Retatrutid

What is Retatrutide?

Retatrutide is an experimental peptide drug made by Eli Lilly. It's called a triple agonist because it activates three different receptors at the same time: those for the hormones GLP-1, GIP, and glucagon. The drug is in the final phase of clinical testing (Phase 3) and is not approved as a medication anywhere in the world yet.

Unlike well-known market leaders, this substance doesn't just affect one or two hormone systems. Semaglutide (Wegovy/Ozempic) is a pure GLP-1 agonist, and tirzepatide (Mounjaro) combines GLP-1 and GIP as a dual agonist. Retatrutide adds the glucagon receptor as a third mechanism. This extra target is meant to increase the body's energy expenditure and promote fat breakdown in the liver - a feature that sets it apart from all previously available drugs in this class.

How is Retatrutide used?

In all clinical studies, retatrutide is given as an injection under the skin (subcutaneous), once a week [1, 3, 5]. This is the same route as with semaglutide and tirzepatide. There is no oral, nasal, or topical form - neither in studies nor in gray market practice.

Since retatrutide is not approved, you can't get it through a pharmacy. On the gray market (so-called 'research chemicals'), it's sold as a lyophilized powder in vials. Users mix it with bacteriostatic water (BAC water) and then inject it subcutaneously. This practice is unproven and happens without medical supervision - we only document it here, we do not recommend it.

The half-life of retatrutide is about 6 days (~144 hours), which allows for weekly administration [1]. In the studies, the dose was gradually increased (titrated) over several weeks to minimize gastrointestinal side effects [1, 3].

From vial to use: calculating reconstitution and dose

Since retatrutide is only available as a powder vial in studies and on the gray market, it must be reconstituted (mixed) before use. The following calculation is a documenting example - not instructions or a recommendation.

Example calculation (unproven user practice, for documentation only):

• Vial: 10 mg retatrutide (lyophilized powder)
• Reconstitution with 2 mL BAC water -> concentration: 5 mg/mL
• Starting dose (study protocol): 2 mg -> 0.4 mL = 40 units on an insulin syringe (U-100)
• Target dose (study protocol): 12 mg -> 2.4 mL from this vial (at 5 mg/mL)

If you want to calculate a specific dose from a vial, you can use the Injection Calculator - you can enter the vial size, reconstitution volume, and target dose there, and the tool calculates the required syringe volume. Important: retatrutide is not approved, and this calculation does not replace medical advice.

Note on storage: After reconstitution, peptide solutions should be stored refrigerated (2-8 degrees Celsius) and protected from light. You can find details on proper mixing and storage in the Guides.

How does Retatrutide work?

Retatrutide sharpens three central metabolic levers at the same time: it demonstrably curbs appetite, improves insulin action, and - as a key special feature - increases energy expenditure and fat breakdown in the liver. This triple effect - GLP-1 for satiety, GIP for insulin and fat tissue, glucagon for energy expenditure - is what sets retatrutide apart from other drugs in this class.

The GLP-1 component slows stomach emptying and signals satiety to the brain - similar to semaglutide. The GIP component improves insulin action and influences fat metabolism. The glucagon arm - which is missing in semaglutide and tirzepatide - stimulates the liver to burn more fat and increases the basal metabolic rate. In combination, this leads to weight loss that in studies sometimes reaches the level of bariatric surgery.

How effective is Retatrutide?

Retatrutide shows exceptionally strong, dose-dependent weight loss in clinical studies, sometimes reaching the level of bariatric surgery. In Phase 3 studies, participants lost up to 30.3% of their body weight on the highest dose (12 mg) [5].

The key study results at a glance:

In type 2 diabetes, significant reductions in long-term blood sugar (HbA1c) were also observed. In TRIUMPH-2, the HbA1c reduction on 12 mg was up to -2.0 percentage points [8]. In addition, favorable effects on liver fat, blood pressure, and blood lipids were shown [3, 4]. A body composition substudy of Phase 2 confirmed that the weight loss came to a significant extent from fat mass (not muscle mass) [2].

The TRIUMPH study program

The TRIUMPH study program is the comprehensive Phase 3 program from Eli Lilly. It tests the efficacy and safety of retatrutide on various patient-relevant endpoints. The program includes four core studies with over 5,800 participants [3]:

• TRIUMPH-1 (NCT05929066): Obesity without type 2 diabetes (2,339 participants, 80 weeks, with 104-week extension). Results: May 2026 [5].
• TRIUMPH-2 (NCT05929079): Obesity with type 2 diabetes (1,152 participants, 80 weeks). Results: July 2026 [8].
• TRIUMPH-3 (NCT05882045): Obesity with cardiovascular disease (80 weeks). Results: July 2026 [8].
• TRIUMPH-4 (NCT05931367): Obesity with knee osteoarthritis (445 participants, 68 weeks). First Phase 3 results: December 2025 [4].

There are also additional studies (TRIUMPH-5 to -9), some of which are still ongoing or recruiting, including a head-to-head comparison with tirzepatide [6]. You can find more background on the study program in our news article on the TRIUMPH results.

Dosage: what the studies show - and the course

In the studies, retatrutide is injected subcutaneously once a week. The dose is gradually increased over several weeks to limit gastrointestinal side effects [1, 3, 5].

The titration schedule in the Phase 3 studies typically looks like this:

The doses studied include 0.5 mg, 1 mg, 2 mg, 4 mg, 6 mg, 8 mg, 9 mg, and 12 mg [1, 3, 5]. The most effective doses in Phase 3 were 9 mg and 12 mg. In TRIUMPH-1, an additional 4 mg maintenance dose was tested, which still achieved -19% weight loss after 80 weeks [5].

This is a purely reporting presentation of the study dosages - not a dosage recommendation. Retatrutide is not approved, and there is no validated dose for use outside of studies.

Side effects and common mistakes

The safety profile of retatrutide is considered moderate. The most common side effects in clinical studies were gastrointestinal events such as nausea, diarrhea, vomiting, and constipation. They occurred dose-dependently and led to treatment discontinuation [1, 3]. Discontinuation rates were higher on 12 mg than on 9 mg.

Two specific side effects set retatrutide apart from other GLP-1 drugs:

• Increased heart rate: An increase in heart rate of an average of 5-10 beats per minute was observed [1]. This is attributed to the glucagon receptor component.
• Skin hypersensitivity: Temporary skin reactions (redness, itching at the injection site or generalized) occurred in some patients [1].

In TRIUMPH-3, 27 MACE-3 events (cardiovascular deaths, heart attacks, strokes) were observed on 12 mg [8], which means cardiovascular safety requires further analysis.

Common mistakes in gray market practice include increasing the dose too quickly (which leads to stronger gastrointestinal complaints), incorrect reconstitution, and improper storage. If you still want to engage with the topic, you can find basic information on proper mixing and storage in the Guides.

Approval and legal status

Retatrutide is currently not approved as a medication in any country in the world. It is exclusively an experimental research substance in clinical studies [3, 5, 6].

Eli Lilly plans to submit a Biologics License Application (BLA) to the US FDA in the first quarter of 2027 - not, as previously assumed, an NDA in 2026 [8]. A regulatory decision is expected no earlier than the end of 2027. For Europe (EMA), approval is expected later.

Until then, the only legitimate access is participation in clinical studies. All other forms of procurement (gray market, 'research chemicals') are legally and health-wise risky. You can find more information on protecting yourself when ordering and recognizing dubious providers on the page about protection when ordering.