What are peptides?

Proteins and peptides are all built from the same alphabet: amino acids. The main structural differences are:

• Amino acid: a single building block.
• Peptide: a short chain of amino acids (for example, a few to a few dozen).
• Protein or polypeptide: a longer chain that may fold into complex shapes with multiple domains.

There is no single universal cutoff in biochemistry, but regulators have had to draw one. In the United States, the FDA's 2020 final rule defines a protein as "any alpha amino acid polymer with a specific, defined sequence that is greater than 40 amino acids in size" (85 FR 10057). Chains of 40 amino acids or fewer fall outside that definition and are generally regulated as small-molecule-style drugs; longer ones are biologics. The rule works through a concrete example: insulin's two chains contain 21 and 30 amino acids, so at 51 total it counts as a protein — which is why insulin transitioned to biologic regulation in March 2020.

In human biology, peptides can serve many roles, such as:

• Hormones and signalling molecules (for example, GLP-1, oxytocin, or certain appetite-related peptides).
• Fragments of larger proteins that carry out specific tasks.
• Local signalling at tissues involved in healing, inflammation, or metabolism.

Because they are built from amino acids, peptides are often metabolized by the same enzymes that break down proteins. Semaglutide is a clean illustration: its label states that the primary route of elimination is "metabolism following proteolytic cleavage of the peptide backbone," and that it is a GLP-1 analogue with 94% sequence homology to the human hormone (Ozempic prescribing information).

Peptide medicine is not new. Since insulin arrived in the 1920s, more than 80 peptide drugs have reached the market across diabetes, cancer, osteoporosis, multiple sclerosis, HIV infection and chronic pain (Nat Rev Drug Discov 2021); a review maintaining a dataset of peptides that entered human studies counted over 150 in active development (Bioorg Med Chem 2018). In modern medicine and research, peptides appear in several contexts:

• Approved peptide-based drugs, such as certain GLP-1 receptor agonists for diabetes and obesity.
• Experimental therapeutic peptides being tested for roles in healing, immune modulation, or other areas.
• Research-use-only compounds sold to laboratories and, in some markets, wellness-oriented clinics.

The same word, "peptide," can therefore refer to:

• A naturally occurring hormone.
• A highly regulated prescription medicine.
• An early-stage experimental molecule.

Context—how the peptide is made, studied, and used—matters as much as its basic structure.

Examples of peptides discussed in the Standard Peptides catalog include:

• Semaglutide, a GLP-1 receptor agonist used as a medication.
• BPC-157 and TB-500, experimental peptides often discussed in healing and recovery contexts.
• GHK-CU, a copper-binding peptide fragment seen in cosmetic and regenerative discussions.

Each of these has a different evidence base, regulatory status, and safety profile, even though all can be described as "peptides." The gap is wide: semaglutide carries an FDA label with defined indications, dosing, warnings and a boxed warning (Ozempic prescribing information), whereas when the FDA reviewed BPC-157 and the thymosin beta-4 fragment sold as TB-500 for use in pharmacy compounding, it reported "no, or only limited, safety-related information" for the proposed routes of administration, alongside concerns about peptide-related impurities and immunogenicity.

Several trends have pushed peptides into the spotlight:

• Success of incretin-based drugs for metabolic disease.
• Increased interest in regenerative medicine and tissue-specific signalling.
• Growth of wellness and performance markets that highlight experimental compounds.

This mix creates both opportunity and confusion—opportunity because new biology can translate into useful therapies, and confusion because marketing language often blurs the line between early research and established care.

To go deeper:

• Read about different types of peptides.
• Explore the peptides catalog for compound-specific entries.
• Pair basics with the downsides and safety context.