Weight Loss · Reference
What Is a GLP-1? Meaning, How GLP-1 Medications Work, and the List by Generic Name
This page explains what the hormone is, how GLP-1 medications work, the GLP-1 medications by generic name, how compounded and approved versions differ, where the FDA stands as of September 2026, and what Pepti offers.
Medically reviewed by Dr. Gene, MD · November 4, 2026
Treatments mentioned
GLP-1 stands for glucagon-like peptide-1, a hormone your small intestine releases after a meal that tells the pancreas to release insulin when blood glucose is high, slows how fast the stomach empties, and signals fullness to the brain. The natural hormone is broken down within minutes, so GLP-1 medications are modified versions engineered to last for days, which is what allows a once-weekly injection. Semaglutide acts on the GLP-1 receptor alone; tirzepatide acts on the GLP-1 receptor and on the receptor for GIP, the other gut hormone of the same family. Pepti prescribes compounded semaglutide and compounded tirzepatide, which contain the same active ingredients as the approved products but are not FDA approved.
This page explains what the hormone is, how GLP-1 medications work, the GLP-1 medications by generic name, how compounded and approved versions differ, where the FDA stands as of September 2026, and what Pepti offers.
What Is a GLP-1? Meaning, How GLP-1 Medications Work, and the List by Generic Name
The short answer
| Question | Answer |
|---|---|
| What does GLP-1 stand for? | Glucagon-like peptide-1 |
| What is it? | A gut hormone released after eating, one of the two incretin hormones |
| What does a GLP-1 medication do? | Activates the GLP-1 receptor for days rather than minutes: glucose-dependent insulin release, less glucagon, slower stomach emptying, and quieter appetite signalling |
| GLP-1 medications Pepti prescribes | Semaglutide, from $99/mo, and tirzepatide, from $159/mo |
| Is compounded GLP-1 FDA approved? | No. The active ingredients are approved; compounded preparations are not |
| How is it taken? | A subcutaneous injection once weekly, from a dose-specific vial |
| Do I need a prescription? | Yes, from a physician licensed in your state |
Both prices are "from" prices, because GLP-1 vials are dose-specific and the price moves with the strength. Every price is all-in, covering medication, physician review, refill management and shipping, with no separate membership fee.
What Is a GLP-1? Meaning, How GLP-1 Medications Work, and the List by Generic Name
What is GLP-1?
The hormone
GLP-1 is a peptide hormone released by the small intestine when food arrives. It is one of two incretins, the hormones that explain why a meal produces a larger insulin response than the same amount of glucose given intravenously. The other incretin is GIP, glucose-dependent insulinotropic polypeptide.
The natural hormone works locally and briefly. An enzyme called DPP-4 breaks it down within minutes, which is why GLP-1 itself was never a practical medicine. Every GLP-1 medication is a solution to that problem: a molecule close enough to GLP-1 to activate its receptor, changed so that DPP-4 cannot clear it quickly.
GLP-1 meaning, in one line
When people say "a GLP-1" they almost always mean a GLP-1 receptor agonist: a medication that activates the same receptor the hormone does. "GLP-1" has become shorthand for the whole class, the way people say "a statin."
What does GLP-1 stand for?
Glucagon-like peptide-1. "Peptide" because it is a short chain of amino acids. People search it as "GLP 1," "GLP1" and "GLP-1"; all three mean the same hormone and, in everyday use, the medications that mimic it.
What Is a GLP-1? Meaning, How GLP-1 Medications Work, and the List by Generic Name
How does GLP-1 work?
Unlike most peptides on this site, the GLP-1 mechanisms are established in humans, not only in animals and cells. Four actions are consistently described.
| Action | Where it happens | What it means in practice |
|---|---|---|
| Glucose-dependent insulin release | Beta cells in the pancreas | Insulin is released only when blood glucose is elevated, so a GLP-1 medication on its own rarely drives glucose too low |
| Less glucagon | Alpha cells in the pancreas | The liver is told to release less stored glucose |
| Slower gastric emptying | The stomach | Fullness lasts longer after a meal; also the source of nausea and why anaesthesia teams ask about GLP-1 use |
| Appetite signalling | Hypothalamus and brainstem | Less hunger and fewer cravings, often described by patients as "food noise" going quiet |
Why the effect on appetite matters most
In the weight-management trials, the appetite pathway carries most of the effect. A GLP-1 medication is not a stimulant and does not force the body to burn anything. It works through receptors the body already uses to register that a meal has been eaten, and the change in body weight reported in trials follows from people eating less over a long period.
How the medications last a week
Semaglutide keeps most of the natural GLP-1 sequence and changes three things: an unnatural amino acid at position 8 that blocks DPP-4, a substitution at position 34, and a fatty-acid chain at position 26 that binds the molecule to albumin in the blood. Those changes stretch its half-life to roughly a week. Tirzepatide uses a similar albumin-binding chain and has a half-life of about five days. That is the whole reason both are injected once weekly.
What GIP adds: the dual agonist
Tirzepatide is a 39-amino-acid peptide built on the backbone of GIP and engineered to activate both the GIP receptor and the GLP-1 receptor, which is why the literature calls it a dual GIP/GLP-1 receptor agonist. GIP receptors sit on fat cells and in the brain as well as the pancreas, and the proposed contributions of the GIP arm include effects on insulin sensitivity and on how fat tissue handles energy. A 2022 study in The Lancet Diabetes & Endocrinology measured insulin secretion and sensitivity directly in adults with type 2 diabetes and reported gains in insulin sensitivity on tirzepatide larger than weight change alone would predict. Two receptors is not automatically double the effect; the head-to-head trial below is the honest measure.
What Is a GLP-1? Meaning, How GLP-1 Medications Work, and the List by Generic Name
GLP-1 medications list, by generic name
GLP-1 medications are named here by their generic, active-ingredient names. Brand names are deliberately left out.
| Generic name | Receptors | Notes | Prescribed by Pepti? |
|---|---|---|---|
| Semaglutide | GLP-1 | Once-weekly injection; an approved daily tablet also exists | Yes, as compounded dose-specific vials |
| Tirzepatide | GIP and GLP-1 (dual agonist) | Once-weekly injection | Yes, as compounded dose-specific vials |
| Liraglutide | GLP-1 | Once-daily injection | No |
| Dulaglutide | GLP-1 | An older GLP-1 medication with cardiovascular evidence | No |
| Exenatide | GLP-1 | An older GLP-1 peptide | No |
Liraglutide is the daily GLP-1 medication that a 2022 trial in JAMA (STEP 8) compared with weekly semaglutide, reporting greater weight loss with semaglutide. Dulaglutide is an older GLP-1 medication with its own cardiovascular evidence, and it was the comparator in SURPASS-CVOT, the tirzepatide heart-outcomes trial. Exenatide is an older GLP-1 peptide that appears in the stability literature. Pepti does not prescribe any of those three.
What is not a GLP-1
Several products people ask about alongside GLP-1 medications act through entirely different pathways and have much thinner evidence:
| Product | What it acts on instead |
|---|---|
| Tesamorelin | The growth hormone axis; studied for visceral fat |
| AOD-9604 | A fragment of growth hormone (amino acids 177 to 191); no appetite or incretin action |
| 5-Amino-1MQ | An enzyme inside fat cells; no appetite effect described |
| MOTS-c | A metabolic peptide described around muscle fuel handling |
| L-Carnitine | A nutrient adjunct, not an alternative |
None of them is a substitute for a GLP-1 medication, and none has human trial evidence comparable to semaglutide or tirzepatide. The best peptides for weight loss sets out where each fits.
What Is a GLP-1? Meaning, How GLP-1 Medications Work, and the List by Generic Name
GLP-1 medications at Pepti
Pepti prescribes two GLP-1 medications, both as compounded dose-specific vials. Each strength is a separate vial concentrated so that one weekly dose is a single draw, and a change in dose arrives as a new vial with new directions printed on it.
Semaglutide
Strength Vial Directions 0.25 mg weekly 1 mg in 1 mL (1 mg/mL) 0.25 mL (25 units) once weekly 0.5 mg weekly 2 mg in 2 mL (1 mg/mL) 0.50 mL (50 units) once weekly 1 mg weekly 4 mg in 2 mL (2 mg/mL) 0.50 mL (50 units) once weekly 1.7 mg weekly 7.5 mg in 3 mL (2.5 mg/mL) 0.68 mL (68 units) once weekly 2 mg weekly 10 mg in 2 mL (5 mg/mL) 0.40 mL (40 units) once weekly 2.5 mg weekly 10 mg in 2 mL (5 mg/mL) 0.50 mL (50 units) once weekly Semaglutide starts from $99 a month. The full reference is at what is semaglutide.
Tirzepatide
Strength Vial Directions 2.5 mg weekly 10 mg in 2 mL (5 mg/mL), with glycine 0.50 mL (50 units) once weekly 5 mg weekly 20 mg in 2 mL (10 mg/mL) 0.50 mL (50 units) once weekly 7.5 mg weekly 30 mg in 2 mL (15 mg/mL), with glycine 0.50 mL (50 units) once weekly 10 mg weekly 40 mg in 2 mL (20 mg/mL) 0.50 mL (50 units) once weekly 12.5 mg weekly 50 mg in 2 mL (25 mg/mL) 0.50 mL (50 units) once weekly 15 mg weekly 60 mg in 2 mL (30 mg/mL) 0.50 mL (50 units) once weekly Tirzepatide starts from $159 a month. Every strength is drawn at the same 0.50 mL, so when the dose changes, the vial changes and the line you draw to does not. Pepti's GLP-1 vials contain no B12. The full reference is at what is tirzepatide.
Each vial holds four weekly doses, which is why refills run every 28 days, one vial per fill. Both ship refrigerated with ice packs, with sterile syringes and alcohol prep pads, and your directions printed on the vial. Neither is offered as a pen. Your physician sets your strength and directions after reviewing your intake, and you never carry a unit count over from an earlier strength.
Semaglutide or tirzepatide?
In SURMOUNT-5, published in the New England Journal of Medicine in 2025, adults with obesity and no diabetes were randomised to the maximum tolerated dose of tirzepatide or semaglutide for 72 weeks, and tirzepatide produced greater average weight reduction. The trial was open-label, a real limitation. Semaglutide has the longer track record, cardiovascular and liver outcome trials (SELECT and ESSENCE), and the lower price. Gastrointestinal side effects are broadly similar. Which one suits you depends on your history, tolerance, goals and cost; the full comparison is in semaglutide vs tirzepatide. The two are never combined, because both act at the GLP-1 receptor.
What Is a GLP-1? Meaning, How GLP-1 Medications Work, and the List by Generic Name
Compounded vs approved GLP-1 medications
Semaglutide and tirzepatide are FDA-approved active ingredients, sold by their manufacturers as approved products in fixed-dose pens and tablets. A compounded GLP-1 is something different: the same active ingredient, prepared by a state-licensed pharmacy for an identified patient on a physician's prescription.
| Approved product | Compounded preparation | |
|---|---|---|
| Active ingredient | Semaglutide or tirzepatide | The same active ingredient |
| Who makes it | The manufacturer, under an approved application | A state-licensed pharmacy, to an individual prescription |
| FDA approved | Yes, as a finished product | No. Compounded medications are not FDA approved |
| Trial evidence | The STEP, SUSTAIN, SELECT, SURMOUNT and SURPASS programmes were run on these products | No trial has been run on any compounded preparation |
| Format | Fixed-dose pen or tablet | Multi-dose vial drawn with an insulin syringe |
| Quality assurance | Manufacturing standards and a stability programme | The pharmacy's sterile process and lot testing |
The molecule brings the pharmacology and the warnings, which transfer unchanged. The product brings the concentration, the added ingredients, the sterility and the label, and those depend on the pharmacy. That is why the questions to ask any provider are which pharmacy compounds it, whether it is semaglutide base rather than a salt form such as semaglutide sodium or acetate, what the concentration is, and what else is in the vial. Pepti's pharmacies are PCAB-accredited, FDA-registered US 503A compounding pharmacies, and lot test results are published at /quality/lab-results. The longer version is in is compounded semaglutide safe.
Why research-use GLP-1 vials are a different category
GLP-1 powders sold online "for research purposes" or "not for human consumption" are not compounded medication. No prescriber, no pharmacy and nobody accountable for identity, purity, sterility or concentration. With a GLP-1 that matters more than with most peptides, because the dose is titrated deliberately and a vial of unknown strength puts you somewhere on that curve you did not choose. The FDA has documented dosing errors with compounded injectable semaglutide in which people drew five to twenty times the intended amount. See research peptides vs prescription peptides.
What Is a GLP-1? Meaning, How GLP-1 Medications Work, and the List by Generic Name
Where GLP-1 compounding stands with the FDA
As of September 2026:
| Date | What happened |
|---|---|
| 2022 | Semaglutide and tirzepatide placed on the FDA drug shortage list, which allowed compounding of copies |
| 19 December 2024 | FDA reaffirmed that the tirzepatide shortage was resolved |
| 21 February 2025 | FDA declared the semaglutide shortage resolved |
| 18 February and 22 April 2025 | Shortage-based compounding ended for 503A pharmacies, for tirzepatide and semaglutide respectively |
| 30 April 2026 | FDA proposed excluding semaglutide, tirzepatide and liraglutide from the 503B bulks list; still a proposal as of September 2026 |
Shortage-based compounding has ended. What remains is the ordinary 503A pathway: a state-licensed pharmacy may compound for an identified patient where the prescriber determines and documents that a change in the compounded product produces a significant difference for that patient. The April 2026 proposal concerns 503B outsourcing facilities that compound in bulk; it does not by itself change the 503A framework. The FDA's consumer page on unapproved GLP-1 drugs, updated 1 September 2026, says compounded drugs are not FDA approved and have not been reviewed for safety, effectiveness or quality. Are peptides FDA approved explains the difference between not approved and not legal.
What Is a GLP-1? Meaning, How GLP-1 Medications Work, and the List by Generic Name
Side effects and who should not take a GLP-1
The most common side effects across the class are gastrointestinal: nausea, diarrhoea, vomiting, constipation and abdominal pain, most often in the days after a dose increase, which is why treatment starts at the lowest strength and steps up. Less common but important: pancreatitis, gallbladder disease, dehydration that can affect the kidneys, and low blood sugar when combined with insulin or a sulfonylurea. Slower gastric emptying can change how oral medications are absorbed, and tirzepatide can make oral contraceptives less reliable for four weeks after starting and after each dose increase. Managing nausea is covered in GLP-1 nausea: how to manage it.
| Situation | Why |
|---|---|
| Personal or family history of medullary thyroid carcinoma or MEN 2 | A contraindication for the class, based on thyroid C-cell tumours in rodent studies |
| History of pancreatitis | Needs careful discussion before any GLP-1 medication |
| Pregnancy, planning pregnancy, or breastfeeding | Not used |
| Type 1 diabetes | Not a GLP-1 indication |
| Taking insulin or a sulfonylurea | Raises the risk of low blood sugar; the full medication list matters |
| A planned surgery or sedation | Tell the anaesthesia team, because of slower gastric emptying |
Stop and contact your physician for severe or persistent abdominal pain, persistent vomiting, or any reaction that is severe, spreading or involves difficulty breathing.
What Is a GLP-1? Meaning, How GLP-1 Medications Work, and the List by Generic Name
What the evidence shows, honestly
Semaglutide and tirzepatide have the strongest evidence base of anything in this category: large randomised trials in obesity, type 2 diabetes, cardiovascular disease, liver disease and sleep apnoea, and wide clinical use. That is a genuine difference from peptides whose support is preclinical.
The caveat is specific. Every one of those trials used the manufacturers' products. Compounded semaglutide and tirzepatide share the active ingredient, not the trials and not the approval, and no provider should present a compounded vial as if it were the approved product. The withdrawal trials also matter: STEP 4 and SURMOUNT-4 reported most of the weight returning after people were switched to placebo, which is why GLP-1 treatment is planned as long-term with 28-day refills rather than as a short course. Trial averages describe groups, not any one person, and any provider quoting you an expected number is inventing it.
What Is a GLP-1? Meaning, How GLP-1 Medications Work, and the List by Generic Name
Where to get a GLP-1 prescribed
GLP-1 medications cannot be bought legitimately without a prescription. The prescription route:
- Complete a free online intake covering your history, medications and what you want help with.
- A physician licensed in your state reviews it, usually within 24 hours.
- If it is appropriate, a PCAB-accredited, FDA-registered US 503A pharmacy compounds it to that prescription. Lot test results are published at /quality/lab-results.
- It ships refrigerated with ice packs, sterile syringes and alcohol prep pads, with your directions printed on the vial.
- Your physician stays reachable for questions and dose changes, and refills run every 28 days, one vial per fill.
Pepti prescribes both in all 50 states and DC. Pepti is cash-pay and does not bill insurance. Step-by-step pages: how to get semaglutide prescribed online and how to get tirzepatide prescribed online.
References
What this is based on.
References
- Wilding JPH, Batterham RL, Calanna S, et al.. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1) · New England Journal of Medicine (2021) · PMID 33567185
- Lincoff AM, Brown-Frandsen K, Colhoun HM, et al.. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT) · New England Journal of Medicine (2023) · PMID 37952131
- Wadden TA, Bailey TS, Billings LK, et al.. Effect of subcutaneous semaglutide vs placebo as an adjunct to intensive behavioral therapy on body weight in adults with overweight or obesity (STEP 3) · JAMA (2021) · PMID 33625476
- Rubino D, Abrahamsson N, Davies M, et al.. Effect of Continued Weekly Subcutaneous Semaglutide vs Placebo on Weight Loss Maintenance in Adults With Overweight or Obesity: The STEP 4 Randomized Clinical Trial · JAMA (2021) · PMID 33755728
- Marso SP, Bain SC, Consoli A, et al.. Semaglutide and Cardiovascular Outcomes in Patients with Type 2 Diabetes (SUSTAIN-6) · New England Journal of Medicine (2016) · PMID 27633186
- Davies M, Færch L, Jeppesen OK, et al.. Semaglutide 2.4 mg once a week in adults with overweight or obesity, and type 2 diabetes (STEP 2): a randomised, double-blind, double-dummy, placebo-controlled, phase 3 trial · The Lancet (2021) · PMID 33667417
- Garvey WT, Batterham RL, Bhatta M, et al.. Two-year effects of semaglutide in adults with overweight or obesity: the STEP 5 trial · Nature Medicine (2022) · PMID 36216945
- Rubino DM, Greenway FL, Khalid U, et al.. Effect of Weekly Subcutaneous Semaglutide vs Daily Liraglutide on Body Weight in Adults With Overweight or Obesity Without Diabetes: The STEP 8 Randomized Clinical Trial · JAMA (2022) · PMID 35015037
- Aronne LJ, Horn DB, le Roux CW, et al.. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5) · New England Journal of Medicine (2025) · PMID 40353578
- Sanyal AJ, Newsome PN, Kliers I, et al.. Phase 3 Trial of Semaglutide in Metabolic Dysfunction-Associated Steatohepatitis (ESSENCE) · New England Journal of Medicine (2025) · PMID 40305708
- Wilding JPH, Batterham RL, Davies M, Van Gaal LF, Kandler K et al.. Weight regain and cardiometabolic effects after withdrawal of semaglutide: The STEP 1 trial extension · Diabetes Obes Metab (2022) · PMID 35441470
- Batsis JA, Gavras A, Gross DC, Cheever CR, Da Silva BR et al.. Effect of Incretin-Based and Nonpharmacologic Weight Loss on Body Composition: A Systematic Review · Ann Intern Med (2026) · PMID 41996180
Citations are provided for educational purposes. They do not constitute medical advice. Always discuss any peptide protocol with your prescribing physician.
Common questions
What Is a GLP-1? Meaning, How GLP-1 Medications Work, and the List by Generic Name, answered.
GLP-1, glucagon-like peptide-1, is a hormone released by the small intestine after a meal. It triggers insulin release when blood glucose is high, lowers glucagon, slows stomach emptying and signals fullness to the brain. It is broken down within minutes, so medications that mimic it are modified to last for days.
Glucagon-like peptide-1. It is a peptide hormone from the gut and one of two incretin hormones; the other is GIP, glucose-dependent insulinotropic polypeptide.
A GLP-1 medication, or GLP-1 receptor agonist, is a drug that activates the same receptor as the natural hormone but lasts far longer. "GLP-1" is shorthand for the class.
Mainly through appetite. GLP-1 receptors in the hypothalamus and brainstem regulate hunger and fullness, and slower stomach emptying makes fullness last longer after a meal. People eat less over a long period, and the change in weight in the trials follows from that. It is not a stimulant.
By generic name: semaglutide, tirzepatide (a dual GIP/GLP-1 agonist), liraglutide, dulaglutide and exenatide. Pepti prescribes compounded semaglutide and compounded tirzepatide.
Yes, and more. It activates the GLP-1 receptor and the GIP receptor, which is why it is called a dual agonist. Semaglutide acts on the GLP-1 receptor only.
It contains the same active ingredient, but it is a different product. The approved products are manufactured under an approved application and were used in every trial; a compounded preparation is made by a state-licensed pharmacy for an individual prescription and is not FDA approved.
Yes, on an individual prescription. Shortage-based compounding ended in 2025, and a 503A pharmacy now compounds for an identified patient where the prescriber documents a clinical reason. The FDA's April 2026 proposal concerns 503B bulk outsourcing facilities and was still pending as of September 2026.
Semaglutide starts from $99 a month and tirzepatide from $159 a month, rising with the strength. Each price is all-in, covering medication, physician review, refill management and shipping.
No. Both act at the GLP-1 receptor, so combining them adds side effects without adding a mechanism. Switching from one to the other is a decision made with your physician.
The withdrawal trials for both medications reported most of the weight returning over the following year in people switched to placebo. GLP-1 medications work while they are being taken, which is why treatment is planned as ongoing.
No. Bloodwork is not required for any Pepti treatment. If your physician wants labs for your care, they'll ask through your account. The free assessment goes to a physician licensed in your state. A consultation does not guarantee a prescription.
Next step
See what a physician recommends for you.
A licensed physician in your state reviews your intake and decides what is appropriate. A consultation does not guarantee a prescription.