Peptides and GLP-1 Medications: What They Are and Where the FDA Stands

Peptides and GLP-1 Medications: What They Are and Where the FDA Stands

If you have read anything about GLP-1 medications, you have probably seen the word peptide. Semaglutide, tirzepatide, liraglutide, and dulaglutide are all described as peptide-based drugs. This guide explains what peptides are, how the GLP-1 medicines you may be taking fit into that category, and how the U.S. Food and Drug Administration (FDA) reviews and approves them. It also covers compounded products and the "research peptides" sold online — and why those are not the same thing as an FDA-approved medication.

What is a peptide?

A peptide is a short chain of amino acids. Amino acids are the building blocks that your body uses to make proteins. The practical distinction is mostly about size: peptides are generally short chains (often defined as roughly 2 to 50 amino acids), while proteins are longer, folded chains.

Your body makes thousands of peptides naturally. Insulin is one of the most familiar examples. Glucagon-like peptide-1 (GLP-1) is another — it is a hormone released in your gut after you eat. Natural GLP-1 helps regulate blood sugar, slows stomach emptying, and signals fullness to your brain. It is broken down quickly by an enzyme called DPP-4, which is one reason scientists developed longer-lasting versions as medicines.

How GLP-1 medications fit in

GLP-1 receptor agonists are medications designed to mimic or enhance the effects of natural GLP-1. Most of them are peptide-based — meaning the active drug molecule is a peptide, usually a modified version of a natural peptide that lasts longer in the body.

• Semaglutide (Ozempic, Wegovy, Rybelsus) is a modified peptide modeled on human GLP-1.
• Tirzepatide (Mounjaro, Zepbound) is a peptide that acts on both the GLP-1 and GIP receptors.
• Liraglutide (Victoza, Saxenda), dulaglutide (Trulicity), and exenatide (Byetta, Bydureon) are also peptide-based GLP-1 receptor agonists.

Because these molecules are peptides, they typically cannot be taken as an ordinary pill that survives stomach acid — most are injected. (Rybelsus is a special oral formulation of semaglutide that uses an absorption-enhancing technology.)

How the FDA reviews and approves peptide drugs

Peptide drugs go through the same rigorous approval pathway as other new drugs in the United States. A manufacturer must submit a New Drug Application (NDA) (or a Biologics License Application, depending on the product) supported by data from preclinical studies and multiple phases of clinical trials in humans. The FDA reviews the evidence for safety, effectiveness, and manufacturing quality before approval.

The approval process generally includes:

• Preclinical laboratory and animal studies to assess basic safety.
• Phase 1 trials to test safety in a small group of people.
• Phase 2 trials to evaluate effectiveness and side effects.
• Phase 3 trials in larger groups to confirm effectiveness and monitor for less common side effects.
• FDA review of all the data, the proposed labeling, and the manufacturing facilities.

This is why an FDA-approved peptide medication has a known identity, purity, dosage, and labeling — and why the manufacturer is required to report adverse events.

Branded, generic, and "biologics-like" peptide products

Most GLP-1 receptor agonists are still under patent and available only as branded products. A generic drug is an exact copy of an approved small-molecule drug, made after the patent and exclusivity periods end. Peptide drugs can be complex to copy, and some are regulated as biologics, which means "copies" may follow a biosimilar pathway rather than a traditional generic pathway. The practical point: a true FDA-approved equivalent has been reviewed by the FDA for sameness and safety. Anything that has not been through that process is not an FDA-approved drug.

Compounded peptides: the 503A and 503B framework

Compounding is the practice of a pharmacist preparing a customized medication. Under U.S. law:

• Section 503A covers traditional compounding by a licensed pharmacist or physician in response to a patient-specific prescription.
• Section 503B covers outsourcing facilities that compound drugs in larger quantities, subject to current good manufacturing practice (cGMP) requirements.

Compounded drugs are not FDA-approved. The FDA does not review them for safety, effectiveness, or quality before they are dispensed. Compounding is allowed in certain circumstances — historically including during a national shortage of an approved drug — but a compounded product does not carry the same assurances of identity, potency, purity, and sterility as an FDA-approved product.

When an approved GLP-1 medication is in shortage, some compounding of that active ingredient has occurred. When the shortage ends, the FDA's position is that compounding of essentially a copy of the approved drug should generally stop. The FDA has removed semaglutide and tirzepatide from its shortage list as supply improved, which has significant implications for compounded versions of those medications.

"Research peptides": what they are and why they are not a substitute

Online sellers sometimes market semaglutide, tirzepatide, or other peptides with labels like "for research purposes only," "not for human consumption," or "not for diagnostic or therapeutic use." These are sometimes called "research peptides."

These products are not FDA-approved drugs. They are not manufactured to drug-grade standards, they are not reviewed for safety or effectiveness, and selling them for human use is outside the framework intended by those disclaimers. They are not a substitute for a prescription medication from a licensed pharmacy.

GLP-1 Primer does not include research-peptide sellers in its research index. Our inclusion criteria specifically exclude entities selling semaglutide or tirzepatide labeled for research or non-human use.

What to look for if you are evaluating a GLP-1 medication

• Is the product an FDA-approved branded medication dispensed by a licensed pharmacy?
• If it is compounded, is it being provided through a properly licensed 503A pharmacy or 503B outsourcing facility, with a valid prescription from your clinician?
• Is the prescribing and dispensing entity clearly identified?
• Are storage and handling requirements clearly explained (many peptide injectables require refrigeration)?

The bottom line

GLP-1 receptor agonists are peptide-based medications that have gone through formal FDA review. That review is what gives you confidence in a product's identity, dose, purity, and labeling. Compounded products are not FDA-approved and carry different — and greater — uncertainty. Products sold as "research peptides" are not medications and are not a substitute for a prescription from your clinician.

This article is educational and is not medical advice. Talk with your licensed healthcare provider about any medication decisions, and report suspected adverse events to your clinician and to the FDA's MedWatch program.