Weight loss
The world's first triple-action weight loss peptide that simultaneously activates three hormone receptors—GIP, GLP-1, and glucagon—delivering unprecedented weight loss results of up to 24% body weight in clinical trials.
Start here
Retatrutide is an injectable weight-loss peptide that activates three hormone receptors at once — GLP-1 (a gut hormone that tells your brain you're full), GIP, and glucagon — the first compound of its kind 12. In clinical trials, people lost up to 24% of their body weight on average at higher doses over 48 weeks 1. It is still in Phase 1-2 human trials and is a research compound, not an approved medicine.
Think of retatrutide as a master key that unlocks three different locks in your body's weight regulation system. First, it activates GLP-1 (a gut hormone that tells your brain you're full) receptors in your brain to reduce hunger and help you feel full faster. Second, it hits GIP receptors which help your body handle nutrients better and may improve how fat cells work. Third—and this is what makes retatrutide special—it activates glucagon receptors, which tells your body to burn more fat for energy 2. It's like having three different weight-loss helpers working together at once, which is why the results are so dramatic.
Retatrutide (LY3437943) is a single molecule that switches on three receptors at once, in a balanced way (a triagonist): the receptors for glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1 (a gut hormone that tells your brain you're full)), and glucagon (GCG) 2. These are three hormones that control appetite, blood sugar and energy use. Switching on the GLP-1 receptor lowers appetite through signals in the hypothalamus (the brain's hunger-control area), slows stomach emptying, and boosts insulin release when blood sugar is high. Switching on the GIP receptor adds to the insulin release triggered by gut hormones (the incretin effect) and may help fat tissue work better. The glucagon receptor part is what sets retatrutide apart. It increases sugar production by the liver and the breakdown of fat (lipolysis (fat breakdown)), raises fatty acid burning, and increases energy use by making heat (thermogenesis) 2. A C20 fatty diacid (a fatty acid chain) attached to lysine-17 (one amino acid in the chain) lets the drug attach to albumin (a protein that carries things in the blood). This extends its half-life (the time for half the drug to clear) to approximately 6 days, so one shot a week is enough. Compared with the body's own hormones, retatrutide is approximately 0.3x as potent at the glucagon receptor and 0.4x at the GLP-1 receptor, but roughly 8.9x more potent at the GIP receptor. This mix gives it a distinct profile that aims to maximize metabolic benefits while managing side effects.
Evidence check
Some human studies
It has been tested in people, but only in small or early-stage studies. Promising, but not yet proven the way an approved medicine is.
Every numbered marker on this page links to one of the 14 sources at the bottom.
Weight Loss Power
Delivers the highest weight loss ever recorded in Phase 2 obesity trials—up to 24% body weight reduction at the 12mg dose
Metabolic Health
Dramatically improves blood sugar, HbA1c, and metabolic markers through triple receptor activation
Appetite Control
Powerfully reduces hunger and cravings through multiple brain pathways, making dietary changes feel natural
The most-asked question
Retatrutide is dose-escalated: the studies start everyone low and step the dose up on a schedule, so the right amount depends on the week you're on. The research-reported maintenance range is 4–8 mg, once weekly.
Weeks 1-4 (then raise the dose by 2 mg every 4 weeks)
2 mg
Phase 2 obesity trial initiated higher-dose arms at 2 mg weekly with stepwise 2 mg increases every 4 weeks to limit GI effects 1.
Ongoing, after the slow step-up in dose
4-8 mg
Mid-range maintenance doses; 8 mg produced ~22% mean weight loss at 48 weeks in the phase 2 trial 13.
Ongoing (highest dose studied)
12 mg
Highest studied dose; produced ~24% mean weight reduction at 48 weeks 1. Still investigational (not FDA-approved).
The ceiling: 12 mg once weekly (highest dose studied in Phase 2 trials)
Reconstitution, in plain words
Peptides usually arrive as a freeze-dried powder in a small vial. “Reconstitution” just means adding sterile water back in so you can measure a dose. Here's how it works for Retatrutide:
Most clinical trials used pre-filled delivery systems. If using research vials, typical concentration allows direct withdrawal of the prescribed dose. Example: 5mg/mL concentration—for a 4mg dose, draw 0.8mL.
For research purposes with a 5mg/mL solution: 1mg dose = 0.2mL (20 units on insulin syringe), 4mg dose = 0.8mL (80 units), 8mg dose = 1.6mL (may require two injections), 12mg dose = 2.4mL (multiple injection sites needed).
Three quick questions — your vial, your water, your dose — and it tells you the exact syringe mark. “Find dose amount” is preloaded with Retatrutide's recorded schedule.
Injection sites & technique
Injection under the skin—the same easy technique used for insulin
Timing
Pick any consistent day each week—what matters most is doing it the same day each week. Many people choose weekend mornings so any initial nausea happens when they can rest.
Inject regardless of food timing. However, eating slowly and avoiding large, fatty meals helps minimize nausea. Many users find eating smaller, more frequent meals works better on this medication.
Do not combine with other GLP-1 (a gut hormone that tells your brain you're full) drugs like semaglutide or tirzepatide, because retatrutide already hits all three of its targets (GLP-1, GIP, and glucagon receptors) 2. Metformin (a common diabetes drug) is safe and often useful to continue 6.
The honest list
These show up most often. They usually fade as your body adjusts.
The most frequently reported side effect, especially during dose escalation 3. Your gut has lots of GLP-1 (a gut hormone that tells your brain you're full) receptors, and they need time to adjust.
What to do Start with lower doses and increase gradually. Eat smaller meals, avoid fatty foods, and stay hydrated. Usually improves significantly after the first few weeks.
Common in the first weeks of treatment as your digestive system adapts to the medication's effects on gut motility.
What to do Stay well hydrated. Avoid greasy, spicy, or high-fiber foods initially. Usually resolves within 2-4 weeks as your body adjusts.
Some users experience the opposite—slowed digestion can lead to constipation, especially at higher doses.
What to do Increase water intake significantly. Add fiber gradually. Gentle physical activity helps. Over-the-counter remedies are safe if needed.
This is actually the intended effect! But it can feel strange at first when you realize you're simply not hungry.
What to do This is generally positive but ensure you're still eating nutritious foods. Don't skip meals entirely—aim for smaller, protein-rich meals.
Worth knowing about, but most people never see these.
Some users notice their resting heart rate increases by 5-10 beats per minute 1. This appeared to peak at 24 weeks and decrease afterward in trials 1.
What to do Monitor your heart rate. This effect is usually mild and not dangerous for most people. Report persistent or significant increases to your healthcare provider.
Redness, itching, or mild swelling at the injection site. Usually minor and temporary.
What to do Rotate injection sites regularly. Ensure proper injection technique. Clean the area before injecting. Reactions typically resolve within a few days.
Rare, but if any of these happen, stop and contact a medical professional.
Inflammation of the pancreas is a known risk with all GLP-1 (a gut hormone that tells your brain you're full) class medications 8. Symptoms include severe, persistent abdominal pain that may radiate to the back.
What to do STOP the medication immediately and seek emergency medical care if you experience severe abdominal pain. This is rare but serious.
Rapid weight loss can increase risk of gallstones 9. Symptoms include pain in the upper right abdomen, nausea, and vomiting.
What to do Report any right-sided abdominal pain to your healthcare provider. May require imaging and in some cases gallbladder removal.
Week by week
Is it right for you?
Retatrutide is an investigational medication currently in clinical trials. It is not FDA approved. Any use should be under the supervision of a qualified healthcare provider. Never start, stop, or change your dose without medical guidance.
High interaction risk. Retatrutide dramatically lowers blood sugar—insulin doses typically need significant reduction (20-50%) to prevent hypoglycemia (dangerously low blood sugar).
Higher risk of hypoglycemia (dangerously low blood sugar). These drugs also make the body release insulin. A lower dose is usually needed.
Safe and often beneficial combination. Metformin works through different mechanisms and complements retatrutide well.
Generally safe combination used in clinical trials. Both promote weight loss through different mechanisms.
Food and pills move more slowly through your gut, which may affect absorption. Consider using backup contraception or switch to non-oral methods.
Take thyroid medication at least 30-60 minutes before retatrutide or 4 hours after. Slower movement through the gut may affect absorption.
Do NOT combine. Both act on the GLP-1 (a gut hormone that tells your brain you're full) receptor (a docking site for a gut hormone that lowers appetite). Using them together provides no additional benefit and increases side effects.
Do NOT combine. Retatrutide already acts on both the GIP and GLP-1 (a gut hormone that tells your brain you're full) receptors (docking sites for two gut hormones) that tirzepatide targets, plus the glucagon receptor.
Limited interaction data. Theoretically safe as they work through different mechanisms, but use caution.
No direct interaction known. Some users stack for body composition, but data is limited.
Drugs like this one (GLP-1 (a gut hormone that tells your brain you're full) agonists (compounds that switch a receptor on)) may reduce B12 absorption over time. Consider supplementation, especially long-term.
Safe and often helpful to maintain adequate protein intake while eating less overall.
Safe but start slowly. Can help with constipation but may worsen early stomach and gut symptoms if added too quickly.
Safe and recommended. When eating less food, making sure you get enough vitamins and minerals is important.
If you need to lose a substantial amount of weight, retatrutide is showing unprecedented results. Phase 2 trials demonstrated average weight loss of 24% at the highest dose—that's nearly 60 pounds for someone weighing 250 lbs 1. No other medication has matched this 1.
Retatrutide tackles both problems at once. It greatly improves blood sugar control (HbA1c, your 3-month average blood sugar, drops by up to 2%) while delivering major weight loss 6. That dual benefit makes it especially valuable for people with diabetes who struggle with weight.
If you're dealing with the cluster of issues that includes high blood sugar, excess belly fat, abnormal cholesterol, and high blood pressure, retatrutide's triple mechanism attacks multiple aspects of metabolic dysfunction simultaneously 5.
Early research shows retatrutide may significantly reduce liver fat 7. For people with non-alcoholic fatty liver disease, this peptide offers hope through weight loss plus direct metabolic improvements that benefit liver health.
Retatrutide has shown a generally favorable safety profile in Phase 1 and Phase 2 clinical trials involving over 600 participants 16. Most side effects are gastrointestinal and tend to improve over time 3. The medication appears well-tolerated when doses are increased gradually. No major safety signals have emerged, but larger Phase 3 trials are still ongoing 3.
Current safety data comes from Phase 1 and Phase 2 trials conducted by Eli Lilly. Multiple Phase 3 trials are currently underway to establish long-term safety in larger populations. As a research compound not yet FDA approved, the full safety profile is still being established.
Keeping it good
Keep retatrutide refrigerated at 36-46°F (2-8°C). Protect from light by keeping in original packaging. Never freeze the medication. Can tolerate brief periods at room temperature (up to 86°F/30°C) for transport.
Once prepared for use, store refrigerated at 36-46°F (2-8°C). Do not freeze reconstituted solution. Keep away from direct light. Use within 28 days of first use.
Not our opinion — the published record
2023
In 338 adults with obesity, retatrutide produced dose-dependent weight loss (more drug, more weight lost) of up to 24.2% at 48 weeks with the 12mg dose. That is the highest ever recorded for any anti-obesity medication in a Phase 2 trial (a mid-stage study). Even the lowest dose (1mg) outperformed placebo.
Jastreboff AM, Kaplan LM, Frías JP et al.
2024
This comprehensive review confirmed that retatrutide's unique mechanism of acting on three receptors offers advantages over single or dual agonists (drugs that act on one or two receptors). Switching on the glucagon receptor may add extra energy use and fat burning not seen with GLP-1-only drugs.
Kaur M, Misra S
2025
Pooled analysis of all available trials confirmed that retatrutide shows a clear dose-response relationship for weight loss (higher doses, more weight lost). Serious side effects were comparable to placebo, with stomach and gut (GI) symptoms being the main tolerability concern.
Tewari J, Qidwai KA, Tewari A et al.
2025
In a DXA substudy (a side study using body scans that measure fat and muscle) of adults with type 2 diabetes, total fat mass fell 15.2% (4 mg), 26.1% (8 mg) and 23.2% (12 mg) at 36 weeks versus 4.5% with placebo and 2.6% with dulaglutide. The proportion of lean mass (muscle and other non-fat tissue) lost relative to total weight lost was similar to other obesity treatments. A greater share of lean mass was not lost despite the larger weight loss.
Coskun T, Wu Q, Schloot NC et al.
2025
This review compared retatrutide with other obesity medicines. It noted that acting on three receptors is a new frontier in drug treatment for metabolic disease (problems with weight, blood sugar and energy use), with potential to address several aspects of metabolic disease at once.
Goldney J, Hamza M, Surti F
2023
In 281 adults with type 2 diabetes treated with diet and exercise alone or a stable dose of metformin, retatrutide reduced HbA1c (a blood test that shows average blood sugar) by up to 2.02% at 24 weeks and body weight by up to 16.94% at 36 weeks. Mild-to-moderate stomach and gut (GI) side effects occurred in 35% of retatrutide-treated participants, with no reports of severe hypoglycemia (dangerously low blood sugar).
Rosenstock J, Frias J, Jastreboff AM et al.
2024
In a 98-participant substudy of adults with MASLD (fatty liver disease linked to weight and blood sugar problems) and at least 10% liver fat, retatrutide reduced liver fat by 81.4% (8 mg) and 82.4% (12 mg) relative to baseline at 24 weeks versus a 0.3% increase with placebo. Most participants on the two highest doses reached normal liver fat (under 5%) by 24 weeks.
Sanyal AJ, Kaplan LM, Frias JP et al.
2023
In a cohort study (a study that follows groups of people over time) of patients using GLP-1 receptor agonists (liraglutide or semaglutide) for weight loss, GLP-1 agonist use was linked to a higher risk of pancreatitis (inflamed pancreas) (adjusted hazard ratio 9.1; a ratio above 1 means higher risk), bowel obstruction (4.2), and gastroparesis (slow stomach emptying) (3.7) compared with bupropion-naltrexone users.
Sodhi M, Rezaeianzadeh R, Kezouh A et al.
1989
Among 51 obese subjects on an 8-week very-low-calorie diet, 25.5% developed gallstones on ultrasound versus none in the non-dieting comparison group, and three required gallbladder removal—establishing rapid weight loss as a risk factor for gallstone formation.
Liddle RA, Goldstein RB, Saxton J
If this isn't the right fit
Your questions
Tirzepatide is a dual agonist (it switches on two hormone targets): GIP and GLP-1 (a gut hormone that tells your brain you're full). Retatrutide adds a third target, the glucagon receptor, which appears to increase fat burning and energy use beyond what two targets achieve 2. This triple action may explain why retatrutide produced more weight loss (24%) than tirzepatide (21%) in their respective trials 110.
Retatrutide is currently in Phase 3 clinical trials 11. If trials are successful and FDA approves it, the earliest it could potentially be available is 2026-2027. Multiple trials are ongoing for obesity, type 2 diabetes, fatty liver disease, and other conditions.
You should NOT combine retatrutide with other GLP-1 (a gut hormone that tells your brain you're full) based medications like semaglutide or tirzepatide, because retatrutide already hits those targets 2. However, metformin and SGLT2 inhibitors (two kinds of diabetes drugs) were safely used alongside retatrutide in clinical trials.
Based on data from similar medications, some weight regain is expected after stopping 12. However, maintaining healthy lifestyle changes developed during treatment can help preserve results. Long-term maintenance strategies are still being studied.
Nausea is the most common side effect, affecting about 25-40% of users depending on dose. However, it's usually mild to moderate, improves with time, and is largely manageable by starting with low doses and increasing gradually. Most people find it tolerable given the significant weight loss benefits.
GLP-1 (a gut hormone that tells your brain you're full) class medications carry warnings about thyroid C-cell tumors based on rodent studies, but this hasn't been observed in humans 13. However, people with personal or family history of medullary thyroid carcinoma should not use retatrutide as a precaution.
While retatrutide produces significant weight loss even without intensive lifestyle intervention, combining it with healthy eating and regular physical activity maximizes results and helps maintain weight loss long-term. The medication makes dietary changes easier by reducing hunger and cravings.
Semaglutide targets only the GLP-1 (a gut hormone that tells your brain you're full) receptor and produces about 15-17% weight loss 1214. Retatrutide's triple mechanism delivers approximately 24% weight loss at the highest dose—about 40% more weight loss 1. However, semaglutide is FDA approved and available now, while retatrutide is still investigational.
14 sources
Every numbered marker on this page points to one of these. Same sources, same numbering as the Retatrutide research profile on Peptide Initiative.
Want the deep science?
Every claim on this page traces back to the research database behind Peptide Initiative — studies, citations, clinical trial data, and the technical detail we deliberately left out here.
Open the research profileThis guide is education, not medical advice. Retatrutide is a research compound that is not FDA-approved for human use. Talk to a clinician before taking anything.
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