Head to head
Retatrutide vs Tirzepatide: Cost and Trials Compared, 24% vs 22%
Published by Peptara Labs · Updated · How we research and check our pages
Retatrutide vs tirzepatide. A side-by-side comparison of the two highest-efficacy GLP-1-class peptides on the market: mechanism, clinical trial results, doses as studied, side effects, and price per vial. The 24% (Retatrutide Phase 2) and 22% (Tirzepatide Phase 3) figures come from separate trials with different durations and populations, not from a head-to-head study.
Verdict in 4 lines
- Both are top-tier GLP-1 peptides.
- Retatrutide is a newer triple-agonist with stronger Phase 2 weight-loss data (24.2%, 48 weeks).
- Tirzepatide is the FDA-approved dual-agonist with the longest real-world track record (22.5%, 72 weeks).
- Trial percentages cited below come from separate studies, not a head-to-head trial.
TL;DR comparison
One table, every row that matters. The doses row shows only what each trial tested, with its source; the recon row is vial arithmetic (a 20mg vial in 2mL bac water gives 200 units per vial and 0.1mg per unit), not a dose. See the reconstitution guide for the underlying math.
Syringe-capacity note (arithmetic, not a dose): on a standard U-100 syringe an amount above 100 units would not fit in a single draw. A more concentrated solution (1mL bac water instead of 2mL gives 0.2mg per unit) lowers the unit count. See the reconstitution guide for the concentration math.
Mechanism: triple vs dual agonist
Both peptides work by activating gut and pancreatic hormone receptors that regulate appetite, insulin secretion, and energy expenditure. The difference is how many of those receptors each one activates.
Tirzepatide (dual-agonist)
Activates two receptors: GLP-1 (glucagon-like peptide 1, slows gastric emptying and suppresses appetite) and GIP (glucose-dependent insulinotropic peptide, boosts insulin sensitivity and may modulate fat storage). The dual activation produces stronger fat loss than older single-agonist GLP-1 drugs like semaglutide.
Retatrutide (triple-agonist)
Activates all three: GLP-1, GIP, and glucagon receptor. The glucagon-receptor arm adds direct energy expenditure (the body burns more calories at rest), on top of the appetite suppression and insulin effects of GLP-1 and GIP. That third pathway is the main reason Phase 2 fat-loss numbers exceeded Tirzepatide.
Honest trade-off: more receptor activation means more potential side effects. The triple-agonist mechanism that drives Retatrutide's stronger fat-loss percentage also produced higher rates of GI events at the highest arm (12mg) in the phase 2 trial (Jastreboff et al., 2023). In the trials, the dose was raised in steps under medical supervision to limit those effects; that describes the trials, not a plan to follow.
Clinical trial results
The headline figures, the trial citations, and the disclaimer that has to come with them.
Retatrutide Phase 2
- Reference: Jastreboff et al, NEJM 2023
- Phase: 2
- n: 338
- Duration: 48 weeks
- Cohort: 12mg/wk
- Result: 24.2% mean body weight reduction
Tirzepatide Phase 3 (SURMOUNT-1)
- Reference: SURMOUNT-1, NEJM 2022
- Phase: 3
- n: 2,539
- Duration: 72 weeks
- Cohort: 15mg/wk
- Result: 22.5% mean body weight reduction
Read this before quoting either number
These percentages come from two separate clinical trials with different durations (48 vs 72 weeks), different patient populations, and different trial phases (2 vs 3). A direct percentage comparison should be read as descriptive, not causal. A head-to-head trial of Retatrutide vs Tirzepatide has not been published as of 2026. The Peptara position: cite the numbers honestly, name the trials, and never imply a direct A-beats-B finding the literature has not yet produced.
Side effects
Both share the GLP-1 class profile. Each has compound-specific notes worth flagging.
Retatrutide-specific
- Higher GI rate at 12mg vs lower doses (Phase 2)
- Triple-agonist activation can amplify early-week nausea
- Investigational compound: longer-term safety data still accumulating
Tirzepatide-specific
- FDA black-box warning: thyroid C-cell tumors (rodent data)
- Rare reports of pancreatitis
- Gallbladder events (cholelithiasis, cholecystitis)
Both trials raised the dose in steps under medical supervision, which the reports describe as part of how gastrointestinal effects were kept mostly mild to moderate (Jastreboff et al., 2022; Jastreboff et al., 2023). That describes how the trials ran, not a plan for anyone to follow. Stop and consult a licensed physician for severe or persistent GI symptoms, signs of pancreatitis, or any unusual side effect.
Doses as studied in the trials
The retatrutide phase 2 trial assigned adults to 1, 4, 8 or 12 mg once weekly (Jastreboff et al., 2023); SURMOUNT-1 assigned adults to tirzepatide 5, 10 or 15 mg once weekly (Jastreboff et al., 2022). These are the amounts the trials tested, shown for education only. They are not a schedule, and no amount here is a dose for anyone to take. Both peptides ship as a 20mg vial reconstituted with 2mL bacteriostatic water. For background on how reconstitution arithmetic works, see /reconstitution.
Retatrutide phase 2 arms
Weekly arms tested (Jastreboff et al., 2023)
- 1 mg once weekly (retatrutide phase 2 trial arm, Jastreboff et al., 2023)
- 4 mg once weekly (retatrutide phase 2 trial arm, Jastreboff et al., 2023)
- 8 mg once weekly (retatrutide phase 2 trial arm, Jastreboff et al., 2023)
- 12 mg once weekly (retatrutide phase 2 trial arm, Jastreboff et al., 2023)
Tirzepatide SURMOUNT-1 arms
Weekly arms tested (Jastreboff et al., 2022)
- 5 mg once weekly (SURMOUNT-1 trial arm, Jastreboff et al., 2022)
- 10 mg once weekly (SURMOUNT-1 trial arm, Jastreboff et al., 2022)
- 15 mg once weekly (SURMOUNT-1 trial arm, Jastreboff et al., 2022)
These are the weekly amounts each trial tested, reported for education. No amount here is a dose for anyone, and the trials do not set a dose for any individual. Tirzepatide single vials currently sold out, available in the Lumen research stack.
Price: per vial and per mg
A 20mg retatrutide vial is $174 with email signup ($205 retail), which is $8.70 per mg. A 20mg tirzepatide vial is $78 with email signup ($92 retail), $3.90 per mg; tirzepatide single vials currently sold out, available in the Lumen research stack. A monthly figure needs an amount picked for a person, so this page prices the vial and the milligram instead.
Retatrutide
$174 with email signup per 20mg vial ($205 retail)
Each phase 2 trial arm's weekly amount priced at the per-mg rate (Jastreboff et al., 2023). Price arithmetic on the trial arms, not a dose, and it does not divide a vial into weeks.
- 1 mg trial arm: $8.70 of material a week with email signup
- 4 mg trial arm: $34.80 of material a week with email signup
- 8 mg trial arm: $69.60 of material a week with email signup
- 12 mg trial arm: $104.40 of material a week with email signup
Tirzepatide
$78 with email signup per 20mg vial ($92 retail); single vials currently sold out, available in the Lumen research stack
Each SURMOUNT-1 trial arm's weekly amount priced at the per-mg rate (Jastreboff et al., 2022). Price arithmetic on the trial arms, not a dose.
- 5 mg trial arm: $19.50 of material a week with email signup
- 10 mg trial arm: $39 of material a week with email signup
- 15 mg trial arm: $58.50 of material a week with email signup
For the full per-vial and per-mg breakdown, see the retatrutide price per vial and tirzepatide price per vial. The arm figures above are arithmetic on the trials, not a dose to take.
Who should pick which
A short decision framework. No single right answer, just trade-offs that map cleanly to user profiles.
Pick Retatrutide if
- You want the highest published fat-loss percentage
- You are comfortable using an investigational compound
- You accept that phase 3 data is still being collected
- You are already familiar with the research-vial format
Pick Tirzepatide if
- You want FDA-approved status
- You prefer the longer real-world safety record
- You want the slightly lower catalog price per vial
- You want the more documented starting point
Considering both
- Tirzepatide is the FDA-approved dual-agonist; retatrutide is the investigational triple-agonist
- No trial has studied sequencing or switching between the two
- Any sequencing, switching or dose decision belongs with a licensed physician
- This site describes the trials and the prices, not a personal protocol
Frequently asked questions
Is Retatrutide better than Tirzepatide?
Retatrutide produced a higher mean body weight reduction in its Phase 2 trial (24.2% at 48 weeks, 12mg) than Tirzepatide did in SURMOUNT-1 (22.5% at 72 weeks, 15mg). But these are separate trials, not a head-to-head comparison. Different durations, different populations, different phases. Retatrutide is mechanistically a triple-agonist (GLP-1, GIP, glucagon) and tends to drive stronger fat loss in trials. Tirzepatide is dual-agonist and FDA-approved with years of real-world data. "Better" depends on whether you prioritize maximum trial percentage (Reta) or regulatory track record (Tirz).
Can I switch from Tirzepatide to Retatrutide?
That is a medical decision for a licensed physician. No published trial has studied switching between these two compounds, so this site gives no switching, washout, starting-dose or titration instructions. The two share the GLP-1 mechanism, and retatrutide adds glucagon-receptor activation that tirzepatide does not have (Jastreboff et al., 2023). Peptara does not provide medical advice.
Which has fewer side effects?
Both peptides share the GLP-1 class side-effect profile: nausea, vomiting, constipation, decreased appetite, especially in the first 2 to 4 weeks of each dose step. In the retatrutide phase 2 trial, gastrointestinal events were the most common adverse events and were dose-related (Jastreboff et al., 2023). Tirzepatide carries an FDA black-box warning for thyroid C-cell tumors (rodent data, no confirmed human signal) and has rare reports of pancreatitis and gallbladder events. Both trials raised the dose in steps under medical supervision, which the reports describe as part of how side effects were kept mostly mild to moderate; that describes the trials, not a plan for anyone to follow.
Why are these two compared so often?
They are the two highest-efficacy GLP-1-class peptides currently available in the research market. Tirzepatide is the FDA-approved benchmark for weight loss. Retatrutide is the most-anticipated next-generation candidate. Anyone optimizing for maximum fat loss in 2026 is choosing between these two, which is why "Retatrutide vs Tirzepatide" is the single highest-volume comparison query in the space.
Is Retatrutide FDA-approved?
No. As of 2026, Retatrutide is investigational. Phase 3 trials are ongoing under Eli Lilly. Tirzepatide is FDA-approved under the brand names Mounjaro (Type 2 diabetes) and Zepbound (weight loss). Peptara Labs sells Retatrutide for research use only, with full COA documentation available on request.
How much does a month of each cost at Peptara?
Priced per vial and per mg, not per month, because a monthly figure needs an amount picked for a person. A 20mg retatrutide vial is $174 with email signup ($205 retail), which is $8.70 per mg. A 20mg tirzepatide vial is $78 with email signup ($92 retail), $3.90 per mg; tirzepatide single vials currently sold out, available in the Lumen research stack. The price section shows each published trial arm priced at the per-mg rate, which is arithmetic on the trials and not a dose to take.
Are these trial numbers from the same study?
No. The 24.2% Retatrutide figure comes from Jastreboff et al, NEJM 2023, a Phase 2 trial, n=338, 48 weeks, 12mg cohort. The 22.5% Tirzepatide figure comes from SURMOUNT-1, NEJM 2022, a Phase 3 trial, n=2539, 72 weeks, 15mg cohort. These are separate trials with different durations, different patient populations, and different trial phases. A direct percentage comparison should be read as descriptive, not causal. As of 2026 no head-to-head trial of Retatrutide vs Tirzepatide has been published.
Which should a beginner choose?
This is educational information, not advice, and any choice should be made with a licensed physician. In the published record Tirzepatide is the more documented starting point for first-time GLP-1 users: it has the longer real-world track record, the FDA-approved status (the brand drugs Mounjaro and Zepbound), the wider published safety data, and a slightly lower catalog price per vial. Research-grade tirzepatide, including ours, is not an FDA-approved product. Those who already know their GLP-1 tolerance from prior cycles and want the higher fat-loss ceiling sometimes start with Retatrutide instead. Tirzepatide single vials currently sold out, available in the Lumen research stack.
Next steps
Buy Retatrutide
20mg vial, $174 with email signup, COA on request. Triple-agonist GLP-1 / GIP / glucagon.
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Buy Tirzepatide
20mg vial, $78 with email signup, COA on request, single vials currently sold out, available in the Lumen research stack. Dual-agonist GLP-1 / GIP.
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Reconstitution math
4-step method, units-not-mL formula, calculator for the catalog vials. Required reading before your first injection.
Open guide
Order either, get a research dosing reference
Order Retatrutide or Tirzepatide: third-party tested material with its batch certificate, and a written reference to the ranges published trials used.
Every order includes bac water sized to the 20mg vial, a dashboard with commonly studied ranges in units (never mL), and ongoing education support on WhatsApp. This is a reference, not a prescription. Consult a licensed physician before use.