GLP-1 Peptides for Weight Loss: Every Compound Explained

What is GLP-1?

Glucagon-like peptide-1 (GLP-1) is an incretin hormone produced in the L-cells of the small intestine after eating. It signals the brain to reduce appetite, tells the stomach to slow down, and enhances insulin release from the pancreas. GLP-1 receptor agonists are synthetic versions of this hormone, engineered to last much longer in the body.

Natural GLP-1 has a half-life of about 2 minutes — it is rapidly broken down by the enzyme DPP-4. Medications like semaglutide are modified to resist DPP-4 and bind to albumin in the blood, extending the half-life to 7 days. This is what enables once-weekly dosing.

The GLP-1 family: Single, dual, and triple agonists

The field has evolved from single-receptor to multi-receptor approaches. Each generation targets additional hormonal pathways for greater metabolic effect:

Single agonists (GLP-1 only)

These activate only the GLP-1 receptor. They reduce appetite and slow gastric emptying but do not directly increase energy expenditure.

• Semaglutide (Wegovy/Ozempic) — 14.9% weight loss, weekly injection, FDA-approved
• Liraglutide (Saxenda/Victoza) — 8% weight loss, daily injection, FDA-approved

Dual agonists (GLP-1 + one additional receptor)

These activate two receptors for enhanced metabolic effects:

• Tirzepatide (Zepbound/Mounjaro) — GIP + GLP-1, 20.9% weight loss, FDA-approved
• Survodutide — Glucagon + GLP-1, 19.2% weight loss, Phase 3 trials
• CagriSema — Amylin analog + semaglutide combination, Phase 3 trials

Triple agonists (GLP-1 + two additional receptors)

• Retatrutide — GIP + GLP-1 + Glucagon, 24.2% weight loss, Phase 3 trials

Head-to-head comparison: Every GLP-1 agonist

For detailed side-by-side comparisons, see: Semaglutide vs Tirzepatide | Semaglutide vs Retatrutide | Tirzepatide vs Retatrutide | Semaglutide vs Liraglutide

How GLP-1 agonists work: The science

Appetite regulation

GLP-1 agonists act on the hypothalamus — the brain region that controls hunger and satiety. They activate POMC/CART neurons (which signal "stop eating") and inhibit NPY/AgRP neurons (which signal "eat more"). The result is a significant reduction in hunger, cravings, and what many people describe as "food noise" — the constant background thinking about food.

Gastric emptying

GLP-1 slows the rate at which food moves from the stomach into the small intestine by 10-30%. This means you feel full longer after eating. It is also the primary cause of the nausea that some people experience — the stomach is holding food longer than it is used to.

Insulin and blood sugar

GLP-1 agonists enhance glucose-dependent insulin secretion — meaning they help your pancreas release insulin more effectively when blood sugar rises, but do not cause insulin release when blood sugar is already normal. This makes hypoglycemia (dangerously low blood sugar) rare unless combined with other diabetes medications.

Cardiovascular effects

The SELECT trial demonstrated that semaglutide reduces major adverse cardiovascular events by 20% in overweight/obese adults with established cardiovascular disease. This cardiovascular benefit appears to be a class effect — not just a side benefit of weight loss.

Side effects by compound

*Retatrutide data from Phase 2 (smaller sample). Phase 3 data pending.

GI side effects are dose-dependent and improve with slow titration. Most people who discontinue these medications for side effects do so during the dose escalation period, not after reaching their maintenance dose.

Read more: GLP-1 Side Effects: What to Expect

The weight regain problem

All GLP-1 medications show significant weight regain after discontinuation. This is the most important thing to understand about these medications: they are not a temporary fix.

• Semaglutide (STEP 4): Two-thirds of lost weight regained within 1 year of stopping
• Tirzepatide (SURMOUNT-4): 14% body weight regain after switching to placebo

This does not mean the medications do not work — it means obesity is a chronic condition that requires ongoing treatment, similar to high blood pressure or high cholesterol. The medications manage the condition; they do not cure it.

Cost and access

Insurance coverage is the biggest variable. Some plans cover Wegovy but not Zepbound, or vice versa. Manufacturer savings cards, compounding pharmacies, and patient assistance programs can reduce costs.

Useful tools

• Peptide Dosage Calculator — Calculate injection volumes
• Reconstitution Calculator — Calculate concentrations and doses per vial
• All Comparisons — Side-by-side compound comparisons
• Peptide Stacks — Protocol combinations

Further reading

• Peptides for Weight Loss: The Complete Guide
• Best GLP-1 for Weight Loss in 2026: Every Option Ranked
• Semaglutide Weight Loss Results Week by Week
• Tirzepatide Before and After 3 Months: What the Data Shows
• Retatrutide Phase 2 Results: What 24% Weight Loss Means
• Semaglutide vs Tirzepatide: What the Research Says
• Oral vs Injectable Semaglutide: Which Works Better?
• GLP-1 Side Effects: What to Expect
• Do GLP-1 Medications Cause Muscle Loss?
• New Weight Loss Peptides in 2026: Pipeline Update
• Best Peptides for Weight Loss (Goal Page)

FAQ

What is a GLP-1 receptor agonist?

A GLP-1 receptor agonist is a medication that mimics the hormone glucagon-like peptide-1, which your body naturally produces after eating. By activating GLP-1 receptors, these medications reduce appetite, slow gastric emptying, improve insulin sensitivity, and promote weight loss. Examples include semaglutide (Wegovy/Ozempic) and tirzepatide (Zepbound/Mounjaro).

Which GLP-1 is best for weight loss?

Among FDA-approved options, tirzepatide (Zepbound) produces the most weight loss — 20.9% average in SURMOUNT-1, and 20.2% in a direct head-to-head against semaglutide (13.7%) in SURMOUNT-5. However, individual responses vary, insurance coverage differs, and some people tolerate one better than the other.

How do GLP-1 medications cause weight loss?

GLP-1 medications work through multiple pathways: they activate satiety neurons in the hypothalamus (reducing hunger), slow gastric emptying (you feel full longer), and improve insulin sensitivity (better metabolic function). The net effect is a significant reduction in caloric intake.

Are GLP-1 medications safe long-term?

Clinical trials of 1-3 years show acceptable safety profiles. The SELECT trial (17,604 participants, 33-month follow-up) showed semaglutide reduced cardiovascular events by 20%. Common side effects are GI-related and typically improve. Rare risks include pancreatitis and gallbladder events.

What is the difference between single, dual, and triple agonists?

Single agonists (semaglutide, liraglutide) activate only GLP-1 receptors. Dual agonists (tirzepatide) activate GLP-1 and GIP for enhanced metabolic effects. Triple agonists (retatrutide) add glucagon for increased energy expenditure. Each additional receptor generally produces greater weight loss.

Sources

1. STEP 1 — Semaglutide for weight management (NEJM, 2021; PMID: 33567185)
2. SURMOUNT-1 — Tirzepatide for obesity (NEJM, 2022; PMID: 35658024)
3. SURMOUNT-5 — Tirzepatide vs semaglutide (NEJM, 2024; PMID: 39652484)
4. Retatrutide Phase 2 (NEJM, 2023; PMID: 37351564)
5. SELECT — Semaglutide cardiovascular outcomes (NEJM, 2023; PMID: 37952131)
6. SCALE — Liraglutide for weight management (NEJM, 2015; PMID: 26132939)
7. Survodutide Phase 2 (NEJM, 2024; PMID: 38587239)