Definition: A peptide is a short chain of amino acids, the same building blocks that make up proteins. US rules draw the line by length: a chain of more than 40 amino acids is a protein, so 40 or fewer is a peptide. Pramlintide, ipamorelin and GLP-1 medicines such as semaglutide are peptides.
Most peptides are broken down in the gut, so almost all of them are injected. They usually come either as a ready-to-use pen or as a dry powder in a vial that you mix with water before use (see reconstitution). That second form is why peptide logs need more than a dose: you also need the vial size, how much water went in, and the date you mixed it.
Peptide doses are small. Many are written in micrograms (mcg), where 1 mg = 1,000 mcg. A mistake between mcg and mg is a 1,000-fold error, so write the unit every time.
Dose Track saves each vial with its mix date and concentration, so a logged dose in syringe units can be shown in mg or mcg.
Federal rules define a protein as a chain of "greater than 40 amino acids" (21 CFR 600.3). FDA guidance from December 2023 uses "peptide" for any chain of 40 or fewer amino acids and says a peptide that meets the definition of a drug is generally regulated as a drug, which means it needs FDA approval before it can be sold.
Counting amino acids
Read more on Dose Track: Peptide reconstitution calculator · Peptide storage guides