Retatrutide: The Triple Agonist That Could Change Weight Loss Treatment

Current GLP-1 medications are not the ceiling

There is a common assumption that today's GLP-1 medications represent the upper limit of what medication-assisted weight loss can achieve. Semaglutide delivers around 15% weight loss. Tirzepatide pushes that to roughly 22%. Those are strong numbers compared to what was possible five years ago. But they are not the ceiling.

Retatrutide, a medication currently in Phase 3 clinical trials, is challenging that assumption. In its latest trial, participants on retatrutide lost an average of 28.7% of their body weight over 68 weeks. That is nearly double what semaglutide achieves, and well ahead of tirzepatide.

The difference is in the mechanism. Where semaglutide targets one hormone receptor and tirzepatide targets two, retatrutide targets three. It is the first "triple agonist" for weight loss, and the early clinical evidence suggests that third receptor makes a real difference.

Retatrutide is not yet available in Singapore or anywhere else. It is still working through clinical trials and regulatory approvals. But if you are interested in where weight loss treatment is heading, and what options exist for you right now, this article covers everything we know so far.

What is retatrutide and how does it work?

Retatrutide is an investigational medication developed by Eli Lilly. It is a 39-amino-acid peptide designed to activate three hormone receptors simultaneously: the GLP-1 receptor, the GIP receptor, and the glucagon receptor. This is why researchers call it a "triple agonist" or "triple hormone receptor agonist."

To understand why three receptors matter, it helps to know what each one does.

GLP-1 (glucagon-like peptide-1) is the receptor targeted by medications like Wegovy and Ozempic. Activating it reduces appetite, slows gastric emptying so you feel fuller for longer, and improves blood sugar regulation. This is the "calories in" side of the equation.

GIP (glucose-dependent insulinotropic polypeptide) is the second receptor, already targeted by tirzepatide (Mounjaro). GIP activation improves insulin sensitivity and influences how the body processes fat. When combined with GLP-1, the two pathways amplify each other.

Glucagon is the third receptor, and this is what makes retatrutide different from everything currently available. Glucagon increases energy expenditure and promotes fat oxidation, meaning the body burns more stored fat for fuel. It also has direct effects on liver fat metabolism.

The result is a medication that works on both sides of the energy balance equation. GLP-1 and GIP reduce how much you eat. Glucagon increases how much energy your body burns. No previously approved obesity medication has combined all three pathways.

Retatrutide is administered as a once-weekly subcutaneous injection, similar to other GLP-1 medications. It has a half-life of approximately six days, which supports the weekly dosing schedule.

How retatrutide fits into the progression

Think of it as an evolution across three generations of weight loss medication:

• Generation 1 (single agonist): Semaglutide (Wegovy, Ozempic) targets the GLP-1 receptor alone
• Generation 2 (dual agonist): Tirzepatide (Mounjaro) targets GLP-1 + GIP receptors
• Generation 3 (triple agonist): Retatrutide targets GLP-1 + GIP + glucagon receptors

Each generation has produced greater weight loss in clinical trials. Adding each new receptor pathway appears to contribute noticeably to the results.

What the clinical trials show

Retatrutide has been studied in both Phase 2 and Phase 3 clinical trials, with data published in peer-reviewed journals and presented by Eli Lilly.

Phase 2 results (NEJM, 2023)

The Phase 2 trial (Jastreboff et al., New England Journal of Medicine, June 2023) tested multiple doses of retatrutide over 48 weeks in adults with obesity.

At the highest dose (12 mg), participants lost an average of 24.2% of their body weight in just 48 weeks. The response rates were unusually high:

• 100% of participants on 12 mg lost at least 5% of their body weight
• 93% lost at least 10%
• 83% lost at least 15%

A 100% response rate at the 5% threshold is unusual in obesity trials. Most medications see 60-70% of participants reaching that mark. This suggested the triple agonist mechanism was producing a different kind of response.

Phase 3 TRIUMPH-4 results (December 2025)

The first Phase 3 readout came from TRIUMPH-4, a trial enrolling 445 patients with obesity and knee osteoarthritis. The results, announced by Eli Lilly in December 2025, showed even stronger weight loss than Phase 2:

The 28.7% figure refers to participants who completed 68 weeks of treatment. The intention-to-treat analysis, which includes all enrolled participants regardless of whether they finished the study, showed 23.7% at the 12 mg dose.

Beyond weight loss, the TRIUMPH-4 trial also measured osteoarthritis pain. Participants experienced a 75% reduction in pain scores, a result that suggests the weight loss itself has clear clinical benefits for joint health.

Liver fat reduction

A separate Phase 2a study published in Nature Medicine (June 2024) tested retatrutide in patients with metabolic dysfunction-associated steatotic liver disease (MASLD, previously known as fatty liver disease).

At 24 weeks on the 12 mg dose:

• Liver fat decreased by 82.4%
• 86% of participants achieved normal liver fat levels (below 5%)

This liver-specific benefit is thought to come primarily from the glucagon receptor activation, which directly stimulates fat metabolism in the liver. It positions retatrutide as a potential treatment for liver disease as well as obesity, though this requires confirmation in larger trials.

How retatrutide compares to current medications

Because retatrutide, tirzepatide, and semaglutide have not been tested head-to-head in the same trial, any comparison requires caution. Different trials enrol different patient populations, use different designs, and run for different durations. With that caveat, here is how the numbers line up:

Two points are worth noting. First, retatrutide's Phase 2 results at 48 weeks already exceeded what semaglutide and tirzepatide achieve at 68-72 weeks. Second, the Phase 3 results at 68 weeks show further weight loss beyond the Phase 2 data, suggesting the medication continues to work well with longer treatment duration.

Again, these are cross-trial comparisons, not head-to-head data. The patient populations differ. TRIUMPH-4 enrolled patients with obesity and osteoarthritis specifically. Direct comparison trials between retatrutide and other medications would provide more definitive answers, and some may be planned.

Side effects and safety profile

Like all GLP-1 receptor agonists, retatrutide causes gastrointestinal side effects. The TRIUMPH-4 data for the 12 mg dose showed:

• Nausea: 43.2%
• Diarrhoea: 33.1%
• Constipation: 25.0%
• Vomiting: 20.9%

These rates are higher than what is typically seen with semaglutide or tirzepatide at their approved doses, though direct comparison is difficult because of differences in trial design and dose titration schedules. Most GI side effects with GLP-1 medications are most common during dose escalation and tend to improve over time.

A new signal: dysesthesia

TRIUMPH-4 identified a side effect not commonly seen with other GLP-1 medications. Dysesthesia, an abnormal skin sensation (tingling, numbness, or burning), occurred in 20.9% of participants on the 12 mg dose compared to 0.7% on placebo. This will need further investigation in the remaining Phase 3 trials to understand its frequency, severity, and whether it resolves over time.

Discontinuation rates

In TRIUMPH-4, 18.2% of participants on the 12 mg dose discontinued treatment, compared to 12.2% on the 9 mg dose and 4.0% on placebo. These rates are within the range seen for other GLP-1 medications but are worth monitoring as more trial data becomes available.

The full safety profile of retatrutide is still emerging. The TRIUMPH programme includes over 5,800 participants across eight or more trials. As more data is published throughout 2026, the picture of both benefits and risks will become clearer.

When will retatrutide be available in Singapore?

Retatrutide is not approved in any country and is not available for prescription anywhere in the world. Here is the expected timeline based on current information:

Current status (February 2026):
- Phase 3 TRIUMPH programme is underway with over 5,800 participants
- First Phase 3 results (TRIUMPH-4) were released in December 2025
- Additional Phase 3 trials cover obesity (TRIUMPH-1, TRIUMPH-2), cardiovascular outcomes (TRIUMPH-3), sleep apnoea, chronic low back pain, MASLD, and cardiometabolic outcomes

Expected milestones:
- Remaining Phase 3 readouts: throughout 2026
- NDA submission to FDA: late 2026 or Q1 2027
- Potential FDA approval: mid-to-late 2027 at the earliest
- Singapore HSA approval: 2028 or later

Singapore's Health Sciences Authority (HSA) typically reviews new medications after they have received approval from a major regulatory agency like the FDA or EMA. A Phase 1 pharmacokinetic study for retatrutide was conducted in Singapore, which may signal Eli Lilly's intent to seek approval in this market, but the regulatory timeline remains uncertain.

What this means for weight loss treatment in Singapore

Retatrutide's clinical data is promising. A medication that addresses obesity from both the appetite and energy expenditure sides would be a real addition to the field. But it remains investigational, and it will be at least two to three years before patients in Singapore could access it through normal prescription channels.

Effective weight loss medications are available right now. The same GLP-1 and dual agonist pathways that retatrutide builds upon are already helping patients in Singapore achieve sustained weight loss.

Currently available options include:

• Semaglutide (Ozempic, Wegovy, Rybelsus): The most widely studied GLP-1 medication, with clinical data showing approximately 15% weight loss. Available as both weekly injections and daily oral tablets.
• Tirzepatide (Mounjaro): The dual agonist targeting GLP-1 and GIP, with clinical data showing approximately 22.5% weight loss at the highest dose. You can read more in our Mounjaro guide for Singapore.

If you have been waiting for "the perfect medication" before starting treatment, consider that the medications available today are already producing significant results for many patients. And if retatrutide does become available in Singapore in the coming years, your doctor can discuss whether switching or adjusting your treatment makes sense at that point.

To compare current medications and understand which might be suitable for you, speaking with a doctor is the best first step.

Frequently asked questions about retatrutide

Is retatrutide approved in Singapore?

No. Retatrutide is currently in Phase 3 clinical trials and has not been approved by any regulatory authority worldwide. Singapore's HSA is unlikely to review it before 2028 at the earliest. There is no legal way to obtain retatrutide in Singapore at this time.

How is retatrutide different from Mounjaro (tirzepatide)?

Mounjaro is a dual agonist that targets the GLP-1 and GIP receptors. Retatrutide adds a third target, the glucagon receptor, making it a triple agonist. The glucagon component increases energy expenditure and promotes fat burning, particularly in the liver. In clinical trials, retatrutide has produced greater weight loss than tirzepatide, though the two have not been tested head-to-head.

What does the glucagon component do?

Glucagon is a hormone that triggers the body to release stored energy. When the glucagon receptor is activated, it increases energy expenditure (so your body burns more calories at rest) and stimulates fat oxidation, particularly in the liver. This "calories out" effect is what distinguishes retatrutide from medications that primarily work by reducing appetite.

Will retatrutide replace Wegovy and Mounjaro?

Unlikely. Different patients respond differently to different medications, and tolerability varies. Some patients may do better on semaglutide or tirzepatide, particularly those who experience more side effects with the triple agonist. Retatrutide is more likely to become an additional option rather than a replacement. Doctors will be able to match patients with the medication best suited to their needs.

Can I get retatrutide now?

No. The only way to access retatrutide currently is through clinical trials. If you are interested in long-term weight loss with GLP-1 treatment, proven options like semaglutide (Wegovy, Ozempic) and tirzepatide (Mounjaro) are available through licensed clinics in Singapore, including Trimly.

Retatrutide: what to remember

• Retatrutide is the first triple agonist for weight loss, targeting GLP-1, GIP, and glucagon receptors simultaneously
• Phase 3 data (TRIUMPH-4) showed 28.7% weight loss at 68 weeks on the 12 mg dose
• The glucagon receptor component increases energy expenditure and reduces liver fat (82.4% liver fat reduction in a separate trial)
• Side effects include GI symptoms common to all GLP-1 medications, plus a new signal of dysesthesia (abnormal skin sensation) in about 21% of participants
• Retatrutide is not yet approved anywhere. Singapore availability is estimated at 2028 or later
• Effective weight loss medications, including semaglutide and tirzepatide, are available in Singapore right now

Retatrutide is not yet approved by the Health Sciences Authority (HSA) in Singapore and is not available for prescription. The clinical trial results discussed in this article are preliminary and may not reflect the final safety and efficacy profile of the medication. Clinical trial results are based on controlled study conditions and may not reflect real-world outcomes. Weight loss results vary depending on individual factors including starting weight, adherence, diet, and exercise. This article is for informational purposes only and does not constitute medical advice. Always consult your doctor before starting, stopping, or changing any medication. Trimly is a MOH-licensed telehealth clinic in Singapore (HCSA License R/25M0505/MDS/001/252).