Katie Mullenfounder, marker 82 co (content creator + affiliate marketing)

How to find a legit peptide supplier

11 Jun 2026 · 1 min

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1:00

In this concise instructional video, Katie Mullen shares the key criteria she uses to verify the legitimacy of peptide suppliers. She outlines four main checkpoints: (1) confirming third‑party Certificate of Analysis (COA) testing that verifies peptide purity and composition; (2) ensuring endotoxin testing is performed to detect bacterial contamination, which many suppliers omit; (3) demanding supplier transparency by matching batch numbers on the vial with those listed on the COA and reviewing batch documentation; and (4) evaluating real‑world efficacy after consistent use, such as appetite suppression with GLP‑1 peptides or gradual benefits from GHK‑Cu. She emphasizes that if expected effects do not materialize, it may be a sign to reassess the source.

Chapters

When I first started peptides, the biggest question was, how do you know that what you're getting is legitimate? Here's a few things that I look for now. The first thing is third-party COA testing that shows the purity and confirms what's actually in the vial. Second is what's called endotoxin testing, which checks for things like bacterial contaminants. I found that most online suppliers have COA testing, but a lot of them don't have endotoxin testing. So that's one thing just to keep an eye out for as an extra layer of safety. And then third is transparency from the supplier. I want to see batch testing and documentation and make sure that the batch number on the actual vial matches the batch number of the COA testing that is being published. I think this goes without saying, but the last thing, especially after you've been using them for a while, is whether they're actually working. Especially like GLPs, you can tell if your appetite is suppressed, you can tell that you feel a little bit different. And then things like GHK-CU is more of a long game, but you should start to see some benefits after a while. And if you don't, maybe Maybe it's time to question it.