Peptides 101: What You Should Know First
Peptides are getting a lot of attention online. This guide explains what they are in plain words. It also shows why the type of product matters so much and what to check before you go any further.
What is a peptide?
Amino acids are small building blocks. Your body uses them to make proteins. A peptide is a short chain of amino acids linked together. Most peptides have about 2 to 50 amino acids. A longer chain is called a polypeptide, and proteins are made from one or more of these.
The FDA draws its own line. For its rules, a chain of more than 40 amino acids counts as a protein. That means a peptide has 40 or fewer.
Some peptides are real medicines. The FDA has approved peptide drugs such as glucagon, teriparatide and calcitonin salmon. But many products called "peptides" online are not approved medicines at all.
Three kinds of peptide products
Products can look alike but be very different. Here are the three main kinds.
1. FDA-approved drugs
- The drug company tested the drug in people and sent its data to the FDA.
- FDA experts reviewed the data. They decided the drug's benefits outweigh its known risks for the people it's meant for.
- Many approved drugs are prescription drugs. A doctor prescribes them for one person, and you get them at a pharmacy.
- You can look up approved drugs in the FDA's free Drugs@FDA database.
2. Compounded drugs
A compounded drug is mixed or made by a pharmacy or a special facility. It isn't made by a drug company. Federal law has two main paths:
- 503A pharmacies are state-licensed pharmacies. They make a drug for one named patient, based on a valid prescription. State pharmacy boards do most of the oversight.
- 503B outsourcing facilities register with the FDA. The FDA inspects them, and they must follow stricter manufacturing quality rules. They may make drugs with or without a prescription for a specific patient.
Compounded drugs are not FDA-approved. The FDA doesn't check their safety, effectiveness or quality before they're sold. The FDA says compounded drugs should only be used when a patient's needs can't be met by an FDA-approved drug.
3. "Research use only" products
Some products online say "research use only" or "not for human consumption." Those labels mean the product is not meant for people.
The FDA has warned companies that sold some of these products to people, with dosing instructions. The FDA said those products were falsely labeled. It urges consumers not to buy these products. Their quality is unknown and they may be harmful to your health.
Why this matters
| FDA-approved | Compounded | "Research use only" | |
|---|---|---|---|
| FDA reviewed safety and effectiveness? | Yes | No | No |
| Made under FDA manufacturing quality rules? | Yes | 503B: yes. 503A: no, state rules apply | Unknown |
| Meant for people? | Yes, as labeled | Yes, for patients who need them | No, by its own label |
Risks and unknowns
- Wrong or harmful contents. The FDA warns that drugs sold illegally online may be fake (counterfeit). They may hold the wrong ingredient, or too much, too little or none of the right one.
- Contamination. The FDA says poor compounding can cause contamination or the wrong amount of drug. This can lead to serious injury and even death.
- Not enough safety data. The FDA keeps a list of substances that "may present significant safety risks" when used in compounding. For many of the peptides on it, the FDA says it "lacks sufficient information to know whether the drug would cause harm" in people. The peptides are listed below, under the FDA's own headings.
- Immune reactions. For many peptides on that list, the FDA notes a risk of "immunogenicity." That means the body's immune system could react to the product or its impurities.
- Problems may go unreported. State-licensed pharmacies that aren't FDA-registered outsourcing (503B) facilities don't have to report side effects to the FDA. So the true number of problems may be higher than what's known.
Peptides on the FDA's safety-risk list
This is a list of safety warnings, not a list of products to try. The FDA placed these substances on this list because they "may present significant safety risks" when used in compounding.
These names are copied exactly as the FDA writes them on its page "Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks." The page is about "Category 2 of the Bulk Substances Nominated Under Sections 503A or 503B of the Federal Food, Drug, and Cosmetic Act." We list only the entries where the FDA's own text mentions peptides. The FDA's list also includes other substances. See the FDA page for all of them and its full wording on each one. Checked 2026-10-19.
"Bulk drug substances under category 2 of the interim policies"
| FDA name | FDA category |
|---|---|
| Growth hormone releasing peptide-2 (GHRP-2) (for injectable and nasal routes of administration) | 503B |
| Growth hormone releasing peptide-6 (GHRP-6) | 503B |
| Ipamorelin acetate | 503B |
| Kisspeptin-10 | 503A |
"Bulk drug substances nominated but withdrawn" (the FDA says these were "previously in category 2 of the interim policies" and "were withdrawn by the nominators")
"Withdrawn" means the people who asked for these to be allowed in compounding withdrew their requests. It does not mean the FDA found them safe.
- AOD-9604
- BPC-157
- Cathelicidin LL-37
- CJC-1295
- Emideltide (DSIP)
- Epitalon
- GHK-Cu (for injectable routes of administration)
- Ipamorelin acetate (the FDA notes it "also appears in the table above because it is in category 2 under the 503B interim policy")
- Mechano growth factor pegylated (PEG-MGF)
- Melanotan II
- MOTs-C
- Selank acetate (TP-7)
- Semax (heptapeptide)
- Thymosin-alpha 1 (Ta1)
- Thymosin beta-4, fragment (LKKTETQ), also known as TB-500
The FDA's list can change. Check the FDA page for the latest version.
If you have a bad reaction to any medicine or product, you can report it to the FDA's MedWatch program.
How to check testing
Some sellers share a lab report, called a certificate of analysis (COA). A COA can be useful, but only if it's real and matches your product. Our guide on how to check a COA walks you through it step by step. You can also find third-party testing labs.
Keep in mind that a lab test describes one sample on one day. A good test result does not mean a product is safe or right for you.
Talk to a doctor
The FDA recommends talking with your healthcare provider before taking any medicine. A doctor or pharmacist can:
- tell you whether an FDA-approved option exists
- talk with you about your other medicines and health conditions
- help you read labels and lab reports
Bring a list of everything you take, including vitamins and supplements. Use our questions to ask your doctor to get ready. If a word confuses you, check our glossary.
Keep reading
Sources
All official sources, checked 2026-10-19.
- MedlinePlus (NIH), "Amino acids": https://medlineplus.gov/ency/article/002222.htm
- NHGRI (NIH), Talking Glossary, "Peptide" (short chain, typically 2 to 50 amino acids; polypeptides; proteins): https://www.genome.gov/genetics-glossary/Peptide
- 21 CFR 600.3(h)(6), definition of "protein" (more than 40 amino acids): https://www.ecfr.gov/current/title-21/chapter-I/subchapter-F/part-600/subpart-A/section-600.3 (the text was confirmed through the Cornell LII copy, https://www.law.cornell.edu/cfr/text/21/600.3, because eCFR blocks automated fetches)
- FDA, "FDA Publishes Revised Draft Product-Specific Guidances for Certain Generic Peptide Products" (7/28/2026): lists approved peptide products, including glucagon, teriparatide and calcitonin salmon: https://www.fda.gov/drugs/drug-alerts-and-statements/fda-publishes-revised-draft-product-specific-guidances-certain-generic-peptide-products
- FDA, "Development & Approval Process | Drugs" (what FDA approval means): https://www.fda.gov/drugs/development-approval-process-drugs
- FDA, "Prescription Drugs and Over-the-Counter (OTC) Drugs: Questions and Answers": https://www.fda.gov/drugs/frequently-asked-questions-popular-topics/prescription-drugs-and-over-counter-otc-drugs-questions-and-answers
- FDA, Drugs@FDA: https://www.accessdata.fda.gov/scripts/cder/daf/
- FDA, "Compounding and the FDA: Questions and Answers" (not FDA-approved; who compounds; oversight; CGMP for outsourcing facilities; risks such as contamination and too much or too little active ingredient): https://www.fda.gov/drugs/human-drug-compounding/compounding-and-fda-questions-and-answers
- FDA, "FD&C Act Provisions that Apply to Human Drug Compounding" (503A vs 503B; patient-specific prescriptions; registration; adverse event reporting): https://www.fda.gov/drugs/human-drug-compounding/fdc-act-provisions-apply-human-drug-compounding
- FDA, "FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss" (products falsely labeled "for research purposes" or "not for human consumption"; fake and wrong-dose products; underreporting; talk to your doctor; MedWatch): https://www.fda.gov/drugs/drug-alerts-and-statements/fdas-concerns-unapproved-glp-1-drugs-used-weight-loss
- FDA, "Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks" (the list of peptide names, category headings and 503A/503B designations was copied exactly and rechecked 2026-10-19; "lacks sufficient information to know whether the drug would cause harm"; immunogenicity risk. Peptides were chosen as the entries whose FDA text mentions "peptide" or "peptide-related impurities". KPV and Dihexa acetate are on the same withdrawn list, but FDA's text doesn't call them peptides, so they were left out pending a decision): https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
- FDA, MedWatch: https://www.fda.gov/safety/medwatch-fda-safety-information-and-adverse-event-reporting-program
- FDA, "Preliminary Recommendations for State Recognition of Outsourcing Facilities" (states regulate 503A pharmacies, including quality requirements): https://www.fda.gov/media/100224/download
- MedlinePlus (NIH), "Talking With Your Doctor" (bring a list of medicines and supplements): https://medlineplus.gov/talkingwithyourdoctor.html