What Are Peptides? A Clear Guide to How They Work in the Body

What are peptides?

Peptides are short chains of amino acids, typically 2 to 50, linked by peptide bonds. Your body makes many of them, including oxytocin (9 amino acids), the gut hormone GLP-1 (30), and glutathione (3). Longer chains fold into proteins. Online, the single word “peptides” covers FDA-approved prescription drugs, compounded prescriptions, cosmetic ingredients, supplements, and unapproved research chemicals, and each of those carries a different legal status.

Peptides vs proteins: where scientists and the FDA draw the line

That 2 to 50 range comes from the National Human Genome Research Institute. A chain of 51 or more is a polypeptide, and proteins are built from one or more polypeptides folded into working shapes.

The FDA draws its legal line elsewhere. In the rulemaking that defined “biological product,” the agency interpreted “protein” to mean any alpha amino acid polymer with a specific, defined sequence greater than 40 amino acids in size. Products above that threshold, insulin among them, moved to biological-product regulation on March 23, 2020. A molecule can therefore be a peptide in a biology textbook and a protein in the FDA’s rulebook at once.

Peptides your body already makes

Your own body makes peptides constantly: oxytocin, glutathione, and the gut hormone GLP-1 are all peptides, and all three sit well inside the 2 to 50 range. Insulin, at 51 amino acids, sits just past that line, which is why it is usually called a polypeptide and is regulated as a biological product, even though it is still described as the first therapeutic peptide drug. It comes from the beta cells of the pancreas and was isolated in 1921.

GLP-1: the gut hormone behind the GLP-1 drugs

Glucagon-like peptide-1 is a gut hormone released after you eat. When it reaches its receptors it prompts insulin secretion, suppresses glucagon, increases satiety, and delays stomach emptying. The natural hormone is also broken down almost as fast as it appears, the problem drug designers had to solve.

How peptides work in the body

Most peptides act as messengers: one travels through the bloodstream, binds a receptor on a target cell, and that receptor relays the signal inside. The receptor makes the message specific: semaglutide binds the GLP-1 receptor, while bremelanotide (PT-141) is a melanocortin receptor agonist.

Two properties make peptides awkward as medicines. A 2022 review in Signal Transduction and Targeted Therapy, which counts more than 80 peptide drugs approved worldwide since insulin was isolated in 1921, names two intrinsic drawbacks: membrane impermeability and poor stability in the body. Swallowing a peptide puts it in the path of digestive enzymes that break its amide bonds apart, and what survives crosses the gut wall poorly, so little of an oral dose reaches the bloodstream, which is why injection under the skin is the usual route. Oral dosing is possible with formulation work: the current Wegovy label covers semaglutide tablets as well as injection.

Designers work around those limits by editing the sequence and attaching fatty acids: the same review describes liraglutide, an earlier GLP-1 analogue, as carrying an attached C-16 fatty acid (palmitic acid). The clinical pharmacology section of the Wegovy label describes semaglutide as a GLP-1 analogue with 94 percent sequence homology to human GLP-1, and sequence changes plus a fatty-acid modification slow its breakdown enough for weekly injection (the tablets are taken once daily). Tirzepatide, a dual GIP and GLP-1 receptor agonist, is injected once weekly.

The five things people mean when they say “peptides”

One word covers at least five kinds of product with different legal footing. The compounding and approval rows reflect FDA materials current as of September 2026, and none of this is legal advice.

Category	Regulatory status (U.S.)	Examples
FDA-approved peptide drugs	FDA-approved, with labeled indications, populations, warnings, and dosing	Wegovy, Ozempic (semaglutide); Mounjaro, Zepbound (tirzepatide); Vyleesi (bremelanotide)
Compounded prescription peptides, made for one patient by a 503A pharmacy	Not FDA-approved, and not evaluated by the FDA for safety, quality, or efficacy; permitted only where the substance meets a section 503A criterion or sits in Category 1 of the FDA’s interim policy	Glutathione (503A Category 1); PT-141 (bremelanotide is a component of approved Vyleesi); sermorelin, whose only basis is a discontinued approved product, not confirmed by the FDA (see below); compounded semaglutide or tirzepatide only on documented individual need
Research peptides with no approved product, sold online as “research use only”	Not FDA-approved; none meets a 503A criterion or sits on the Bulks List, and some are in Category 2, the FDA’s significant-safety-risk category, so none can be lawfully compounded for people	BPC-157, TB-500, CJC-1295, MOTS-c, AOD-9604, KPV, epitalon, Semax, kisspeptin-10
Cosmetic peptides in creams and serums	Sold as cosmetics, not as prescription medicines, and not FDA-approved drugs	Peptide serums, copper peptide (GHK-Cu) creams
Supplement peptides in powders and capsules	Sold as dietary supplements, not as prescription medicines; the FDA does not approve dietary supplements before they are marketed, so they are not FDA-approved drugs	Collagen peptide powders

FDA-approved peptide drugs: what approval actually means

An FDA-approved drug has completed review for a specific use in a specific population, and its label sets out indications, dosing, and risks.

• Semaglutide (Wegovy). A GLP-1 analogue with 94 percent sequence homology to human GLP-1; initial U.S. approval 2017. The uses below are Wegovy’s; Ozempic is a separate semaglutide product with its own label. Wegovy comes as an injection and as tablets, both indicated alongside a reduced calorie diet and increased physical activity, and the two forms do not carry the same uses. The injection has three uses: lowering the risk of major adverse cardiovascular events in adults with established cardiovascular disease and either obesity or overweight; reducing excess body weight and maintaining that reduction long term in adults and in pediatric patients aged 12 years and older with obesity, or in adults with overweight plus at least one weight-related comorbid condition; and, under accelerated approval, noncirrhotic metabolic dysfunction-associated steatohepatitis (MASH) with moderate to advanced liver fibrosis (stages F2 to F3) in adults. The tablets carry only the first two, in adults only: not for patients under 18, and not for MASH. Both forms carry a boxed warning for risk of thyroid C-cell tumors.
• Tirzepatide (Mounjaro, Zepbound). A dual GIP and GLP-1 receptor agonist; initial U.S. approval 2022. The two brands have separate labels. The Mounjaro label includes two uses: improving glycemic control, with diet and exercise, in adults and pediatric patients 10 and older with type 2 diabetes, and reducing the risk of major adverse cardiovascular events in adults with type 2 diabetes at high risk for those events. The Zepbound label carries two different uses, both in combination with a reduced calorie diet and increased physical activity: reducing excess body weight and maintaining that weight reduction long term in adults with obesity, or in adults with overweight plus at least one weight-related comorbid condition; and treating moderate to severe obstructive sleep apnea (OSA) in adults with obesity. An FDA-approved tirzepatide for weight management therefore does exist. Same boxed warning. See tirzepatide vs semaglutide.
• Bremelanotide (Vyleesi). A melanocortin receptor agonist approved in June 2019 for one population only: premenopausal women with acquired, generalized hypoactive sexual desire disorder. It is not approved for men, and any compounded PT-141 is off-label and not FDA-approved. See what PT-141 is.

Approval attaches to the product and the use, not the molecule: the same peptide prescribed off-label or compounded does not inherit it.

Compounded peptides and the 503A rules

Compounding is a pharmacist preparing a medication for one patient on a prescription. Under section 503A of the Federal Food, Drug, and Cosmetic Act, a pharmacy may use a bulk drug substance only if it appears in a USP or National Formulary monograph, is a component of an FDA-approved drug, or sits on the 503A Bulks List the FDA is still building. Until that list is finished, an interim policy sorts nominations: Category 1 may be used pending evaluation if the FDA’s conditions are met, Category 2 raises significant safety risks, and Category 3 lacked adequate support. On the list updated May 14, 2026, Category 1 includes glutathione, NAD, and enclomiphene citrate. Category 2 holds six substances, the only peptide among them kisspeptin-10, alongside non-peptides such as ibutamoren mesylate (MK-677); both sell widely online, so popularity says nothing about status.

Those rules decide what a lawful clinic can offer. Compounding pharmacies have treated sermorelin as eligible because it was once a component of an approved drug that has since been discontinued. The FDA has not said sermorelin qualifies, it appears nowhere on the May 14, 2026 categories list, no approved sermorelin product is marketed today, and compounded sermorelin is not FDA-approved or evaluated by the FDA for safety, quality, or efficacy. Compounded PT-141 is likewise off-label and not FDA-approved, even though bremelanotide is a component of Vyleesi. See how to get sermorelin legally.

Compounded GLP-1s after the shortages

The FDA allowed compounders to copy semaglutide and tirzepatide while the approved drugs were in shortage. That window is closed. The agency announced the tirzepatide shortage resolved on December 19, 2024 and the semaglutide shortage on February 21, 2025, with enforcement discretion for 503A pharmacies running only until February 18 and April 22, 2025. With both drugs available again, the bar on compounding what is essentially a copy of an approved drug applies. A compounded GLP-1 is not FDA-approved and is appropriate only where a prescriber documents that the approved product cannot meet an individual patient’s needs. See compounded tirzepatide in 2026.

BPC-157, TB-500 and the 2026 FDA review: where things stand

The peptides people ask about most online have no FDA-approved product and are not on the 503A Bulks List. The FDA’s safety-risk page, content current April 22, 2026, lists ipamorelin acetate, GHRP-2, and GHRP-6 in Category 2 under the 503B policy, citing immunogenicity risk and thin human safety data.

That same page groups BPC-157, TB-500 (a thymosin beta-4 fragment), CJC-1295, MOTS-c, AOD-9604, KPV, epitalon, and Semax as substances previously in Category 2 whose nominations were later withdrawn, not as listed substances. Withdrawal did not move them into Category 1 or onto the Bulks List. The FDA still publishes the safety risks it identified: risk of immunogenicity for certain routes of administration, plus complexities around peptide-related impurities, for BPC-157 and TB-500; no identified human exposure data by any route of administration for MOTS-c and KPV; and for CJC-1295, serious adverse events including increased heart rate and a systemic vasodilatory reaction, with available clinical data described as limited.

The FDA then referred seven of them, BPC-157, KPV, TB-500, MOTS-c, emideltide (DSIP), epitalon, and Semax, to its Pharmacy Compounding Advisory Committee for the meeting held July 23 and 24, 2026, and its briefing document proposed keeping every form of all seven off the list. A committee recommendation is advisory, and any change to the 503A list must go through rulemaking; the FDA says in that document that it does not intend to issue a final determination until the committee’s input has been considered.

So these substances meet no 503A criterion, no pharmacy can lawfully compound them for human use today, and Revive does not offer them. A “research use only” label does not change that: what governs is whether a substance may lawfully be compounded for people, and these may not. Our FDA July 2026 peptide review follows the process.

How to tell a legitimate peptide program from a risky one

Start by asking which of the five categories a product falls into, then check two things.

• A licensed prescriber evaluates you first, holding a license in your state, and the pharmacy is named: a state-licensed 503A pharmacy or an FDA-registered 503B outsourcing facility.
• No “research use only” vials, no promised outcomes, and no claim of FDA approval for a compounded preparation. Verify licenses and registrations yourself with the state board, the certifying body, or the FDA’s lists.

See also how to choose a licensed online peptide clinic and peptide therapy by telehealth.

How Revive approaches peptide therapy

Revive Longevity is a LegitScript-certified telehealth clinic. Every treatment starts with an evaluation by a licensed U.S. provider, available in all 50 states, who reviews your history and decides whether a prescription is clinically appropriate. Medications are dispensed only on a valid prescription and, where compounded, come from licensed 503A pharmacies. Compounded medications are not FDA-approved, and the FDA has not evaluated them for safety, quality, or efficacy. Our content is reviewed by Diana Medina, PA-C, a board-certified Physician Associate.

The peptides Revive may prescribe include sermorelin ($179 per 4 weeks), PT-141 ($199 per 4 weeks), glutathione ($179 per 4 weeks), and compounded tirzepatide ($279 per 4 weeks). All four are compounded preparations: they are not FDA-approved, and the FDA has not evaluated them for safety, quality, or efficacy. The tirzepatide is considered only where a provider documents an individual clinical need the approved product cannot meet. Pricing is subject to change and eligibility.

Several other Revive therapies are not peptides. NAD+ is a coenzyme, and compounded NAD+ injections and nasal spray are not FDA-approved. Enclomiphene, a small molecule, is not FDA-approved, and enclomiphene citrate sits in Category 1. Testosterone has FDA-approved products; testosterone is a Schedule III controlled substance, and approved products are not approved for age-related low testosterone alone. Approved hCG products exist, and they are not indicated for weight loss. Revive does not offer BPC-157, TB-500, CJC-1295, or ipamorelin.

Frequently asked questions

Are peptides the same as proteins?

No. Both are chains of amino acids, but peptides are short (typically 2 to 50) and proteins are longer chains folded into complex shapes. The FDA’s legal line is more than 40 amino acids, so insulin, at 51, is regulated as a biological product.

Are peptides FDA-approved?

Some are. Semaglutide (Wegovy, Ozempic), tirzepatide (Mounjaro, Zepbound), and bremelanotide (Vyleesi) are FDA-approved, each for specific labeled uses and populations. Compounded peptides, including compounded versions of those same molecules, are not FDA-approved, and the FDA has not evaluated them for safety, quality, or efficacy.

Do I need a prescription for peptides?

For any peptide used as a medicine, yes. FDA-approved and compounded peptides are prescription-only, so a licensed provider evaluates you and decides whether treatment is appropriate. Peptides in cosmetic creams or collagen supplements are not prescription medicines and fall under different rules.

Is BPC-157 legal to prescribe or compound now?

No. BPC-157 has no FDA-approved product and is not on the FDA’s 503A Bulks List. It was previously in Category 2, and the later withdrawal of that nomination did not move it into Category 1. The FDA referred it to its Pharmacy Compounding Advisory Committee for the July 2026 meeting and proposed that it not be listed, so no pharmacy can lawfully compound it for human use.

Are collagen peptides the same as peptide therapy?

No. Collagen peptide powders are sold as dietary supplements, not prescription medicines, and the FDA does not approve dietary supplements before they are marketed, so they are not FDA-approved drugs. Peptide therapy means prescription medications, approved or compounded, prescribed after an evaluation by a licensed provider.

Can compounded semaglutide or tirzepatide still be prescribed?

Only where an individual patient’s needs cannot be met by the FDA-approved product. The FDA announced the tirzepatide shortage resolved on December 19, 2024 and the semaglutide shortage on February 21, 2025, ending the period when compounders could make copies. Compounded GLP-1s are not FDA-approved and require a prescriber’s individualized decision.