How GLP-1 Agonists Work
The Incretin Pathway
GLP-1 Receptor Activation
GLP-1 (Glucagon-Like Peptide-1) is an incretin hormone released from the gut after eating. It enhances insulin secretion, suppresses glucagon, and slows gastric emptying to promote satiety.
Appetite Suppression
GLP-1 agonists activate hypothalamic receptors that reduce hunger and food noise. Users report feeling fuller faster and having less craving for high-calorie foods.
Slowed Gastric Emptying
By delaying stomach emptying, GLP-1 agonists extend the feeling of fullness after meals, reducing overall caloric intake throughout the day.
Beta Cell Preservation
GLP-1 agonists enhance pancreatic beta cell function and may protect against beta cell apoptosis.
Liraglutide
Saxenda / Victoza
The original FDA-approved weight management GLP-1 agonist. Daily injection with proven long-term outcomes.
Daily Injection
Requires daily subcutaneous injection. Some users prefer the routine consistency; others find weekly options more convenient.
LEADER Trial (CV Benefit)
13% reduction in major adverse cardiovascular events (MACE) vs placebo (hazard ratio 0.87) over a median 3.8 years (PMID 27295427).
Dual FDA Approval
Approved for both type 2 diabetes (Victoza, 2010) and chronic weight management (Saxenda, 2014).
SCALE Trial Data
SCALE Obesity & Prediabetes: 8.4 kg mean weight loss vs 2.8 kg with placebo at 56 weeks, from a 106.2 kg average start (PMID 26132939). SCALE Maintenance: a further 6.2% vs 0.2% with placebo after a low-calorie-diet run-in (PMID 23812094).
💉 Liraglutide Dosing Schedule (Saxenda)
1 Week 1: 0.6mg daily (starting dose)
2 Week 2: 1.2mg daily
3 Week 3: 1.8mg daily
4 Week 4: 2.4mg daily
5 Week 5 onward: 3mg daily (maintenance; lower doses are for titration only — Saxenda label)
Dulaglutide
Trulicity
Weekly GLP-1 injection using Fc fusion technology for extended half-life. Primarily diabetes-focused with strong CV data.
Fc Fusion Technology
Dulaglutide combines two GLP-1 analog molecules with an Fc fragment, creating a large molecule with a long half-life that allows weekly dosing.
Weekly Convenience
Single weekly injection provides full therapeutic effect. Less injection burden than daily liraglutide, though not approved for weight loss indication.
REWIND Trial (CV Benefit)
12% reduction in MACE cardiovascular events. Notably, REWIND enrolled more patients with lower baseline cardiovascular risk than other GLP-1 CVOTs.
Weight Loss Indication?
Trulicity is NOT approved for weight management — only type 2 diabetes. This is a key distinction vs Saxenda (liraglutide) and Wegovy (semaglutide).
💉 Dulaglutide Dosing Schedule (Trulicity)
1 Week 1-4: 0.75mg weekly (starting dose)
2 Week 5+: 1.5mg weekly (standard maintenance)
3 Higher doses (3mg, 4.5mg) available for enhanced glycemic control
Cross-Trial Comparison
GLP-1 Agonist Comparison
Comparing all four major GLP-1 based therapies: Liraglutide, Dulaglutide, Semaglutide, and Tirzepatide.
| Drug | Dosing | Weight Loss | A1C Reduction | CV Benefit | Obesity Approval |
|---|---|---|---|---|---|
|
Daily
Liraglutide
|
Daily | ~8% | -1.36% (AWARD-6, 1.8mg) | 13% (LEADER) | ✅ Yes (Saxenda) |
|
Weekly
Dulaglutide
|
Weekly | — (not approved for weight) | -1.42% (AWARD-6) | 12% (REWIND) | ❌ No |
|
Weekly
Semaglutide
|
Weekly | 14.9% (STEP 1, 68 wk) | — | 20% (SELECT) | ✅ Yes (Wegovy) |
|
New
Tirzepatide
|
Weekly | 20.9% (SURMOUNT-1, 15 mg, 72 wk) | — | Noninferior to dulaglutide (SURPASS-CVOT) | ✅ Yes (Zepbound) |
Why Newer GLP-1s Dominate
Why Semaglutide & Tirzepatide Took Over
Larger Average Weight Loss
In separate placebo-controlled trials, tirzepatide 15 mg produced −20.9% at 72 weeks (SURMOUNT-1, PMID 35658024) and semaglutide 2.4 mg −14.9% at 68 weeks (STEP 1, PMID 33567185), vs about 8% (8.4 kg) for liraglutide 3 mg in SCALE. These are not head-to-head comparisons.
Better Dosing Convenience
Weekly semaglutide and tirzepatide beat daily liraglutide on convenience. One injection a week instead of seven.
Oral Option Exists
Semaglutide comes as a pill: Rybelsus for type 2 diabetes, and Wegovy tablets for weight management (approved December 2025). Liraglutide and dulaglutide have no pill version. A non-peptide oral GLP-1, orforglipron (Foundayo), was also approved in April 2026 (Drugs@FDA NDA 220934).
Latest CV Data
SURPASS-CVOT compared tirzepatide head-to-head with dulaglutide (not placebo) in 13,165 people with type 2 diabetes and atherosclerotic cardiovascular disease: MACE 12.2% vs 13.1% (hazard ratio 0.92), noninferior but not statistically superior (PMID 41406444). Semaglutide's SELECT trial cut MACE 20% vs placebo in obesity without diabetes (PMID 37952131).
When to Choose Established GLP-1s
Why Older GLP-1s Are Still Right for Some
These drugs aren't obsolete. For many patients, liraglutide or dulaglutide remain excellent choices based on individual circumstances. The "best" GLP-1 is the one that works for your specific situation.
Insurance & formulary
Coverage varies by plan. If your formulary prefers liraglutide (including generics) or dulaglutide, your copay may be lower than for newer drugs; check your plan.
Availability
Check supply before you plan around liraglutide. As of September 2026 the FDA lists liraglutide injection as in shortage, with Saxenda and Victoza in limited availability and Saxenda due to be discontinued in January 2027. Generic liraglutide is listed as available from several makers.
Side Effect Tolerance
Daily dosing allows small weekly dose steps (0.6 mg at a time for Saxenda). In AWARD-6, GI side effects were similar for weekly dulaglutide and daily liraglutide (PMID 25018121).
Diabetes-Only Indication
For patients with type 2 diabetes who don't need weight loss medication, dulaglutide provides excellent glycemic control without the "weight loss drug" label or costs.
Safety Profile
Side Effects & Warnings
Liraglutide (Saxenda 3mg) Common Side Effects
Adults in Saxenda trials vs placebo: nausea 39.3% vs 13.8%, diarrhea 20.9% vs 9.9%, constipation 19.4% vs 8.5%, vomiting 15.7% vs 3.9% (Saxenda label).
Dulaglutide (1.5mg) Common Side Effects
AWARD-6, 26 weeks: nausea 20%, diarrhea 12%, vomiting 7% with dulaglutide 1.5mg (vs 18%, 12%, 8% with liraglutide 1.8mg) (PMID 25018121).
Ideal Candidates
Who Should Consider These GLP-1s?
✅ Great Fit For
- Patients with type 2 diabetes seeking glycemic control
- Those with insurance that covers liraglutide/dulaglutide
- Those preferring daily routine for consistency
- Patients who tolerate higher-dose weekly GLP-1s poorly
- Anyone needing a gradual titratable approach
⚠️ Consider Other Options
- Those wanting once-weekly dosing with a weight-management indication
- Patients prioritizing greater average weight loss
- Those wanting oral medication option (semaglutide)
- Anyone with contraindications to GLP-1 class
References
Key Clinical Trials
SCALE Obesity & Prediabetes
A Randomized, Controlled Trial of 3.0 mg of Liraglutide in Weight Management (SCALE Obesity and Prediabetes)
PMID: 26132939
SCALE Maintenance
Weight maintenance and additional weight loss with liraglutide after low-calorie-diet-induced weight loss
PMID: 23812094
SURPASS-CVOT
Cardiovascular Outcomes with Tirzepatide versus Dulaglutide in Type 2 Diabetes
PMID: 41406444
🛒 Related Products
Essential supplies for GLP-1 injection protocols
💉 Insulin Syringes 29G
Precision dosing for GLP-1 injections
🧻 Alcohol Swabs
Pre-injection skin preparation
🗑️ Sharps Container
Safe needle disposal container
⚖️ Digital Precision Scale
Track weight loss progress accurately
📏 Body Measuring Tape
Track inches lost beyond scale weight
🩸 Glucose Monitor
Monitor blood sugar during GLP-1 therapy
Affiliate links — support HighPeptides at no extra cost.
📚
Want the Complete Protocol Guide?
Dosing schedules, interaction warnings, and cycle protocols for 50+ compounds — all in one place.
Get the Guide — $19 (normally $29) →
New to peptides? Start with the $19 Buyer’s Playbook →
⚠️ Medical Disclaimer
This content is for educational purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider before starting, stopping, or modifying any medication or supplementation protocol. GLP-1 agonists carry risks including pancreatitis, thyroid tumors, and severe gastrointestinal events. Individual results vary based on diet, exercise, genetics, and other factors.
📘
Get the Free 2026 Peptide Protocol Stack
Twelve compounds across four pillars — metabolic, tissue repair, longevity, cognitive. Citations included, formatted to print. Sent straight to your inbox.