Retatrutide: The Triple-Hormone GLP-1 That May Beat Semaglutide & Tirzepatide
Retatrutide targets GLP-1, GIP, and glucagon. Learn about this next-gen weight loss medication.
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The next frontier in GLP-1 treatment
Just as tirzepatide improved on semaglutide by targeting two hormone receptors instead of one, retatrutide takes the next leap: targeting three. This investigational medication from Eli Lilly activates GLP-1, GIP, and glucagon receptors simultaneously, and early results suggest it may produce the greatest weight loss of any GLP-1 medication — up to 24.2% in Phase 2 trials.
While not yet FDA-approved, retatrutide represents the future of metabolic medicine. Here is everything we know so far.
How retatrutide works: the triple agonist advantage
| Hormone Receptor | What It Does | Effect on Weight Loss | Other Benefits |
|---|---|---|---|
| GLP-1 receptor | Reduces appetite, slows gastric emptying | Appetite suppression, reduced food intake | Improves glucose, cardiovascular protection |
| GIP receptor | Enhances insulin secretion, improves fat metabolism | Improved fat utilization, reduced fat storage | Better glucose control, reduced inflammation |
| Glucagon receptor | Increases energy expenditure, promotes fat burning | More calories burned, enhanced fat loss | Liver fat reduction, improved lipid profile |
| Triple combination | All three mechanisms simultaneously | Maximum weight loss potential | Comprehensive metabolic improvement |
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Retatrutide vs semaglutide vs tirzepatide
| Feature | Semaglutide (Wegovy) | Tirzepatide (Zepbound) | Retatrutide (investigational) |
|---|---|---|---|
| Hormone targets | GLP-1 only | GLP-1 + GIP | GLP-1 + GIP + Glucagon |
| Average weight loss | ~15% | ~20 to 22.5% | ~24.2% (Phase 2 data) |
| Administration | Weekly injection | Weekly injection | Weekly injection (expected) |
| FDA approval | Approved (obesity, CV) | Approved (obesity, OSA) | Not yet approved |
| Cardiovascular benefits | SELECT trial: 20% CV reduction | SURPASS: significant | Expected (trials ongoing) |
| Side effects | GI (nausea, vomiting, diarrhea) | GI (similar to semaglutide) | GI (similar, plus glucagon effects) |
| Expected availability | Available now | Available now | 2026 to 2027 (estimated) |
Phase 2 trial results: the TRIUMPH data
| Dose | Weight Loss at 24 weeks | Weight Loss at 48 weeks | % Achieving 15%+ Loss | % Achieving 20%+ Loss |
|---|---|---|---|---|
| 1 mg | ~7% | ~9% | ~20% | ~5% |
| 4 mg | ~12% | ~17% | ~55% | ~30% |
| 8 mg | ~17% | ~22% | ~75% | ~55% |
| 12 mg | ~18% | ~24.2% | ~85% | ~70% |
| Placebo | ~2% | ~2.5% | ~0% | ~0% |
The glucagon advantage: why three is better than two
| Benefit | Mechanism | Unique to Retatrutide? | Impact |
|---|---|---|---|
| Increased energy expenditure | Glucagon receptor activation increases metabolic rate | Yes — not in semaglutide or tirzepatide | More calories burned at rest |
| Enhanced fat oxidation | Glucagon promotes fat burning over storage | Yes | Greater fat loss, less muscle loss |
| Liver fat reduction | Glucagon directly reduces liver fat production | Enhanced vs other GLP-1s | Significant for fatty liver disease |
| Improved lipid profile | Glucagon reduces VLDL and triglycerides | Enhanced | Better cholesterol improvement |
| Thermogenic effect | Glucagon increases body heat production | Yes | Additional calorie burning |
Side effect profile of retatrutide
| Side Effect | Frequency | Severity | Comparison to Other GLP-1s |
|---|---|---|---|
| Nausea | 30 to 50% | Mild to moderate | Similar to tirzepatide |
| Diarrhea | 15 to 30% | Mild to moderate | Similar |
| Vomiting | 10 to 20% | Mild to moderate | Similar |
| Constipation | 10 to 20% | Mild | Similar |
| Injection site reactions | 5 to 10% | Mild | Similar |
| Increased heart rate | Variable | Mild (2 to 6 bpm) | Slightly more than semaglutide |
| Skin-related (glucagon effect) | Being monitored | Mild | Unique — under investigation |
Development timeline and expected approval
| Phase | Status | Timeline | Key Milestone |
|---|---|---|---|
| Phase 1 | Completed | 2020 to 2021 | Safety and dosing established |
| Phase 2 | Completed | 2022 to 2024 | 24.2% weight loss demonstrated |
| Phase 3 (TRIUMPH) | Ongoing | 2024 to 2026 | Confirming efficacy and safety in larger population |
| FDA filing | Expected | 2025 to 2026 | New Drug Application submission |
| FDA review | Expected | 6 to 12 months after filing | FDA evaluates safety and efficacy |
| Approval (if successful) | Expected | Late 2026 to 2027 | Available by prescription |
Frequently asked questions
What is retatrutide?
Retatrutide is an investigational triple-hormone receptor agonist that targets GLP-1, GIP, and glucagon receptors simultaneously. Developed by Eli Lilly, it is being studied for obesity and type 2 diabetes. Early trial results show weight loss of up to 24% — potentially exceeding both semaglutide (15%) and tirzepatide (22.5%). It is not yet FDA-approved but is expected to file for approval in 2025 to 2026.
How does retatrutide compare to semaglutide and tirzepatide?
Retatrutide targets three hormone receptors (GLP-1, GIP, glucagon) while semaglutide targets only GLP-1 and tirzepatide targets GLP-1 and GIP. The addition of glucagon receptor agonism is expected to increase energy expenditure and fat burning, potentially producing greater weight loss. Phase 2 results showed up to 24% weight loss at 48 weeks, compared to 15% for semaglutide and 22.5% for tirzepatide.
When will retatrutide be available?
Retatrutide is currently in Phase 3 clinical trials (TRIUMPH program). If trials complete successfully, Eli Lilly is expected to file for FDA approval in 2025 to 2026. If approved, retatrutide could be available by late 2026 or 2027. The exact timeline depends on trial results and FDA review process.
What are the side effects of retatrutide?
Side effects are similar to other GLP-1 medications: nausea, vomiting, diarrhea, constipation, and injection site reactions. The glucagon receptor component may cause additional effects related to increased energy expenditure. Phase 2 data shows the side effect profile is comparable to tirzepatide, with most adverse events being mild to moderate GI symptoms.
How much weight can you lose on retatrutide?
Phase 2 trial results showed weight loss of up to 24.2% at 48 weeks at the highest dose (12 mg). This is the highest weight loss reported for any GLP-1 medication in clinical trials. Phase 3 trials are confirming these results. If approved, retatrutide could become the most effective weight loss medication available.
Why does retatrutide target three hormones?
Each hormone target serves a purpose: GLP-1 reduces appetite and improves glucose, GIP enhances insulin secretion and fat metabolism, and glucagon increases energy expenditure and fat burning. The triple combination is designed to produce greater weight loss than targeting one or two receptors alone. The glucagon component specifically may help burn more calories.
Will retatrutide replace semaglutide and tirzepatide?
Not necessarily replace, but it may become the preferred option for people needing maximum weight loss. Semaglutide and tirzepatide will likely remain important options, especially for patients who respond well to them or have specific conditions like cardiovascular disease (semaglutide) or sleep apnea (tirzepatide). Retatrutide will add another option, not replace existing treatments.
Should I wait for retatrutide or start semaglutide/tirzepatide now?
Do not wait. If you qualify for GLP-1 treatment now, starting semaglutide or tirzepatide can deliver significant health benefits immediately. Retatrutide may not be available until 2026 to 2027, and waiting means losing valuable time for weight loss and health improvement. You can always switch to retatrutide later if it becomes available and offers advantages for your situation.
Conclusion
Retatrutide represents the exciting future of GLP-1 treatment. By targeting three hormone receptors instead of one or two, it may achieve the greatest weight loss of any medication in this class — up to 24.2% in Phase 2 trials. The addition of glucagon receptor agonism provides a unique fat-burning mechanism not found in current GLP-1s. While we await Phase 3 results and FDA approval (expected 2026 to 2027), the current options — semaglutide and tirzepatide — remain highly effective and available now. If you are considering GLP-1 treatment, do not wait for retatrutide. Start your journey now and switch later if retatrutide proves to be a better option for you.
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