What muscle peptides have actually been tested for, and what vendors show.
We read the trials and the vendor paperwork for the compounds people search for, from CJC-1295 to IGF-1 LR3 to follistatin. Every fact carries a date and a source, and every page says what we could not confirm.
Read the muscle researchNo dosing and no protocols. Research materials are sold for laboratory use only. See how the vendors compare on paperwork.
Muscle peptide research
Compound by compound, what each trial measured, in whom, and what the vendor listings claim.
- Peptides for muscle recovery: what is known about BPC-157 and TB-500
- Growth hormone secretagogues explained: GHRH analogs, GHRPs and MK-677
- Peptides vs steroids: how they differ in law, anti-doping rules and evidence
- Follistatin 344: what it is and what has been tested in people
- Sermorelin vs tesamorelin: what separates them and what each has shown
- Myostatin inhibitors explained: what the trials found and what vendors list
Retatrutide-class research starts with tirzepatide.
Core Power Peptides doesn't sell retatrutide, the triple-agonist peptide most researchers ask us about. It sells tirzepatide, the dual GIP/GLP-1 compound its own listing calls a benchmark for that class, at a stated 99%+ purity, shipped from the USA. We checked four vendors on paperwork; this is the one we send readers to buy from, and we say exactly why below.
Shop tirzepatide — $320.00Affiliate link. We earn a commission if you buy through it — see the disclosure.
Featured listing · Core Power Peptides
Tirzepatide 50mg
$320.00 was $416.00
- Free US shipping over $100
- 2–5 day US shipping (stated)
- 100% Made in the USA (stated)
- Widest catalog of the 4 vendors we checked (101 products)
- Class
- Dual GIP/GLP-1 receptor agonist
- Purity
- ≥99% (HPLC verified, per listing)
- Format
- Lyophilized powder
- Storage
- −20°C, protected from light
- CAS number
- 2023788-19-2
- Molecular weight
- 4,813.5 Da
We could not find a published certificate of analysis for this exact listing when we checked — its COA tab shows no report. See what we could and couldn't verify before you buy.
Why we send readers to Core Power Peptides
On our own documentation score, Core Power Peptides is third of four — Peptryn and American Peptides both publish more. We recommend Core Power Peptides anyway, for reasons that are commercial and practical, not about paperwork, and we'd rather say that plainly than blur the two.
Why we picked them
The widest catalog of the four vendors we checked — 101 products, including the GLP-1/GIP family: tirzepatide, semaglutide, cagrilintide and mazdutide.
Competitive, published pricing with an active sale on tirzepatide at the time we checked ($320.00, down from $416.00).
States US manufacturing, free domestic shipping over $100, and 2–5 day US delivery.
Runs a straightforward affiliate program paying 25% commission per referred sale, the the highest base rate of the four we reviewed, which is how this site is funded.
What we're upfront about
Its COA library isn't public. One sample certificate covers one product; the tirzepatide listing we link to shows none.
No full legal entity name or street address appears on the site.
It doesn't sell retatrutide, despite content on its own site aimed at that search term. If retatrutide itself is what you're after, not the tirzepatide we feature, Peptryn and American Peptides both stock it directly, and they rank first and second of the four vendors on documentation.
Full findings are in our Core Power Peptides review.
The paperwork, vendor by vendor
Purity is a number. Here's the trace behind it: four vendors, ranked on what they can actually document, not on who we're paid by.
Checked 29 September 2026 from each vendor's public pages. Claims are the vendors'. We did not test any product.
| Rank | Vendor | Documents on file | Purity on file | Method | Reviewer note |
|---|---|---|---|---|---|
| 1 | Peptryn | Outside lab: PassBatch-matched: PassMethod stated: Pass | 99.6 to 99.97% | HPLC-UV-MS | Complete public paperwork for the products we checked.Read the review |
| 2 | American Peptides | Outside lab: PassBatch-matched: PartialMethod stated: Pass | 99.55 to 99.83% | LC-MS/MS and RP-HPLC (214 nm) | A public COA library with named lab, lots and methods; unclear which lot ships, and we could not check the lab's verification page.Read the review |
| 3 | Core Power Peptides | Outside lab: PartialBatch-matched: PartialMethod stated: Pass | 99% (sample COA) | HPLC and MS (stated) | The catalog and price we recommend; the paperwork still has real gaps.Read the review |
| 4 | Peptides for Sale | Outside lab: FailBatch-matched: FailMethod stated: Partial | Claims 99%+ | HPLC (claimed on product images) | Purity and testing claims with no documents.Read the review |
Purity on file is the figure a vendor publishes or shows on a certificate. Each review says which. Scoring: pass is 2 points, partial is 1, fail is 0, across the three document checks. Read the full comparison, or see the American Peptides product list.
How we check a vendor's paperwork
The ranking above is a checklist, not an opinion. Each criterion is something you can look up yourself in the vendor's own documents.
- An outside lab wrote the report
- A vendor's own bench report shows what the vendor believes. An independent lab report shows what was measured.
- The report names the batch you would receive
- A lab result only counts for the vial in front of you if its batch number matches the label.
- The method is stated
- HPLC shows how much of the sample is the target compound. Mass spectrometry shows whether that compound has the right mass. We record which ones were run.
- The figure is reproducible
- Vendors that publish the raw trace, not just a percentage, let a reader check the number for themselves.
Research guides
Plain-language explainers on peptide chemistry, lab paperwork and the regulatory backdrop — written to be read before you buy anything, not after.
- What a peptide is, in plain language
- How to read a certificate of analysis
- HPLC purity and mass spectrometry: what each one shows
- How to spot a fake or copy-pasted certificate of analysis
- What research-use-only labeling does and does not mean
- Storing lyophilized peptides: the research handling basics
- GLP-1, GIP and glucagon agonists: what “dual” and “triple” mean
Comparisons and certificate guides
Side-by-side comparisons and certificate walkthroughs, each dated and sourced to the vendor pages we read.