A Plain-English Glossary

Peptide

A short chain of amino acids, the building blocks of proteins. Your body makes thousands of them, and insulin has been a peptide medicine for over a century.

Amino acid

One of the small molecules that link together to form peptides and proteins. Think of them as the letters that spell out a peptide.

Protein

A large chain of amino acids. A peptide is a shorter version of the same kind of molecule.

Compounding

When a licensed pharmacist prepares a medication for a specific patient, for example at a custom dose or without an ingredient the patient reacts to, rather than dispensing a mass-produced product.

503A pharmacy

A compounding pharmacy that prepares medications for individual patients based on a prescription. Regulated by state boards of pharmacy.

503B outsourcing facility

A facility that compounds medications in larger batches and registers with the FDA, which inspects it. Held to stricter manufacturing standards than a 503A pharmacy.

Bulk substance / bulk list

The active ingredients a pharmacy is permitted to use in compounding. Whether a given peptide is eligible to be compounded depends on whether it is on the relevant list, which is part of what the PCAC reviews.

PCAC

The Pharmacy Compounding Advisory Committee, an advisory body to the FDA. It reviews the science and recommends which substances are appropriate for compounding. It advises; it does not write the final rule.

FDA

The U.S. Food and Drug Administration, the federal agency that regulates medicines, including which peptides are approved and which are eligible for compounding.

Gray market

The unregulated channel where peptide therapies are often sold without oversight, including online vendors and products labeled "for research use only." No inspection, no verified quality, no clinical supervision.

Research use only (RUO)

A label some products carry that means they are intended for laboratory research, not for use in people. It is legal positioning, not a safety guarantee, and it does not mean a product has been tested or cleared for human use.

Certificate of analysis (COA)

A document that is supposed to verify a product’s identity and purity. In the gray market, certificates can be missing or faked, which is one reason source matters so much.

FAERS

The FDA Adverse Event Reporting System, a database of reports about possible problems with medications. Reports show events that are associated with a product; they are not by themselves proof that the product caused the event.

Public comment

Input that anyone can submit to the FDA during an open comment period, on regulations.gov. It becomes part of the public record the committee can consider. Comments filed by July 9, 2026 are provided directly to the committee.

Now that the terms make sense, see what the hearing decides: What the Hearing Is and Why It Matters.