Retatrutide (GLP-3RT) is a subcutaneous peptide that must be taken only once a week and that simultaneously acts on the three metabolic receptors GLP-1R, GIPR and glucagon receptor (GCGR). It is based on this ability to act simultaneously on three targets that it demonstrates better results than dual agonists during early clinical trials. The GLP-1 mechanism is responsible for slowing gastric emptying and for inhibiting appetite signaling in the hypothalamus; the GIP mechanism is responsible for enhancing insulin secretion by improving the overall sensitivity of the GLP-1 receptor. But the special role in this mechanism is played by the effect of glucagon: GCGR activation increases resting energy expenditure and enhances fat oxidation in the liver. This unique feature is the reason why retatrutide is being tested not only for obesity but for metabolic liver disease (MASLD) and type 2 diabetes.
Researchers introduced the term "GLP-3" to make it easy to remember the molecule's identity since it is part of an agonist series of compounds. The compound is called LY3437943 by Lilly. The TRIUMPH phase 2 study provides the primary published information available.
One point that deserves mentioning for newcomers to this field of research: glucagon stimulation may sound contradictory as glucagon raises blood glucose levels. It does so in isolation. With triple agonists, the impact of GLP-1 and GIP reduces post-meal blood sugar levels. The end result in the TRIUMPH study was a notable improvement in glycemic parameters along with weight loss. The main task of glucagon in terms of the data was to improve energy expenditure and liver fat levels, not to increase blood sugar levels.
According to TRIUMPH phase 2 trial published in NEJM 2023 (Jastreboff et al.), the main finding indicates a 24.2% mean reduction in body weight at the 48th week on the weekly dose of 12 mg. It is a result of the placebo-controlled experiment with a sample size of 338 subjects suffering from obesity. The 8 mg dose produced a positive result of 22.8% and 4 mg dose has recorded 17.3%. The placebo group had the result of 2.1%. These numbers are often referred to in GLP-3 discussions and represent the largest dataset of humans analyzed so far.
Aside from weight loss, the TRIUMPH program reported a reduction of waist circumference, plasma insulin, triglyceride levels and liver fat assessed via MRI-PDFF in a selected group of patients. In the separate phase 2 study in individuals with type 2 diabetes, the decreases in HbA1c values reached 2.02%. Phase 3 results are expected in 2025-2026; that allows regulatory information to change in the upcoming 12-18 months.
What is not evident from the trial: long-term cardiovascular effects (CVOT has yet to be completed), safety beyond 48 weeks for people suffering from obesity, or effectiveness for excluded populations (those with a previous case of pancreatitis, a case of MEN2, or one that can lead to medullary thyroid cancer). Researchers who model procedures based on the information have to treat these missing elements as real uncertainties rather than as questions already answered in forums.
According to the TRIUMPH study, significant weight loss from the placebo was seen at week 12, with the steepest rate occurring in the period from weeks 12 to 36. This compound has a half-life of about 6 days, meaning that the agent can be given once a week. Since 4-5 half-lives are required to achieve steady state, the researchers who expect to see results by week 2 do not understand pharmacokinetics.
On the issue of women-related claims in online forums: TRIUMPH failed to disclose weight loss data according to gender in its initial findings. Claims alluding to GLP-3 functioning differently in terms of males and females are unsupported by the results of the research. This is a question we receive frequently, and the answer is simple: data related to the group is not yet available.
The Lilly investigational product is presented as subcutaneous injection. The research-supply market has other delivery forms such as nasal or spray, but none is for retatrutide specifically. Subcutaneous injection is the sole procedure with available human data. The table below shows the known versus the unknown.
| Format | Bioavailability Data | Used in Trials | Available at US Peptide Labs |
|---|---|---|---|
| Subcutaneous Injection (lyophilized powder reconstituted) | Yes - phase 2 and phase 3 trials. | Yes (TRIUMPH). | GLP-3RT 10/20/40 mg vials. |
| Nasal Spray | No published data for retatrutide. | No. | GLP-3RT Nasal Spray from $220. |
| Oral Spray | No published data for retatrutide. | No. | GLP-3RT Oral Spray from $220. |
When it comes to research, it is the injection format that serves as the gold standard. To make it easier for researchers working with an alternative form of delivery, nasal and oral sprays are available, so the final say in the overall effectiveness of any method goes to those using the term injection in their reports about trial results.
The TRIUMPH trial involved the implementation of a four-level dosage scheme: 1 mg, 4 mg, 8 mg, and 12 mg once a week subcutaneously. Dosing started with 1-2 mg and increased every four weeks. Below is a table showing the progress of the trial as well as the data related to the vial of 10 mg, 20 mg, and 40 mg from US Peptide Labs, assuming that 2 ml of bacteriostatic water are used for reconstitution process. You can find custom vial calculations on peptide dosage calculator and complete protocol summary on retatrutide dosage reference page.
| Trial Dose (Weekly) | 10 mg Vial / 2 ml BAC (5 mg/ml) - Volume | 20 mg Vial / 2 ml BAC (10 mg/ml) - Volume | 40 mg Vial / 2 ml BAC (20 mg/ml) - Volume |
|---|---|---|---|
| 1 mg | 0.20 ml (20 units on a 100-unit syringe). | 0.10 ml (10 units). | 0.05 ml (5 units). |
| 4 mg | 0.80 ml (80 units). | 0.40 ml (40 units). | 0.20 ml (20 units). |
| 8 mg | 1.60 ml (160 units - requires 2 injections from a 10 mg vial). | 0.80 ml (80 units). | 0.40 ml (40 units). |
| 12 mg | Not achievable from a single 10 mg vial. | 1.20 ml (120 units). | 0.60 ml (60 units). |
It should be noted that 8 mg per week works out to a volume of 10 mg in 2 ml however it might be above the limit of how much a vial can provide per injection. Studies where dose protocol ranges from 8 mg to 12 mg per week have used 20 mg or 40 mg vials to eliminate the partial vial problem. While 40 mg vials worth 300 dollars last approximately 3.3 weeks at 12 mg, it may be an appropriate approach for the purposes of high-dose protocols.
The TRIUMPH protocol did not restrict the timing of injections to either the morning or evening, but instead used a weekly schedule as the controlled variable. Given that the half-life is approximately six days, any variation in the time-of-day will have little pharmacokinetic significance. In research protocols, injection timing usually follows the weekly fixed-day approach used in the trial.
Reconstitution: add 1-2 ml of bacteriostatic water with no shaking, but swirling gently. Store the vials once reconstituted at 2-8 C in a refrigerator and do not freeze. Keep the lyophilized powder in a refrigerator and away from light before reconstitution. The dosage calculator at Get US Peptides is capable of handling any vial size and target dosage combination. During the study, subcutaneous injection sites were used in abdomen, thigh or upper arm and the injections were rotated weekly.
The published data has a cycle length of 48 weeks. A research duration of less than 12 weeks will not capture the entire dose-response curve seen in TRIUMPH, in which maximum weight loss occurred between weeks 12 and 36.
Retatrutide is being analyzed among other metabolic agents in the research community. The most logical combination with it in the literature is with agents aimed at insulin sensitivity or liver metabolism. Tirzepatide, which is a dual GLP-1 and GIP receptor agonist, is the predecessor in the receptor stacking process. We have Tirzepatide from $76 at US Peptide Labs for researchers who would like to compare dual and triple agonism directly.
No human data on combining retatrutide with other peptides has been published so far. Stacking GLP-class compounds with overlapping receptor targets increases the chance of experiencing side effects, specifically GI side effects, however, there is no data that demonstrates the effect of the combination. The researchers devising the combination protocol have to consider this variable rather than treat it as solved. The source GLP-1 weight management collection lists the existing comparators.
The TRIUMPH study disclosed a distinct side effect profile with nausea, vomiting, diarrhea and constipation being the most common side effects. Side effects were dose-dependent and observed at every dose of titration. At 12 mg, 42% of subjects experienced nausea as compared to 9% on placebo. The adverse effects were mostly mild or moderate in severity and resolved in 1-2 weeks after reaching a stable dose. The phenomenon of tachycardia (mean +2-4 bpm above initial rate) was also noted, which is in line with the action of GLP-1 agonists.
Sensory issues on the skin (i.e. reactions at injection sites, itchiness) were experienced by only a small fraction of research subjects. There has not been reported any signs of liver toxicity in the phase 2 study results. The thyroid C-cell side effects, which have been established as a potential problem for GLP-1 receptor agonists in animal studies, have yet to impact human subjects but there is no data in this respect in the long term.
A few exclusions apply to a retatrutide research study, such as individuals with a personal or familial history of medullary thyroid cancer, any cases of MEN2 syndrome, and a history of pancreatic inflammation. These are the same exclusion criteria used in TRIUMPH and the general GLP-1 agent group of drugs.
The drug retatrutide hasn't undergone approval by the FDA. It is still in the investigational stage, under Eli Lilly's IND, and is presently being studied in relation to Phase 3 trials until 2025-2026. It is not a part of the FDA's 503A Bulk Drug Substances list that allows formulations to be made in American pharmacies. As of 2026, FDA's Pharmacy Compounding Advisory Committee doesn't include retatrutide in its reviews for inclusion within the 503A list.
It is stated that US Peptide Labs does not market its products as a drug and that GLP-3RT is sold as a research chemical only. Furthermore, US Peptide Labs operates just as a chemical supplier and not as a 503A or 503B pharmacy. In addition, the buyers need to be over the age of 21 years in order to buy the products and use the product solely for research purposes. Also, Retatrutide is not banned by the latest published WADA list.
Reality of 2026: if phase 3 results prove to be positive and Lilly submits an NDA, then the regulatory situation will change. Until then, the drug exists only as an investigational medicine in Lilly’s studies as well as a research product on the market.
The most typical comparison made in the GLP-class domain is between the drugs retatrutide and semaglutide (which binds to one receptor) and tirzepatide (that binds to a couple of receptors). The following chart uses the published trial data of all three. The semaglutide library page and tirzepatide library page sources have the full profile of receptors for these compounds.
| Compound | Receptors Targeted | Peak Trial Weight Loss (human, phase 2/3) | Dosing Interval | FDA Status (2026) |
|---|---|---|---|---|
| Semaglutide (Wegovy) | GLP-1R (1 receptor). | ~15% at 68 weeks (STEP 1). | Once weekly SC. | FDA approved (obesity, T2D). |
| Tirzepatide (Zepbound) | GLP-1R + GIPR (2 receptors). | ~20.9% at 72 weeks (SURMOUNT-1). | Once weekly SC. | FDA approved (obesity, T2D). |
| Retatrutide / GLP-3RT | GLP-1R + GIPR + GCGR (3 receptors). | 24.2% at 48 weeks (TRIUMPH phase 2). | Once weekly SC. | Investigational - not approved. |
The figure of 24.2% for retatrutide is based on a Phase 2 trial which consists of a smaller and shorter dataset than those Phase 3 trials used to support the approval of semaglutide and tirzepatide. Therefore, comparisons should be made with the consideration of this difference in methodology in mind. Phase 3 data will tell the real story.
US Peptide Labs has both GLP-3RT and LY3437943 as products in their store as both are the same compound sold under two of the common names used by researchers for that compound. Another GLP-3RT product available at their store is the GLP-3RT Nasal Spray available for a price of $220 for the consumption of non-injection delivery by researchers.
Pricing as listed:
| Vial Size | Single Unit | 2+ Units | 5+ Units |
|---|---|---|---|
| 10 mg Vial | $100.00. | $95.00. | $90.00. |
| 20 mg Vial | $170.00. | - | - |
| 40 mg Vial | $300.00. | - | - |
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At US Peptide Labs, the term "lab tested" indicates a specific certificate of analysis that has been issued by AxisPharm, which is an independent laboratory. In total, there are 13 lots recorded. The vial base should have a lot number on it that matches the one on the COA before the vial is opened. I have personally accessed the AxisPharm COAs and have found that the purity is more than 99%. You can find the lot documents on the COA page at the store and the COA reading guide at Get US Peptides explains you everything.
One common issue that arises is when researchers tend to order a 10 mg vial for a 12 mg dosage protocol, thereby leading them to run into the vial math problem that has been elucidated in the dosage section. The 40 mg vial is the appropriate one for that dosage tier. Check the peptides for weight loss research guide for more information regarding where retatrutide is positioned in the compound's spectrum.
According to studies, retatrutide (GLP-3RT) is in trial investigations against obesity, type 2 diabetes, and metabolic liver disease (MASLD). The main phase 2 trial - TRIUMPH study - is the first human evidence available, with data showing significant weight reduction - max 24.2% by week 48. Trials of phase 3 are being conducted. retatrutide is only available for research purposes and not to be administered by humans, per the US Peptide Labs specifications.
In all the accomplished studies, Retatrutide is not given every day, just once a week. The TRIUMPH program comprised of the dosages of 1 mg, 4 mg, 8 mg, and 12 mg, which were intensified in four-week intervals. The research protocols include the same schedule. The time of administering the drug was not an influencing factor in this trial. Use the web link to find out the quantity of injection required for any size of vial.
No bioavailability records have been published concerning oral or nasal usage of retatrutide. All human clinical data, including the reported 24.2% weight loss, derive from subcutaneous injection. Oral and nasal spray formulations can be found at US Peptide Labs for researchers interested in alternative administration, but efficacy comparison with injectable formulations is not made in the available literature.
There is no human data in the published literature that supports or characterizes the use of retatrutide in combination with other peptides. The combination of GLP-class agents with overlapping receptor targets increases the risk of gastrointestinal side effects, but there isn't any known additive efficacy for this approach. The researchers working on combination protocols are using information other than the one that is available in the published literature.
Retatrutide has not yet received FDA approval. This medicine is currently going through the stage 3 research program by Eli Lilly. As Retatrutide is not included in the 503A Bulk Drug Substances list, it cannot be used in compounding systems. US Peptide Labs produces and distributes the drug for scientific purposes. Currently, there is no information on Retatrutide being included in the WADA banned substances list.
The receptivity and results of trials for GLP-3 (retatrutide) and semaglutide are different. The mechanism of semaglutide involves targeting one receptor (GLP-1R) and is well established as causing around 15% weight loss in the STEP 1 Phase 3 trial. Retatrutide on the other hand targets three receptors hence weighing 24.2%. Semaglutide is approved by the FDA while retatrutide is investigational. The fact that the retatrutide molecule includes glucagon receptor is the key factor making it superior in terms of inducing higher energy expenditure and fat in the liver reduction.
View GLP-3RT at US Peptide Labs - 99%+ Purity, AxisPharm COA, US Shipping - 5% Off 2+ Units