Semaglutide vs Tirzepatide vs Retatrutide: Weight Loss Percentages and Mechanisms Compared

Three Compounds, Three Receptor Profiles

The incretin class has expanded rapidly. Semaglutide, tirzepatide, and retatrutide represent three different approaches to modulating the body’s incretin signaling — each with a different receptor profile and a different efficacy magnitude.

Semaglutide — single receptor agonism at GLP-1.

Tirzepatide — dual receptor agonism at GLP-1 and GIP.

Retatrutide — triple receptor agonism at GLP-1, GIP, and glucagon.

The progression from one to three receptor targets corresponds roughly — but not perfectly — to efficacy magnitude.

 

Weight Loss Percentages: The Real Data

Based on the pivotal clinical trial datasets:

Semaglutide (2.4 mg weekly, Wegovy dosing): Approximately 15% mean body weight reduction at 68 weeks in the STEP program.

Tirzepatide (15 mg weekly, Zepbound dosing): Approximately 20–22% mean body weight reduction at 72 weeks in the SURMOUNT program.

Retatrutide (12 mg weekly): Approximately 24% mean body weight reduction at 48 weeks in the phase 2 trial. This figure made retatrutide a headline story when published.

These numbers are direct comparisons at the highest tested doses in the respective pivotal datasets. Lower doses produce proportionally smaller effects. Cross-trial comparisons always require caveats around trial population differences, duration, and titration schedules.

 

Mechanism Differences

GLP-1 receptor agonism (all three): Slowed gastric emptying, enhanced glucose-dependent insulin secretion, suppression of glucagon release, central effects on appetite.

GIP receptor agonism (tirzepatide, retatrutide): Additive effects on insulin secretion, different central appetite regulation pathway, potentially different adipose tissue effects.

Glucagon receptor agonism (retatrutide only): Increased energy expenditure — glucagon agonism drives hepatic lipolysis and thermogenesis. This additional mechanism likely explains part of retatrutide’s weight loss magnitude advantage.

 

The “GLP-3” Framing

Patients sometimes ask: “Is retatrutide a GLP-3?” The naming convention is worth clarifying. GLP-3 is not a formal receptor class. Retatrutide is best described as a triple receptor agonist at GLP-1, GIP, and glucagon — not as “GLP-3.” The “GLP-3” terminology appears in informal sources but is not pharmacologically correct.

 

Side Effect Profiles

The side effect profiles of these three compounds are broadly similar in character — predominantly gastrointestinal (nausea, vomiting, diarrhea, constipation) — with some differences in magnitude and in specific issues:

Semaglutide. GI symptoms at initiation are common; usually manageable with titration.

Tirzepatide. Similar GI profile; some patients experience somewhat better tolerability.

Retatrutide. GI effects appear comparable; the glucagon receptor addition has theoretically different effects on glycemic control that require careful observation in practice.

All three require attention to:

• Gallbladder-related considerations
• Pancreatitis risk in susceptible individuals
• Thyroid C-cell considerations (MTC contraindication)
• Muscle mass preservation in weight loss

 

Selection Framework

A reasonable framework for matching patient to therapy:

Semaglutide. Established first-line, well-characterized, meaningful weight loss. Appropriate for many patients, particularly when cost or access favors semaglutide.

Tirzepatide. When semaglutide is inadequate, when the patient prioritizes weight loss magnitude, or when the patient has specific metabolic markers (glycemic control challenges) that favor the dual receptor profile.

Retatrutide. Not yet commercially available. Patients asking about it should be counseled on the regulatory situation and redirected to available therapies.

 

The Compounded-Peptide Context

For physicians operating in the peptide-informed practice space, it’s worth noting that peptides like CJC-1295, ipamorelin, AOD-9604, and related compounds target different aspects of body composition than the incretin class. They are not pharmacologically equivalent. The peptide class supports body composition quality (lean mass preservation, recovery, body composition during weight loss); the incretin class drives absolute weight loss magnitude. In practice, combined protocols are increasingly common.

 

Key Takeaways

• Semaglutide, tirzepatide, and retatrutide represent progressive receptor-class expansion and increasing weight loss efficacy.
• Weight loss percentages at highest doses: semaglutide ~15%, tirzepatide ~20–22%, retatrutide ~24%.
• Retatrutide’s additional glucagon agonism likely explains part of the efficacy advantage.
• “GLP-3” is not a formal receptor class; retatrutide is a triple agonist.
• Side effect profiles are broadly similar in character across the class.
• Retatrutide is not yet commercially available; patients should be counseled accordingly.

 

Frequently Asked Questions

Is tirzepatide a GLP-1?

Tirzepatide is a dual agonist at GLP-1 and GIP receptors. It includes GLP-1 activity but is not exclusively a GLP-1.

Is retatrutide a GLP-3?

No. Retatrutide is a triple agonist at GLP-1, GIP, and glucagon receptors. “GLP-3” is not a formal pharmacological classification.

Which has the most weight loss?

Retatrutide has shown the highest weight loss percentages in clinical trials, followed by tirzepatide, then semaglutide.

What about combining these with peptides like CJC-1295 / ipamorelin?

Combined protocols are increasingly common in physician practice, targeting different aspects of body composition.

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