Semaglutide vs Tirzepatide vs Retatrutide: Weight Loss Peptides Compared

TL;DR: Semaglutide (Wegovy) produces ~15% weight loss and is the most established option with the longest safety track record. Tirzepatide (Zepbound) produces ~22.5% weight loss with its dual GLP-1/GIP mechanism and is FDA-approved. Retatrutide is the most potent at ~28.7% weight loss through triple-agonism (GLP-1/GIP/glucagon), but remains investigational. Choose semaglutide for proven safety, tirzepatide for stronger results with FDA approval, or research-grade retatrutide for maximum weight loss with the understanding that it's not yet approved.

What Are These Peptides?

All three belong to the incretin-based class of weight loss medications, but each activates a different combination of metabolic receptors:

Semaglutide (brand names: Wegovy for weight loss, Ozempic for diabetes) is a GLP-1 receptor agonist. It mimics the gut hormone GLP-1 to reduce appetite, slow gastric emptying, and improve blood sugar regulation. FDA-approved for chronic weight management in 2021, it was the first of the modern weight loss peptides and remains the most widely prescribed.

Tirzepatide (brand names: Zepbound for weight loss, Mounjaro for diabetes) is a dual GLP-1 and GIP receptor agonist. By activating both incretin pathways simultaneously, it produces stronger appetite suppression and metabolic effects than GLP-1 alone. FDA-approved for weight loss in 2023.

Retatrutide (Eli Lilly, investigational) is a triple-agonist that activates GLP-1, GIP, and glucagon receptors. The addition of glucagon receptor activation increases energy expenditure and fat oxidation beyond what the dual-agonist approach achieves. Currently in Phase 3 clinical trials with no FDA approval date set.

How They Work

Semaglutide: Single Agonist (GLP-1)

Activates GLP-1 receptors in the brain to reduce appetite and increase satiety
Slows gastric emptying, making meals feel more filling for longer
Improves pancreatic insulin secretion and blood sugar control
Weekly subcutaneous injection

Tirzepatide: Dual Agonist (GLP-1 + GIP)

Activates both GLP-1 and GIP receptors simultaneously
GIP receptor activation enhances fat metabolism and insulin sensitivity beyond GLP-1 alone
Stronger appetite suppression through dual incretin signaling
May improve body composition (ratio of fat loss to lean mass loss) compared to GLP-1 alone
Weekly subcutaneous injection

Retatrutide: Triple Agonist (GLP-1 + GIP + Glucagon)

Activates GLP-1, GIP, and glucagon receptors simultaneously
Glucagon component increases resting energy expenditure and hepatic fat oxidation
Dramatic liver fat reduction (up to 82.4% in Phase 2 trials)
May address metabolic dysfunction beyond weight loss
Weekly subcutaneous injection

Clinical Results Comparison

Metric	Semaglutide (Wegovy)	Tirzepatide (Zepbound)	Retatrutide
Max weight loss	~14.9% (68 weeks)	~22.5% (72 weeks)	~28.7% (68 weeks)
Mechanism	GLP-1	GLP-1 + GIP	GLP-1 + GIP + Glucagon
Max dose	2.4 mg/week	15 mg/week	12 mg/week
Key trial	STEP 1 (2021)	SURMOUNT-1 (2022)	TRIUMPH-3/4 (2025)
Trial size	1,961 participants	2,539 participants	1,200+ participants
FDA status	Approved (2021)	Approved (2023)	Investigational (Phase 3)
Availability	Prescription	Prescription	Research peptide only
Liver fat reduction	Modest	Moderate	Up to 82.4%
Discontinuation rate	~7%	~6-14%	12-18%
Administration	Weekly SubQ	Weekly SubQ	Weekly SubQ

Weight Loss Trajectory

Semaglutide: Gradual, steady weight loss reaching a plateau around 60-68 weeks. The STEP 1 trial showed consistent loss throughout, with the 2.4mg dose producing 14.9% mean body weight reduction.

Tirzepatide: Faster and deeper weight loss. The SURMOUNT-1 trial showed the 15mg dose achieving 22.5% at 72 weeks, with the curve still declining — suggesting the maximum effect may not have been reached.

Retatrutide: The most aggressive weight loss curve of any studied medication. Phase 2 data showed 24.2% at 48 weeks with no plateau. Phase 3 (TRIUMPH-3) confirmed 28.7% at 68 weeks at the 12mg dose, approaching results previously only achievable through bariatric surgery.

Side Effects Compared

Shared GI Side Effects (All Three)

Nausea, vomiting, diarrhea, and constipation are the most common side effects across all three medications. These are dose-related, typically worst during escalation periods, and improve over time as the body adjusts.

Semaglutide-Specific

Most established safety profile (5+ years of post-market data)
Lower discontinuation rates than the other two
Gallbladder events (gallstones, cholecystitis) associated with rapid weight loss
Small heart rate increase (1-3 bpm)

Tirzepatide-Specific

GI side effects may be slightly more intense during escalation than semaglutide
Similar gallbladder and heart rate considerations
Post-market reports still accumulating (approved 2023)

Retatrutide-Specific

Dysesthesia — abnormal skin sensations (tingling, burning, heightened sensitivity) affecting ~21% of participants at 12mg. This side effect is unique to retatrutide and not seen with semaglutide or tirzepatide. Generally mild and rarely caused discontinuation.
Higher discontinuation rates (12-18% vs 6-7% for semaglutide)
Some participants discontinued because weight loss was too rapid, not due to side effects
Limited safety data compared to the approved medications

All Three: Important Safety Considerations

Thyroid: All carry a boxed warning for medullary thyroid carcinoma (MTC) risk based on rodent studies. Contraindicated with personal/family history of MTC or MEN 2.
Pancreatitis: Monitored as a class concern, no definitive signal in any trial
Lean mass loss: All weight loss interventions cause some lean mass loss alongside fat. Resistance training and adequate protein are recommended.
Pregnancy: Should not be used during pregnancy. Discontinue well before planned pregnancy.
Weight regain: All three show weight regain after discontinuation — these are maintenance medications, not cures.

Which Should You Choose?

Choose Semaglutide If:

You want the most established safety profile with 5+ years of real-world data
You need a prescription option available through standard healthcare channels
Moderate weight loss (10-15%) is sufficient for your goals
You have type 2 diabetes (also approved as Ozempic for blood sugar management)
You prefer the most extensively studied option

Choose Tirzepatide If:

You want stronger weight loss (~22%) with FDA approval and prescription availability
Semaglutide was insufficient or you plateaued on GLP-1 monotherapy
You want potential body composition benefits from dual-agonism
You're comfortable with a newer medication (approved 2023, less post-market data)

Choose Retatrutide If:

You're seeking the maximum possible weight loss from a peptide
You have significant liver fat — retatrutide's glucagon component produces dramatic hepatic fat reduction
You understand it's investigational with limited human safety data
You're comfortable sourcing research-grade peptides outside the prescription system
You've been informed about the dysesthesia risk unique to this compound

Availability and Cost

Semaglutide (Wegovy): Prescription. Widely available through pharmacies. List price ~$1,300/month, often covered by insurance for qualifying patients. Generic versions may be available in some markets.

Tirzepatide (Zepbound): Prescription. Available through pharmacies. List price ~$1,060/month, insurance coverage expanding. Compounding pharmacy versions may be available at lower cost.

Retatrutide: Not approved. Available only as a research peptide. The FDA has warned about unapproved GLP-1 products being marketed without proper standards. If sourcing research-grade retatrutide, look for suppliers with third-party HPLC testing and published certificates of analysis.

Frequently Asked Questions

Which causes more weight loss, semaglutide or tirzepatide?

Tirzepatide produces more weight loss than semaglutide. In clinical trials, tirzepatide (Zepbound) achieved approximately 22.5% body weight loss at 72 weeks compared to semaglutide's (Wegovy) approximately 14.9% at 68 weeks. Tirzepatide's dual GLP-1 and GIP mechanism provides stronger appetite suppression and metabolic effects.

What is retatrutide and how does it compare to semaglutide?

Retatrutide is a triple-agonist investigational peptide that activates GLP-1, GIP, and glucagon receptors simultaneously. In Phase 2 trials, it produced approximately 24.2% weight loss at 48 weeks, exceeding semaglutide's maximum effect in a shorter timeframe. Phase 3 data at 68 weeks showed 28.7% weight loss. It is not yet FDA-approved.

Is retatrutide better than tirzepatide for weight loss?

Based on available trial data, retatrutide produces more weight loss than tirzepatide — approximately 28.7% at 68 weeks versus 22.5% at 72 weeks. However, retatrutide is still investigational (Phase 3 trials), while tirzepatide is FDA-approved and available by prescription. Direct head-to-head trials have not been conducted.

What are the side effects of semaglutide vs tirzepatide vs retatrutide?

All three share GI side effects (nausea, vomiting, diarrhea) that are most common during dose escalation and typically improve over time. Retatrutide has a unique side effect — dysesthesia (abnormal skin sensations) in about 21% of participants at the highest dose — not seen with the other two. Tirzepatide and retatrutide have higher discontinuation rates than semaglutide.

Can you buy retatrutide?

Retatrutide is not FDA-approved and is not available by prescription. It is available as a research peptide from select suppliers. The FDA has warned about unapproved GLP-1 products being marketed without proper manufacturing standards. If sourcing research-grade retatrutide, look for suppliers with third-party testing and published certificates of analysis.

Sources

Wilding, J.P.H., et al. (2021). Once-Weekly Semaglutide in Adults with Overweight or Obesity. New England Journal of Medicine, 384, 989-1002. (STEP 1 trial)
Jastreboff, A.M., et al. (2022). Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine, 387, 205-216. (SURMOUNT-1 trial)
Jastreboff, A.M., et al. (2023). Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. New England Journal of Medicine, 389, 514-526.
Eli Lilly. (2025). TRIUMPH-3 Phase 3 Results: Retatrutide in Adults with Obesity. Press release and conference presentation.
Rosenstock, J., et al. (2023). Retatrutide, a GIP, GLP-1, and Glucagon Receptor Agonist, for People with Type 2 Diabetes: A Randomised, Double-Blind, Placebo and Active-Comparator Controlled Phase 2 Trial. The Lancet, 402, 529-544.
FDA. (2024). FDA's Concerns about Unapproved GLP-1 Drugs Used for Weight Loss. Safety Communication.