How can you tell if a peptide vendor is legitimate?

How can a buyer independently check whether a manufacturer is FDA-registered?

This is checkable, and it does not require taking a seller's word for it. FDA maintains the Drug Establishments Current Registration Site, a public database of currently registered establishments that manufacture, prepare, compound or process drugs distributed or offered for import in the US [4]. It includes a searchable registration tool, though it does not cover 503B outsourcing facilities or wholesale distributors, which sit in separate systems.

FDA's own guidance on 503A bulk substances tells compounders directly to know your bulks supplier [3]. That instruction implies the agency expects buyers, not only regulators, to do this checking rather than rely on assurances.

What does a certificate of analysis actually have to be backed by?

A certificate of analysis is not self-certifying paperwork. FDA's guidance on analytical procedures and methods validation requires that the methods behind a certificate be validated for suitability, covering specificity, accuracy, precision and detection limit, against the ICH Q2(R1) standard [5]. The same guidance requires that reference standards used in that testing carry their own qualification reports and certificates [5].

In practice this means a certificate is only as trustworthy as the validated method and reference standard behind it. A document that does not disclose its testing method, or that cannot be traced to a real laboratory using a qualified reference standard, does not meet this bar, whatever it is titled.

Does having documentation, or claiming 'research use only', change how the FDA treats a seller?

No, and two separate 2026 warning letters make this explicit. One letter found that a seller's products, including semaglutide and tesamorelin, were unapproved new drugs despite research use only and not for human consumption labelling, because the company's own website described human therapeutic effects [6]. A second letter, to a different seller, reached the same conclusion for different products, citing evidence obtained from the seller's own product labelling [7].

Neither letter cited a missing certificate of analysis or an unregistered facility as the basis for action. The violation in both cases was the seller's own marketing language, independent of what paperwork accompanied the product. Documentation quality and legal status are two separate questions: a seller can have excellent paperwork and still be selling an unapproved drug, and Import Alert 66-41 gives the agency a border-enforcement tool that applies regardless of a shipment's accompanying documents [8].

Is there an EU-side equivalent check?

Yes. The European Medicines Agency operates EudraGMDP, the EU database on manufacturing, import and wholesale-distribution authorisations and good manufacturing and distribution practice certificates [9]. It has been publicly searchable since 2011 and includes non-compliance statements alongside valid certificates.

As with FDA's registration site, this lets a buyer check a manufacturer's actual authorisation and compliance status directly, rather than relying on a seller's claims.

What happens when a nominated substance lacks sufficient documentation at the regulatory level?

FDA's own review process for 503A bulk substance nominations shows what insufficient documentation looks like at the regulatory level. Its evaluation guidance states that many early nominations were not for substances used as active pharmaceutical ingredients, or did not include sufficient information for FDA to evaluate the nominated substance [10]. The agency subsequently reopened the process to request more detailed supporting information.

This is a useful reference point. If FDA itself, with the authority to demand data, rejects nominations for insufficient documentation, a consumer relying on a vendor's self-supplied paperwork faces the same evidentiary problem with far less power to demand more.

What would change this answer

An FDA or USP document specifically defining minimum certificate-of-analysis disclosure standards for research-use-only chemicals, rather than regulated pharmaceutical ingredients, would fill this answer's largest gap. An EU-level guidance addressing documentation standards for research-use substances outside the medicines framework would fill the parallel gap there. A published enforcement action that cites a missing or fraudulent certificate itself, rather than intended-use language alone, would sharpen the claim that documentation and legal status are separate questions.