At a glance · 10 Nov 2026
- Suppliers serving the US
- 32 list P21; 29 with a listing on sale (36 listings confirmed in stock)
- Based in the US or shipping in
- 27 of the 29 stores with P21 on sale are based in the US; 2 ship in from abroad or do not say where they are based.
- Sizes on sale
- Suppliers on this page sell P21 in 5 mg and 10 mg vials. Some also sell packs of 10 vials, compared per mg of the whole pack rather than against single vials. Other forms on sale (liquid and spray) are different products and are not compared per mg with vials. How prices are compared
- Price per mg, single vials (USD)
- US$3.90/mg to US$24.00/mg, median US$14.00/mg, across 23 single-vial listings from 19 suppliers
- Price per mg, multi-vial packs (USD)
- US$5.00/mg to US$22.20/mg, median US$8.35/mg, across 5 pack listings from 5 suppliers
- Test certificates
- 1 of 32 suppliers have one for P21 on file with us
- Legal status in the US
- The FDA treats research peptides sold for human use as unapproved new drugs and has said in 2026 warning letters that research-use-only labels do not change that. Full summary with sources
What P21 is
P21 (Peptide 021, P021) is a small synthetic peptide derived from a four-amino-acid active region of ciliary neurotrophic factor (CNTF), with an adamantane-modified glycine added to help it resist breakdown and enter the brain. Developed at the New York State Institute for Basic Research, it increased the birth of new neurons, raised BDNF and improved memory in mouse and rat models of ageing, Alzheimer’s disease and Down syndrome. All of that evidence is from animals and cells; no human study of P21 has been published. Read the full P21 guide, with the published research and references.
Before you choose a P21 supplier
Price per mg is only half the comparison. Check that the supplier publishes a certificate of analysis for the batch it is selling, ideally from an independent laboratory, and that the certificate confirms identity as well as purity: our guide on how to read a COA shows what to look for. A price far below the rest of the list is more often a warning than a bargain; peptide prices explained sets out why.
For what P21 is and what published studies have found, see our P21 guide. Handling questions are covered in how to store peptides, and the peptide calculator converts a vial size and water volume into concentration and syringe units. Rules on buying and importing differ by country: read are peptides legal in the US? and see all suppliers serving the US.
Checking a P21 certificate of analysis
- The certificate names a laboratory you can find independently, and ideally one with no stake in the result.
- It carries a batch or lot number that matches the product page or the vial label, and a test date.
- It confirms identity by mass spectrometry, not only purity by HPLC. Purity alone does not show the vial contains P21.
- It includes the chromatogram and mass spectrum, not just a summary table.
- Where the laboratory offers online verification of its reports, the report number checks out.
Red flags
- No certificates at all, or certificates available only “on request”.
- The same certificate used for several products or several years of stock.
- Payment only by cryptocurrency or bank transfer, with a discount for paying that way.
- A price far below every other supplier on this page.
- No way to contact the store other than a web form.
- Vials labelled only with a code rather than the product name and strength.
How to spot a fake peptide supplier explains each of these in more detail, and third-party peptide testing covers what independent results can and cannot prove.
Vials, capsules and pre-mixed products
Most research peptides are sold as freeze-dried (lyophilised) powder in sealed vials, which is mixed with a diluent such as bacteriostatic water before use in the lab. Some suppliers also sell pre-mixed solutions, nasal sprays or capsules under the same name. These are different products with different stability and dosing, so compare price per mg only between the same form, and check which form a listing is before comparing it with the rest of the table.
How this list is built: suppliers appear because they list P21 on their own website, read by our catalogue checks; nobody pays to be included or to move up. Ranking is by PepFinder Score, with stores that have nothing on sale after those that do. Prices, sizes and stock are as each site listed them when checked and may have changed.
