Retatrutide vs tirzepatide: which is better for weight loss?

Tirzepatide changed weight loss treatment when it showed patients could lose over 20% of their body weight. Now retatrutide is posting even higher numbers in trials, with some participants losing nearly 30%. Both are made by Eli Lilly. Both are once-weekly injections. The difference comes down to one extra receptor.

Here is how they stack up on mechanism, clinical data, side effects, cost, and who should consider which option.

Quick comparison

Feature	Retatrutide	Tirzepatide (Mounjaro/Zepbound)
Drug class	Triple agonist (GIP + GLP-1 + glucagon)	Dual agonist (GIP + GLP-1)
FDA approval	Not approved (Phase 3 trials)	Approved (2022 for diabetes, 2023 for obesity)
Max weight loss in trials	28.7% at 68 weeks [1]	22.5% at 72 weeks [2]
Dosing	Once weekly (2-12 mg)	Once weekly (2.5-15 mg)
Common side effects	Nausea (43%), diarrhea (33%), vomiting (21%) [1]	Nausea (33%), diarrhea (25%), vomiting (12%) [2]
Monthly cost (estimated)	Unknown (not yet available)	~$1,060/month (Zepbound list price)
Availability	Clinical trials only	Available by prescription

The key difference: two receptors vs three

Tirzepatide targets GIP and GLP-1 receptors. Retatrutide targets those same two receptors plus glucagon receptors. That third target is what makes the weight loss difference.

GLP-1 receptor activation slows gastric emptying, reduces appetite, and improves insulin sensitivity. This is the mechanism behind semaglutide (Ozempic/Wegovy) and the foundation of both drugs [3].

GIP receptor activation amplifies the insulin response and may help the body process fat more efficiently. Tirzepatide was the first drug to combine GIP with GLP-1, and the added receptor clearly improved outcomes over GLP-1 alone [4].

Glucagon receptor activation is retatrutide’s unique addition. Glucagon raises blood sugar in the short term (which sounds counterproductive), but it also increases energy expenditure and promotes fat oxidation directly in the liver [5]. This means retatrutide may burn more calories at rest and specifically target liver fat, which tirzepatide already reduces but perhaps not as aggressively.

A 2024 study in Nature Medicine found retatrutide reduced liver fat by 82.4% at 48 weeks in patients with metabolic dysfunction-associated steatotic liver disease, compared to published data showing tirzepatide reducing liver fat by approximately 50% in similar populations [6]. The difference likely comes from that glucagon component.

Weight loss data compared

Neither drug has been tested head-to-head yet. The TRIUMPH-5 trial, which directly compares retatrutide to tirzepatide, is currently underway and expected to report in 2026 [7]. Until then, we are comparing across separate trials with different populations.

Retatrutide weight loss

In the Phase 2 trial (N=338, 48 weeks), the 12 mg dose produced 24.2% mean body weight reduction [8]. The Phase 3 TRIUMPH-4 trial (N=445, 68 weeks) showed 28.7% at 12 mg and 26.4% at 9 mg in patients with obesity and knee osteoarthritis [1].

At 48 weeks, 100% of patients on 8 mg or 12 mg achieved at least 5% weight loss. At 12 mg, 26% of patients lost more than 30% of their body weight by 48 weeks [8].

Tirzepatide weight loss

In the SURMOUNT-1 trial (N=2,539, 72 weeks), the 15 mg dose produced 22.5% mean body weight reduction [2]. At the highest dose, 63% of participants lost at least 20% of body weight, and 36% lost at least 25% [2].

In patients with type 2 diabetes (SURPASS trials), tirzepatide showed 12.4% weight loss at the 15 mg dose over 40 weeks [4].

What the numbers actually tell us

Retatrutide’s numbers look better, but context matters. TRIUMPH-4 enrolled patients with higher average BMI (40.4 kg/m²) compared to SURMOUNT-1 (38.0 kg/m²). Patients with more weight to lose tend to show larger percentage reductions. The head-to-head TRIUMPH-5 data will settle this comparison properly.

Still, the magnitude of difference (28.7% vs 22.5%) is large enough that retatrutide likely does produce meaningfully more weight loss, even after adjusting for population differences.

Side effect comparison

Both drugs cause similar gastrointestinal side effects. Retatrutide appears to cause more of them, which tracks with its stronger metabolic effects.

Side effect	Retatrutide 12 mg [1]	Tirzepatide 15 mg [2]
Nausea	43.2%	33.3%
Diarrhea	33.1%	25.4%
Vomiting	20.9%	12.2%
Constipation	25.0%	11.4%
Decreased appetite	18.2%	10.5%
Dysesthesia	20.9%	Not commonly reported
Discontinuation (adverse events)	18.2%	7.1%

The dysesthesia finding in retatrutide (tingling or abnormal skin sensations in 20.9% of the 12 mg group) is notable because it does not appear at comparable rates with tirzepatide. These events were generally mild and rarely caused patients to stop treatment [1], but it is something that did not show up with dual agonists.

Discontinuation rates tell a practical story. About 18% of patients on retatrutide 12 mg stopped due to side effects vs about 7% on tirzepatide 15 mg [1][2]. The 9 mg retatrutide dose had a lower discontinuation rate of 12.2%, suggesting the side effect burden is dose-dependent.

For detailed side effect information on retatrutide, see our retatrutide side effects page.

Cost comparison

Tirzepatide pricing is established. Retatrutide pricing is speculative.

	Tirzepatide	Retatrutide (estimated)
Brand price (monthly)	~$1,060 (Zepbound)	Not yet announced
With manufacturer savings	As low as $550 with Zepbound savings card	N/A
Compounded versions	$200-$500/month	Limited availability
Insurance coverage	Growing but inconsistent	N/A

Given that Eli Lilly will be competing against its own tirzepatide product, retatrutide pricing strategy is unclear. It could be positioned as a premium option for patients who need more weight loss, or priced similarly to drive adoption. For a full breakdown of current options, see our peptide therapy cost guide.

Who should choose tirzepatide (available now)

Tirzepatide makes sense if you:

• Need a proven, FDA-approved medication today
• Have a BMI of 30+ or 27+ with a weight-related condition
• Want established safety data from large Phase 3 trials and post-market experience
• Prefer a drug with a known side effect profile and lower GI event rates
• Want insurance coverage potential

You can get started with tirzepatide through a telehealth prescription and have it shipped to your home within a week. It is the most practical choice for someone ready to start treatment now.

Who might benefit more from retatrutide (when available)

Retatrutide may be worth waiting for if you:

• Have significant weight to lose (BMI above 40) and need the strongest available tool
• Have tried tirzepatide or semaglutide with insufficient results
• Have fatty liver disease (MASLD/NASH), where retatrutide’s glucagon receptor activity may provide additional benefit
• Are willing to tolerate potentially more GI side effects for greater weight loss
• Can wait 1-2 years for FDA approval

For the latest on when retatrutide might become available, see is retatrutide FDA approved and our retatrutide access guide.

Liver fat reduction: where retatrutide pulls ahead

One area where the triple-agonist mechanism gives retatrutide a clear edge is liver fat. Metabolic dysfunction-associated steatotic liver disease (MASLD, formerly known as NAFLD) affects roughly 25-30% of adults and is closely tied to obesity.

In a Phase 2a trial published in Nature Medicine, retatrutide reduced liver fat by 82.4% at 48 weeks in patients with MASLD [6]. For context, tirzepatide reduces liver fat by approximately 50% in similar populations based on tirzepatide’s NASH trial data. Semaglutide reduces liver fat by about 40% based on published data.

The difference likely comes from glucagon receptor activation, which directly stimulates fat oxidation in the liver. This makes retatrutide potentially more useful for patients whose obesity includes significant liver involvement. Imaging studies can identify fatty liver, and your provider can check liver enzyme levels (ALT, AST) to screen for this.

The dosing experience

Both drugs follow a similar weekly injection schedule with gradual dose escalation. The titration timelines differ slightly.

Tirzepatide starts at 2.5 mg and increases by 2.5 mg every 4 weeks up to a maximum of 15 mg. Most patients reach their target dose within 16 to 20 weeks.

Retatrutide starts at 2 mg and increases every 4 weeks: 2 mg, 4 mg, 8 mg, then 12 mg. Reaching the 12 mg target dose takes about 13 weeks in the Phase 2 protocol, though Phase 3 used a slower 20 to 24 week escalation. See our retatrutide dosage chart for the full week-by-week schedule.

Both are subcutaneous injections. If you are new to self-injection, our how to inject peptides guide covers everything from needle selection to injection site rotation.

What about semaglutide?

For completeness: semaglutide vs tirzepatide is the comparison most people start with. Semaglutide (Ozempic/Wegovy) is a single GLP-1 agonist that produces about 15% weight loss at the 2.4 mg dose. It is the most widely prescribed and most affordable option, especially through compounded semaglutide. For many patients, semaglutide delivers enough weight loss to meet their goals without the higher side effect rates of dual or triple agonists.

Frequently asked questions

Is retatrutide stronger than tirzepatide?▼

Based on available clinical data, retatrutide produces more weight loss (28.7% vs 22.5% at maximum doses). But “stronger” also means more side effects. The TRIUMPH-5 head-to-head trial will provide a direct comparison using the same study population.

Can you switch from tirzepatide to retatrutide?▼

Not yet, since retatrutide is not FDA-approved. When it becomes available, switching will likely require a new titration schedule rather than a direct dose conversion. Your provider would taper off one medication and titrate up the other.

Does retatrutide work on the same receptors as tirzepatide?▼

Retatrutide activates all the same receptors as tirzepatide (GIP and GLP-1) plus glucagon receptors. Think of it as tirzepatide plus an additional metabolic lever. The glucagon component increases energy expenditure and targets liver fat.

Will retatrutide replace tirzepatide?▼

Probably not. They will likely coexist as options for different patient profiles. Tirzepatide has a better tolerability profile and will be the first-line option for many patients. Retatrutide may become the choice for patients who need more aggressive weight loss or have liver disease.

Which has fewer side effects?▼

Tirzepatide. Across trials, tirzepatide shows lower rates of nausea, diarrhea, vomiting, and treatment discontinuation compared to retatrutide. The 9 mg dose of retatrutide has a more comparable side effect profile to tirzepatide 15 mg than the 12 mg dose does.

When will we have head-to-head data?▼

The TRIUMPH-5 trial directly comparing retatrutide to tirzepatide is expected to report results in 2026 [7]. This will be the first trial that controls for population differences and provides a true apples-to-apples comparison.

Ready to start treatment with an FDA-approved option today? Find out if you qualify for tirzepatide or semaglutide through our online evaluation.

References

1. Eli Lilly. Lilly’s triple agonist, retatrutide, delivered weight loss of up to an average of 71.2 lbs along with substantial relief from osteoarthritis pain in first successful Phase 3 trial. Press release. December 11, 2025.
2. Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med. 2022;387(4):327-340.
3. Drucker DJ. Mechanisms of action and therapeutic application of glucagon-like peptide-1. Cell Metab. 2018;27(4):740-756.
4. Frías JP, Davies MJ, Rosenstock J, et al. Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes (SURPASS-2). N Engl J Med. 2021;385(6):503-515.
5. Coskun T, Urva S, Roell WC, et al. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss. Cell Metab. 2022;34(9):1234-1247.
6. Sanyal AJ, Kaplan LM, Frias JP, et al. Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial. Nat Med. 2024;30:2037-2048.
7. ClinicalTrials.gov. TRIUMPH-5: A Study of Retatrutide Compared With Tirzepatide in Participants With Obesity (NCT06108297).
8. Jastreboff AM, Kaplan LM, Frías JP, et al. Triple-hormone-receptor agonist retatrutide for obesity — a phase 2 trial. N Engl J Med. 2023;389(6):514-526.