Buy P21 USA : 17 suppliers prices compared

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

1. The certificate names a laboratory you can find independently, and ideally one with no stake in the result.
2. It carries a batch or lot number that matches the product page or the vial label, and a test date.
3. It confirms identity by mass spectrometry, not only purity by HPLC. Purity alone does not show the vial contains P21.
4. It includes the chromatogram and mass spectrum, not just a summary table.
5. 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 company name, address or way to contact the business 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.