Introduction to Peptide Therapy

Peptides are short chains of amino acids linked together by peptide bonds, the same fundamental building blocks that form proteins. The distinction between a peptide and a protein is largely one of size: by convention, chains of fewer than 50 amino acids are called peptides, while longer chains are proteins, though this boundary is somewhat arbitrary. In biological systems, peptides serve as hormones, neurotransmitters, growth factors, antimicrobial agents, and signaling molecules of remarkable specificity.

What makes peptides therapeutically exciting is their inherent target selectivity. Because they evolved alongside the very receptors they bind, peptides often interact with exceptional precision, a property that synthetic small-molecule drugs struggle to replicate. The human body already synthesizes a wide range of endogenous peptides; therapeutic peptides either mimic, enhance, or modulate these natural signaling cascades (PMID 28720325).

From a practical standpoint, peptides occupy a unique middle ground in pharmacology: they are larger and more selective than small molecules, yet smaller and easier to synthesize than full biologics like monoclonal antibodies. This makes them attractive for indications where receptor specificity is paramount and where the cost and complexity of large biologics would be prohibitive.

Clinical Pearl: When patients ask "aren't peptides just proteins?", explain that all proteins are peptides, but not all peptides are proteins. Insulin, for example, is a 51-amino-acid peptide hormone that many wouldn't intuitively classify as a "peptide drug," yet it was the first commercially available peptide therapeutic and remains one of the most widely used medicines in history.