Retatrutide vs tirzepatide: which is better for weight loss?

Retatrutide hit 24.2% body weight reduction in 48 weeks during its phase 2 trial [1]. Tirzepatide, already FDA-approved and widely prescribed, reached 22.5% at 72 weeks in SURMOUNT-1 [2]. Those numbers make retatrutide look like the clear winner, but the comparison is more complicated than a single percentage. The trials used different durations, different patient populations, and different dosing schedules. And one of these drugs you can actually get right now.

If you’re weighing your options for GLP-1-based weight loss therapy, here’s how the two compare on the metrics that matter.

Quick comparison table

Feature	Retatrutide	Tirzepatide
Drug class	Triple agonist (GIP + GLP-1 + glucagon)	Dual agonist (GIP + GLP-1)
Mechanism	Activates three receptors for appetite, metabolism, and fat burning	Activates two receptors for appetite and insulin
FDA approval	Not approved (phase 3 trials ongoing)	Approved as Mounjaro (T2D) and Zepbound (obesity)
Best trial weight loss	24.2% at 48 weeks (phase 2, 12mg) [1]	22.5% at 72 weeks (SURMOUNT-1, 15mg) [2]
Dosing	Once weekly subcutaneous injection	Once weekly subcutaneous injection
Common side effects	Nausea (up to 45%), diarrhea (33%), vomiting (23%) [1]	Nausea (24-31%), diarrhea (17-23%), vomiting (9-12%) [2]
Monthly cost (brand)	Not yet available (estimated $1,000-1,500 post-approval)	~$1,000-1,100/month without insurance
Monthly cost (compounded)	$200-600/month (research/compounded)	$99-399/month
Availability	Research use and select telehealth clinics only	Widely available by prescription

The key difference: two receptors vs three

Both drugs are made by Eli Lilly. Both target GIP and GLP-1 receptors to suppress appetite and improve blood sugar control. But retatrutide adds a third target: the glucagon receptor.

That glucagon component is what makes retatrutide genuinely different, not just a slightly tweaked version of tirzepatide. Glucagon receptor activation increases energy expenditure and promotes fat oxidation directly. Your body burns more calories and preferentially targets fat stores for fuel [3]. This may explain why retatrutide produced faster weight loss in a shorter trial window.

Tirzepatide works through GIP and GLP-1 receptors to slow gastric emptying, reduce appetite, and improve insulin sensitivity. It’s proven, well-studied across multiple phase 3 trials, and has years of real-world prescribing data behind it [2]. If you want to understand the full picture of how these receptor pathways work, our guide to how peptides work breaks it down.

How retatrutide works

Retatrutide (LY3437943) is a single molecule that activates three hormone receptors simultaneously. Eli Lilly designed it specifically to outperform dual-agonist drugs by adding glucagon receptor activity on top of the GIP and GLP-1 pathways.

In the phase 2 trial published in the New England Journal of Medicine, 338 adults with obesity received retatrutide at doses ranging from 1mg to 12mg weekly for 48 weeks [1]. The results at the highest dose (12mg) were striking:

• 24.2% mean body weight reduction
• 100% of participants lost at least 5% of their body weight
• 93% lost at least 10%
• 83% lost at least 15%

For context, those response rates are higher than anything published for tirzepatide or semaglutide in their respective trials. And the weight loss curves hadn’t fully plateaued at 48 weeks, suggesting the final numbers could be even higher in longer studies [1].

Retatrutide also showed a striking effect on liver fat. In a separate phase 2a trial, it reduced liver fat by up to 82% in patients with metabolic dysfunction-associated steatotic liver disease (MASLD) [4]. No other GLP-1 class drug has shown that level of liver fat reduction.

For a deeper look at the drug’s mechanism, dosing, and trial history, see our full retatrutide guide.

How tirzepatide works

Tirzepatide targets GIP and GLP-1 receptors. It was the first dual-agonist to receive FDA approval, first as Mounjaro for type 2 diabetes in May 2022, then as Zepbound for chronic weight management in November 2023.

The landmark SURMOUNT-1 trial enrolled 2,539 adults with obesity (BMI of 30 or higher, or 27+ with a weight-related condition) and ran for 72 weeks [2]. The results by dose:

• 5mg: 15.0% mean weight loss
• 10mg: 19.5% mean weight loss
• 15mg: 20.9% mean weight loss (22.5% in the efficacy estimand)

Over a third of participants on the 15mg dose lost more than 25% of their body weight [2]. Those numbers made tirzepatide the most effective FDA-approved weight loss medication at the time of approval.

Tirzepatide also has strong data for type 2 diabetes from the SURPASS trial series and additional obesity data from SURMOUNT-2, SURMOUNT-3, and SURMOUNT-4. That depth of evidence across thousands of patients is something retatrutide can’t match yet.

If you’re considering a tirzepatide prescription, our tirzepatide online prescription guide covers the process.

Side effects comparison

Both drugs cause GI side effects. That’s expected with any drug that activates GLP-1 receptors. But retatrutide’s side effect rates run higher, likely because the glucagon receptor adds its own GI impact on top of the dual-agonist effects.

Retatrutide (phase 2, 12mg dose) [1]:

• Nausea: up to 45%
• Diarrhea: 33%
• Vomiting: 23%
• Constipation: 16%
• Dose-dependent heart rate increase (peaked at week 24, declined after)

Tirzepatide (SURMOUNT-1, 15mg dose) [2]:

• Nausea: 24-31%
• Diarrhea: 17-23%
• Vomiting: 9-12%
• Constipation: 11-13%

In both cases, GI side effects were concentrated during the dose-escalation period and faded with continued use. Starting at a lower dose and escalating gradually helped reduce severity [1][2]. Most side effects were mild to moderate, and discontinuation rates due to adverse events stayed under 7% in both trials.

One side effect unique to retatrutide: altered skin sensation. Some participants reported tingling or unusual skin sensitivity. These were mild, didn’t cause anyone to drop out, and didn’t correlate with the amount of weight lost [1].

For more on what to expect with retatrutide specifically, see our retatrutide side effects page.

Cost comparison

This is where the practical gap is widest right now.

Tirzepatide (available now):

• Brand-name Mounjaro/Zepbound: ~$1,000-1,100/month without insurance
• With commercial insurance: copays vary, often $25-150/month with manufacturer savings cards
• Compounded tirzepatide: $99-399/month through telehealth clinics [5]

Retatrutide (not yet FDA-approved):

• Research-grade peptide: $150-500/month (quality varies widely)
• Compounded versions through select clinics: $200-600/month
• Projected brand-name price post-approval: $1,000-1,500/month [6]

Compounded tirzepatide is the most affordable proven option right now. Brand-name Zepbound carries a higher price tag but offers the security of FDA-regulated manufacturing and insurance coverage for qualifying patients.

Retatrutide from research or compounded sources carries more risk. Without FDA approval, there’s no standardized manufacturing process, and you have limited recourse if something goes wrong. The difference between compounded and research peptides matters here.

Want to see if you qualify for prescribed weight loss medication at lower cost? Check your eligibility at glp.purepeptideclinic.com.

Who should choose what

Tirzepatide makes sense if you:

• Want a drug with FDA approval and years of safety data
• Need insurance coverage to afford treatment
• Prefer the peace of mind that comes with an established medication
• Have type 2 diabetes (Mounjaro is specifically approved for this)

Retatrutide might be worth watching if you:

• Haven’t responded well to GLP-1-only or dual-agonist drugs
• Are interested in the added metabolic benefits of glucagon receptor activation
• Have fatty liver disease (the MASLD data is particularly promising)
• Are comfortable waiting for phase 3 results and FDA review

The honest answer: for most people right now, tirzepatide is the better choice. It’s available, it’s proven, and you can get it through legitimate medical channels with a prescription. Retatrutide’s early numbers are exciting, but phase 2 trials are small. The TRIUMPH phase 3 program is ongoing, with primary obesity results expected in 2026 and a realistic FDA approval window of 2027-2028 [7].

The two drugs aren’t direct competitors yet. They will be, eventually. When retatrutide has full phase 3 data and FDA approval, the comparison will be much clearer.

A note on comparing trial results

It’s tempting to line up 24.2% vs 22.5% and declare retatrutide the winner. But these numbers come from different trials with different designs:

• Retatrutide phase 2: 338 participants, 48 weeks, dose range 1-12mg [1]
• Tirzepatide SURMOUNT-1: 2,539 participants, 72 weeks, dose range 5-15mg [2]

The retatrutide trial was shorter, smaller, and the weight loss curve hadn’t plateaued. Tirzepatide’s trial was longer and larger, giving a more reliable picture of real-world outcomes. Head-to-head trials comparing the two drugs at equivalent time points don’t exist yet. Until they do, any direct comparison should be taken with that context.

FAQ

Is retatrutide FDA approved?▼

No. Retatrutide is currently in phase 3 clinical trials under Eli Lilly’s TRIUMPH program. The earliest realistic FDA approval date is 2027-2028, depending on when the primary trials report results and how quickly the FDA reviews the application [7].

Can I get retatrutide prescribed right now?▼

Not through standard FDA-approved channels. Some telehealth clinics and compounding pharmacies offer retatrutide, but these are not FDA-approved formulations. If you’re interested in a proven weight loss medication you can get today, tirzepatide and semaglutide are both available by prescription.

Is retatrutide stronger than tirzepatide?▼

Phase 2 data suggests retatrutide may produce greater weight loss in a shorter timeframe, likely due to its additional glucagon receptor activity [1]. But “stronger” isn’t the full story. The phase 2 trial was small, and we need phase 3 data to know if those results hold in larger, more diverse populations. Tirzepatide’s data is far stronger at this point.

What is a triple agonist?▼

A triple agonist activates three different hormone receptors with a single molecule. Retatrutide targets GIP, GLP-1, and glucagon receptors simultaneously. For comparison, tirzepatide is a dual agonist (GIP + GLP-1), and semaglutide is a single agonist (GLP-1 only) [3].

Are the side effects of retatrutide worse than tirzepatide?▼

Phase 2 data shows higher rates of nausea, diarrhea, and vomiting with retatrutide compared to tirzepatide’s published trial data [1][2]. The glucagon receptor component likely contributes to this. Slower dose escalation (starting at 2mg rather than 4mg) reduced side effect severity in the trial. Phase 3 data with optimized dosing schedules may improve the side effect profile.

Which drug is cheaper?▼

Right now, compounded tirzepatide ($99-399/month) is the most affordable option with clinical backing. Retatrutide through compounding runs $200-600/month, but without FDA approval, quality and safety aren’t standardized [5][6]. Brand-name tirzepatide (Mounjaro/Zepbound) costs around $1,000-1,100/month without insurance.

Will retatrutide replace tirzepatide?▼

Probably not. Even if retatrutide proves more effective, tirzepatide has massive commercial infrastructure, insurance contracts, and years of safety data. More likely, they’ll coexist as options for different patient profiles, similar to how semaglutide and tirzepatide both have their place today.

Should I wait for retatrutide or start tirzepatide now?▼

If you qualify for weight loss medication today and your weight is affecting your health, waiting 2-3 years for a drug that might be marginally better doesn’t make medical sense. Start with what’s available and proven. You can always switch later if retatrutide earns its approval and shows clear advantages in phase 3 data.

Find out which GLP-1 medication is right for you at glp.purepeptideclinic.com.

References

1. 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. doi:10.1056/NEJMoa2301972

2. Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(3):205-216. doi:10.1056/NEJMoa2206038

3. 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: from discovery to clinical proof of concept. Cell Metab. 2022;34(9):1234-1247.

4. 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(7):2037-2048. doi:10.1038/s41591-024-03018-2

5. Eli Lilly and Company. Lilly’s SURMOUNT-1 results published in The New England Journal of Medicine. Press release. May 13, 2022.

6. GLP3 Planner. Retatrutide cost in 2026. Published February 2026. Accessed April 2026.

7. PeptideDeck. Is retatrutide FDA approved? Approval date, trial timeline and what to expect. Published April 2026. Accessed April 2026.