A peptide is a short chain of amino acids linked together.  Peptides are similar to proteins, except they contain fewer amino acids and are smaller.   In our bodies, peptides act as signaling molecules that bind to receptors on the cell surface and tell other cells and molecules what to do.

Peptide therapy, or the use of specific peptides in treatment, has gained great popularity in recent years. This is due largely to the fact that these peptides are highly specific (i.e., only do what you want them to do) while also being well-tolerated and safe. As of January 2015, there were over 60 US FDA-approved peptide medications, 140 peptide drugs being evaluated in clinical trials, and 500 in pre-clinical development.