Accepted answer
The question to ask is not whether a vendor is good but what evidence exists, of what kind, about which lots, from whom. Reputation is a compression of that evidence and it compresses badly.
Lot-to-lot content variation of nine per cent between two nominally identical lots, both within a stated specification, is the single most common finding in independent testing and the least discussed. It is not fraud; it is the consequence of a fill process controlled to a tolerance rather than to a target. It is also the reason a per-lot content assay is worth more than a per-supplier reputation.
Certificate red flags and what each implies
| Observation | Implication | How to check |
|---|
| Lot number not on the vial | Certificate cannot be tied to your material | Photograph vial and certificate together |
| No method section | The number is not reproducible | Request column, gradient, wavelength |
| Purity to two decimals, no chromatogram | False precision | Request the trace |
| Test date before manufacture date | Certificate belongs to a different lot | Compare dates |
| Identical figures across lots | One certificate reused | Compare two lots side by side |
| “Sterile filtered” with no sterility test | Process claim substituted for a result | Ask for the sterility report |
What a verification listing at VendorInvestigate or a rating at PeptideMeter actually evidences is that some process was applied — which is more than nothing and considerably less than an audit. The useful question is what the process consists of and whether its inputs are independently obtained samples or vendor-supplied ones.
Regulatory positions on personal importation are published: the relevant frameworks are the US FDA’s personal importation policy in its Regulatory Procedures Manual, the UK MHRA’s guidance on importing medicines for personal use, and the equivalent national provisions in the EU member states and Australia’s Therapeutic Goods Administration personal importation scheme. They differ materially from each other.
One qualification: independent testing tells you about the vial you sent. It tells you about the vial you kept only under an assumption of homogeneity that nobody has tested.
If a supplier will not send you a lot-specific certificate before you order, you have learned something useful at zero cost.
edited 25 Oct 2025 by Dr_Colm_Fitzhenry — added a caveat about sampling
5This should probably be in the site help pages rather than buried in an answer. – vialroom 5 months ago 6Good answer, but the confidence interval in the cited trial is wider than implied. – net_peptide 7 months ago add a comment