show it looked, which reads as a control that was never designed rather than one that failed. Building the screen into the specification, and keeping the raw data, is what demonstrates due diligence when an inspector or a complaint puts the question to you.

When a result does come back out of specification or positive for an adulterant, the response matters as much as the finding. A defensible corrective and preventive action names the true root cause, whether it is a supplier, a method or a process step, extends the fix to every affected product, and verifies that the change worked. A CAPA that blames a single lot and closes quickly is the kind an inspector reopens. Treat each out-of-specification event as a question about the system, not just the batch.

NHP identity and adulterant testing checklist

Use this checklist to pressure-test your own specifications and release controls.

• Every product has a written finished-product specification with identity, quantity, purity and quality limits.
• Each medicinal ingredient has an identity test matched to its type, not a generic one.
• Adulteration-prone products (sexual enhancement, weight loss, sports, sleep) carry an undeclared drug screen in the specification.
• Screening methods reference USP 2251 or an equivalent validated method.
• Assay results are held to 80% to 120% of label, or the applicable compendial limit.
• Botanical ingredients are authenticated to species, and certificates of analysis are verified, not filed.
• Suppliers are risk-tiered and qualified, with periodic identity testing on incoming lots.
• Out-of-specification and adulteration results trigger an investigation and a documented CAPA.
• A recall procedure is written, rehearsed and supported by current distribution records.

Common mistakes

• Treating the certificate of analysis as proof. A supplier document is a starting point, not a release decision, and it is the exact place adulteration hides.
• Relying on a potency assay alone. An assay confirms the labelled ingredient and is blind to a spiked drug beside it.
• Skipping species authentication. Identity by label name is not identity by test, and botanical substitution is common.
• No adulterant screen on high-risk categories. Sexual-enhancement, weight-loss and sports products are the ones regulators watch, so they need the extra test.
• Using a screen that cannot see analogues. A method tied to a handful of reference standards misses the designer variants built to evade it.
• Never validating the in-house method. If you run your own test rather than a compendial one, it has to be validated and documented.

Frequently asked questions

Is identity testing required for every NHP in Canada?

Yes. The Natural Health Products Regulations require a written specification for every product, and the specification must address the identity of each medicinal ingredient. Health Canada's Quality of Natural Health Products Guide explains that identity may be verified at the raw-material stage, the finished-product stage, or both, depending on the ingredient and the process.

Do I have to test for undeclared drugs if I do not add them?

You are responsible for what leaves your facility, whether or not you intended it. Undeclared drugs usually enter through an ingredient or a contract manufacturer. For products in adulteration-prone categories, a screen is the only way to confirm a hidden drug did not arrive with a supplier, so it belongs in your specification even when your own formula is clean.

What is USP General Chapter 2251?

It is a United States Pharmacopeia general chapter titled Screening for Undeclared Drugs and Drug Analogues, official since 1 August 2016. It describes analytical approaches, from thin-layer chromatography to liquid chromatography with mass spectrometry, for detecting hidden drugs and their analogues in dietary supplements and similar products. It is a widely recognized reference for building an adulterant screen.

How is identity testing different for homeopathic medicines?

For homeopathic medicines, identity can only be tested on the source material, using the methods and criteria in a recognized homeopathic pharmacopoeia. Testing the final dilution is not meaningful because the active is present at very low levels, so the identity control moves upstream to the starting material.

What tolerance applies to the quantity of a medicinal ingredient?

Health Canada's guidance points to a tolerance of 80% to 120% of the label amount, or the limit set by the applicable pharmacopoeial standard where one exists. Your specification should state the limit you are holding the product to and the method used to measure it.

Can I rely on my supplier's certificate of analysis?

A certificate of analysis supports a release decision but does not replace it. Health Canada expects you to qualify suppliers and to verify incoming material against your own specification on a risk basis. For high-risk botanical or imported ingredients, that means periodic identity and adulterant testing rather than accepting the paperwork at face value.

How MFLRC can help

MF License and Regulatory Consultants helps NHP manufacturers and importers turn a thin specification into one that holds up under inspection. We design finished-product specifications, coordinate identity and adulterant test methods with accredited laboratories, and build risk-tiered quality control and testing programmes. We run supplier qualification, GUI-0158 gap assessments and mock audits, and we help you write and rehearse the recall procedure you hope you never use. If your product relies on botanical or imported ingredients, an identity and adulterant testing review is the fastest way to keep an undeclared-drug recall out of your future.

Conclusion

The adulteration recalls filling Health Canada's alerts are not a consumer story for licensed NHP companies. They are a quality-systems story. Every one of them traces back to a specification that did not test for the right thing and a supply chain that was trusted rather than verified. Identity testing proves what is in your product. Adulterant testing proves what should not be. Build both into your finished-product specification, qualify the suppliers behind your ingredients, and you protect not only your own licence but the reputation of the whole category you sell into.

Sources and references

• Health Canada, GUI-0158 good manufacturing practices guide for NHPs, sections 43 to 47 (specifications)
• Health Canada, Quality of Natural Health Products Guide (NNHPD)
• Natural Health Products Regulations, SOR/2003-196 (Justice Laws)
• Health Canada, Recalls and safety alerts, Twins Herbal products, undeclared sildenafil (RA-82524)
• United States Pharmacopeia, General Chapter 2251, Screening for Undeclared Drugs and Drug Analogues