Semaglutide vs Tirzepatide vs Retatrutide: How the GLP-1 Drugs Actually Compare

Written by NorthPeptide Research Team

For laboratory and research use only. Not for human consumption.

The GLP-1 drug space has evolved faster than any other area of metabolic pharmacology. In the span of a few years, we’ve gone from one major compound (semaglutide) to three distinct generations of metabolic peptides — each targeting more receptors than the last. But comparing them isn’t as simple as “more receptors = better.”

Let’s lay out what the data actually shows.

The Receptor Profiles

Compound	GLP-1	GIP	Glucagon	Classification
Semaglutide	Yes	No	No	Single agonist
Tirzepatide	Yes	Yes	No	Dual agonist
Retatrutide	Yes	Yes	Yes	Triple agonist

Each receptor contributes something different:

• GLP-1: Slows gastric emptying, suppresses appetite, increases insulin secretion. This is the “I’m not hungry” signal.
• GIP: Enhances insulin sensitivity, may contribute to fat metabolism. The role of GIP is still debated — it was once considered undesirable (GIP levels are elevated in obesity), but tirzepatide proved that GIP agonism paired with GLP-1 produces superior results.
• Glucagon: Increases energy expenditure, promotes hepatic fat oxidation, raises metabolic rate. This is the “burn stored energy” signal.

Weight Loss: The Numbers

All three compounds have been tested in Phase 2 or Phase 3 trials in adults with obesity. Here are the headline numbers at maximum studied doses:

Compound	Trial	Max Weight Loss	Duration	Phase
Semaglutide 2.4 mg	STEP 1	14.9%	68 weeks	Phase 3 (FDA approved)
Tirzepatide 15 mg	SURMOUNT-1	22.5%	72 weeks	Phase 3 (FDA approved)
Retatrutide 12 mg	Phase 2	24.2%	48 weeks	Phase 2 (not yet approved)

A few important caveats:

• Retatrutide’s 24.2% came from Phase 2 — smaller sample size, earlier stage. Phase 3 results could be higher or lower.
• Retatrutide’s curve hadn’t plateaued at 48 weeks — participants were still losing weight when the study ended. In a longer trial, the number could go higher.
• Trial populations differ. Baseline BMI, demographics, and inclusion criteria vary between studies, making direct cross-trial comparison imperfect.
• Placebo-subtracted numbers are more meaningful for comparison but are reported less often in headlines.

Side Effects: What Actually Happens

The GI side effect profile is similar across all three — this is a class effect of GLP-1 receptor agonism:

Side Effect	Semaglutide	Tirzepatide	Retatrutide
Nausea	~44%	~31%	~45% (high dose)
Diarrhea	~30%	~23%	~25%
Vomiting	~24%	~12%	~15%
Constipation	~24%	~12%	Not prominent

Notable differences:

• Tirzepatide appears to have a milder GI side effect profile than semaglutide at equivalent efficacy levels. This may be related to the GIP component.
• Retatrutide’s glucagon receptor activation may contribute to a small increase in resting heart rate — not seen with semaglutide or tirzepatide.
• All three are associated with gallbladder events (gallstones, cholecystitis) at rates higher than placebo — likely related to rapid weight loss rather than a direct drug effect.

Beyond Weight: Metabolic Effects

Liver Fat (NAFLD/MASH)

This is potentially the most important differentiator. While all three reduce liver fat, the magnitude differs:

• Semaglutide: Significant liver fat reduction in NAFLD trials, but MASH resolution was modest (~40% in some studies)
• Tirzepatide: SYNERGY-NASH trial showed 74% MASH resolution rate at 52 weeks with the 15 mg dose
• Retatrutide: Phase 2 data showed dramatic liver fat reduction — near-complete resolution in many participants. The glucagon receptor component likely drives enhanced hepatic fat oxidation.

Blood Sugar Control (HbA1c)

All three are effective in type 2 diabetes:

• Semaglutide: HbA1c reduction of 1.5-1.8% (SUSTAIN trials)
• Tirzepatide: HbA1c reduction of 2.0-2.4% (SURPASS trials) — consistently beat semaglutide head-to-head
• Retatrutide: Phase 2 diabetes trial showed comparable HbA1c reductions to tirzepatide

Cardiovascular

Semaglutide has the strongest cardiovascular data, with the SELECT trial demonstrating a 20% reduction in major adverse cardiovascular events. Tirzepatide’s cardiovascular outcomes trial (SURPASS-CVOT) is ongoing. Retatrutide has no cardiovascular outcomes data yet.

The Muscle Question

One of the biggest concerns with all GLP-1 class drugs is lean mass loss. When you lose 15-24% of your body weight, some of that is inevitably muscle — not just fat.

DEXA scan data suggests that 25-40% of weight lost on GLP-1 agonists is lean mass. That’s a lot. For context, dietary weight loss typically results in 20-25% lean mass loss, so these drugs appear to cause somewhat more muscle wasting than diet alone.

Retatrutide’s glucagon component is interesting here — glucagon promotes both fat oxidation and gluconeogenesis from amino acids. Whether this helps (by burning more fat) or hurts (by breaking down more protein) is an open question that Phase 3 trials will hopefully address with body composition endpoints.

Cost and Access

This section only applies to the approved drugs; retatrutide is not yet on the market:

• Semaglutide (Wegovy): ~$1,350/month list price, increasingly covered by insurance
• Tirzepatide (Zepbound): ~$1,060/month list price, more limited insurance coverage initially
• Retatrutide: Not available yet. If approved, pricing will likely be competitive with tirzepatide.

The research peptide market exists partially because of these access and cost barriers — researchers studying these compounds need affordable, high-purity material for in vitro and animal studies.

Who “Wins”?

There’s no simple answer, because the question is wrong. Each compound has a different evidence base, approval status, and research profile:

• Semaglutide wins on: longest track record, best cardiovascular data, most real-world experience, widest availability
• Tirzepatide wins on: better weight loss than semaglutide, milder side effects, strong MASH data
• Retatrutide wins on: highest weight loss numbers to date, dramatic liver fat reduction — but it’s still in Phase 2/3 and isn’t approved or available as a prescription drug

For researchers, all three represent important tools for understanding metabolic receptor pharmacology. The progression from single to dual to triple agonism is teaching us fundamental things about how these receptor systems interact — knowledge that will inform the next generation of metabolic therapeutics.

Related Research

• Retatrutide: What the Clinical Trials Actually Found
• Semaglutide Complete Research Guide
• Tirzepatide Complete Research Guide
• Cagrilintide Research Guide
• Mazdutide Research Guide

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Summary of Key Research References

Study	Year	Type	Focus	Reference
Wilding et al.	2021	Phase 3 RCT	Once-weekly semaglutide in adults with overweight or obesity (STEP 1)	PMID 33567185
Wadden et al.	2021	Phase 3 RCT	Semaglutide 2.4 mg as adjunct to intensive behavioral therapy (STEP 3)	PMC7905697
Frias et al.	2021	Phase 3 RCT	Tirzepatide vs semaglutide in type 2 diabetes (SURPASS-2)	PMID 34170647
Jastreboff et al.	2023	Phase 2 RCT	Triple-hormone-receptor agonist retatrutide for obesity	PMID 37366315
Romero-Gomez et al.	2024	Phase 2a RCT	Retatrutide for metabolic dysfunction-associated steatotic liver disease	PMC11271400
Tan et al.	2022	Review	Once-weekly semaglutide for weight management: a clinical review	PMC9272494
Mahapatra et al.	2023	Review	Efficacy and safety of tirzepatide in type 2 diabetes and obesity management	PMC10088547
Karagiannis et al.	2024	Review	GLP-1 single, dual, and triple receptor agonists for type 2 diabetes and obesity	PMC11402415

NorthPeptide does not sell semaglutide, tirzepatide, or retatrutide. This article is for informational and educational purposes only. All products are for laboratory and research use. Not for human consumption.