What the SYNCHRONIZE-1 trial found
Phase 3 trials are the large, late-stage human studies that regulators rely on to decide whether to approve a new medication.
SYNCHRONIZE-1 is the first Phase 3 trial in survodutide’s obesity programme to deliver results.
Survodutide is being developed by Boehringer Ingelheim in collaboration with Zealand Pharma. It’s a once-a-week subcutaneous injection.1
The trial enrolled 725 adults with obesity (BMI 30 or above) or overweight (BMI 27 or above with at least one weight-related complication), without type 2 diabetes.
Participants had a mean BMI of 37.9 and a mean age of 47, and were enrolled across 14 countries. Around 59% were women.
Participants were randomised to placebo or to one of two survodutide doses (3.6 mg or 6.0 mg) for 76 weeks. The doses were increased gradually over an extended period to limit side effects.
Participants on the higher 6.0 mg dose lost an average of 16.6% of body weight, compared with 3.2% on placebo.
85.1% of participants on survodutide achieved at least 5% weight loss, compared with 38.8% on placebo.1
The 16.6% figure refers to participants who completed the full 76 weeks of treatment.
Boehringer also reported that the result was statistically significant when including everyone who started the trial, regardless of whether they stopped taking the medication, but the specific percentage from this second analysis hasn’t been published.
The full trial data, including waist circumference, glycaemic markers, and detailed adverse events, are expected to be presented at the American Diabetes Association Scientific Sessions in June 2026.
How survodutide works
Survodutide mimics two hormones our body naturally produces in response to food: GLP-1 and glucagon.
GLP-1 (glucagon-like peptide-1) lowers hunger, slows down stomach emptying, and helps the pancreas release insulin in response to food. This is the same hormone that Wegovy, Ozempic, and Mounjaro mimic.
Glucagon raises blood glucose by triggering the liver to release stored sugar. It also encourages the body to burn more fat and increases energy expenditure.
Survodutide mimics both hormones at once. The GLP-1 component lowers hunger in a similar way to Wegovy.
Adding glucagon has additional effects on energy expenditure and on fat metabolism in the liver.2
This second mechanism is why Boehringer has also been testing survodutide for metabolic dysfunction-associated steatohepatitis (MASH), a serious liver disease formerly called NASH.
A Phase 2 study published in the New England Journal of Medicine in 2024 found that survodutide produced significant improvements in liver fat and inflammation markers, which led the FDA to award the drug Breakthrough Therapy designation for MASH in October 2024.2
Mounjaro and Wegovy take different approaches. Mounjaro (tirzepatide) mimics GLP-1 and a second hormone called GIP (glucose-dependent insulinotropic polypeptide), which enhances insulin sensitivity rather than energy expenditure. Wegovy (semaglutide) mimics GLP-1 alone.
Retatrutide, an experimental drug from Eli Lilly currently in Phase 3 trials, mimics three receptors at once: GLP-1, GIP, and glucagon.
Phase 2 data published in 2023 showed a weight loss of approximately 24% at 48 weeks in the highest-dose group. Phase 3 data aren’t yet available.3
How it compares to Mounjaro and Wegovy
The most useful comparison is what the major Phase 3 trials of these medications have shown for weight loss in adults without type 2 diabetes.
| Drug (developer) |
Mechanism |
Trial |
Mean weight loss vs placebo |
Status |
Survodutide
(Boehringer / Zealand) |
GLP-1 + glucagon |
SYNCHRONIZE-1
n=725, 76 weeks |
Up to 16.6% vs 3.2%
(6.0 mg dose)1 |
Phase 3 readout April 2026; not yet filed for approval |
Mounjaro
(Eli Lilly) |
GLP-1 + GIP |
SURMOUNT-1
n=2,539, 72 weeks |
20.9% vs 3.1%
(15 mg dose)4 |
MHRA-approved; available privately and via NICE-approved NHS pathway |
Wegovy 2.4 mg
(Novo Nordisk) |
GLP-1 only |
STEP-1
n=1,961, 68 weeks |
14.9% vs 2.4%5 |
MHRA-approved; available privately and via NICE-approved NHS pathway |
Wegovy 7.2 mg
(Novo Nordisk) |
GLP-1 only (higher dose) |
STEP UP
n=1,407, 72 weeks |
20.7% vs 2.4%6 |
Filed for EU label expansion in January 2025; UK approval expected to follow |
CagriSema
(Novo Nordisk) |
GLP-1 + amylin |
REDEFINE-1
n=3,400, 68 weeks |
20.4% vs 3.0%7 |
FDA decision expected around October 2026; not yet UK-licensed |
Cross-trial comparisons are difficult to interpret directly. The trials enrolled different populations, used different durations, and reported their primary endpoints (like weight loss) in different ways.
There’s no direct head-to-head trial of survodutide against tirzepatide or semaglutide, and none has been announced.
Without a head-to-head trial, the data suggest survodutide produces less weight loss on average than Mounjaro, Wegovy 7.2 mg, and CagriSema, but more than Wegovy at the licensed 2.4 mg dose.
Industry analysts at Fierce Biotech noted that the placebo-adjusted weight loss in SYNCHRONIZE-1 (13.4%) was similar to Wegovy 2.4 mg’s placebo-adjusted figure of 12.4% in STEP-1.
With the higher 7.2 mg dose of Wegovy now showing 18.3% placebo-adjusted weight loss, survodutide’s competitive position has narrowed further over the past year.
When could survodutide be available in the UK?
Boehringer hasn’t filed an application for survodutide for obesity in any major market.
A realistic timeline based on current Phase 3 progress:
- FDA New Drug Application: late 2026 or early 2027
- FDA approval (USA): late 2027 or 2028
- UK MHRA review: typically 12 to 24 months after FDA approval
- NHS access via NICE Technology Appraisal: separate process, usually 12 to 24 months after MHRA authorisation
The earliest UK private access via online pharmacies, mirroring how Mounjaro and Wegovy launched in the UK, is likely 2027 or 2028. NHS access would come later.
Survodutide is being developed in parallel for MASH, the liver condition mentioned earlier.
The MASH programme has its own Phase 3 trials (LIVERAGE and LIVERAGE-Cirrhosis) and could potentially reach approval on a different timeline to the obesity indication.2
Survodutide doesn’t yet have a brand name. In trial documents and press materials, it’s referred to either as ‘survodutide’ or by its development code, BI 456906.
What this means if you’re on Mounjaro or Wegovy
In the short term, the SYNCHRONIZE-1 results don’t change anything practical for people currently taking Mounjaro or Wegovy.
Survodutide isn’t approved or available in the UK and won’t be for at least 18 to 24 months.
It’s fair to say that the obesity medication market is becoming more crowded.
Three medications (tirzepatide, semaglutide 2.4 mg, and semaglutide 7.2 mg) are already approved or filed for approval.
Three more (survodutide, retatrutide, and mazdutide from Innovent) are in late-stage development.
When multiple medications are effective, the question shifts from whether to use one to which one suits an individual best.
For now, the practical question is whether your current medication is working.
If you’re losing weight at a sustainable rate, tolerating the side effects, and supported by structured behaviour change, switching makes little sense.
If you’re not responding well to one GLP-1 medication, there are now more options available if you were to consider switching.
Some people lose more weight on tirzepatide than on semaglutide, others tolerate one better than the other, and side effects vary between medications.
Talk to a healthcare professional before changing or stopping any prescribed medication.
Limitations of the SYNCHRONIZE-1 results
SYNCHRONIZE-1 is the first Phase 3 trial in survodutide’s obesity programme. Boehringer has released topline numbers via a press release.
Detailed trial findings, including safety, dropout rates, and secondary endpoints, are expected at the American Diabetes Association Scientific Sessions in June 2026.
A peer-reviewed publication usually follows within weeks of a conference presentation.
The 16.6% figure refers to participants who completed the 76 weeks of treatment.
The figure that includes everyone who started the trial, regardless of whether they stopped taking the drug, is typically a few percentage points lower in trials of this kind, and the specific number hasn’t yet been disclosed.
There’s no head-to-head comparison with tirzepatide or semaglutide.
The trials enrolled different populations, used different trial durations (68, 72, and 76 weeks), and reported their results in different ways.
A 2 to 3 percentage-point difference between trials may reflect study design differences rather than a real difference in how the medications perform in the real world.
Adverse events are described as ‘mild to moderate’ and consistent with the GLP-1 class.
Specific rates of nausea, vomiting, and diarrhoea, and discontinuation rates, haven’t been released.
In the earlier Phase 2 study, dropout rates due to gastrointestinal side effects were considerably higher with survodutide than with placebo, mostly during the dose-escalation period.2
The slower dose increase used in SYNCHRONIZE-1 may have improved this, but the data hasn’t been published yet to confirm.
The trial was funded by Boehringer Ingelheim. It’s standard for Phase 3 trials to be sponsor-funded, but it’s useful context when interpreting topline figures released through a press release rather than a peer-reviewed journal.
The trial enrolled adults without type 2 diabetes. SYNCHRONIZE-2, in adults with obesity and type 2 diabetes, is currently running and is expected to deliver results later in 2026.
Take home message
Boehringer Ingelheim and Zealand Pharma reported on 28 April 2026 that survodutide produced up to 16.6% mean weight loss at 76 weeks in adults living with obesity at the higher dose tested, compared with 3.2% on placebo.
The trial met both co-primary endpoints, and 85.1% of participants achieved at least 5% weight loss.
The result puts survodutide ahead of Wegovy at the licensed 2.4 mg dose (14.9%, STEP-1), but several percentage points lower than Mounjaro (20.9%, SURMOUNT-1), Wegovy at the higher 7.2 mg dose (20.7%, STEP UP), and CagriSema (20.4%, REDEFINE-1, awaiting an October 2026 FDA decision).
Survodutide hasn’t been filed for approval anywhere yet. Realistic UK availability, first via private prescription and then via the NHS, isn’t expected until 2027 or 2028.
The full SYNCHRONIZE-1 data are expected at the American Diabetes Association Scientific Sessions in June 2026, including secondary endpoints, side effects, and the analysis that includes participants who stopped taking the medication.
If you’re already on Mounjaro or Wegovy and your medication is working, this announcement doesn’t change anything practical for you.
As more medications become available, the more useful question is which one suits which person, and what someone is doing alongside the medication to make the weight loss last.
At Second Nature, we support members through medication-supported weight loss programmes that combine evidence-based behaviour change with dietitian-led coaching, daily food and habit tracking, and a strong focus on protecting muscle mass during rapid weight loss.
Our published research found that members taking semaglutide alongside this support achieved an average of 19.1% weight loss at 12 months, with 77.7% reaching at least 10% weight loss.8
Second Nature's Mounjaro and Wegovy programmes
Second Nature provides Mounjaro or Wegovy as part of our Mounjaro and Wegovy weight-loss programmes.
Why choose Second Nature over other medication providers, assuming you're eligible?
Because peace of mind matters.
We've had the privilege of working with the NHS for over eight years, helping people across the UK take meaningful steps toward a healthier, happier life.
Our programmes are designed to meet people where they are, whether that means support with weight loss through compassionate one-to-one health coaching, or access to the latest weight-loss medications (like Mounjaro and Wegovy) delivered alongside expert care from a multidisciplinary team of doctors, psychologists, dietitians, and personal trainers.
At the heart of everything we do is a simple belief: real, lasting change comes from building better habits, not relying on quick fixes. We're here to support that change every step of the way.
With over a decade of experience, thousands of lives changed, and a long-standing record of delivering programmes used by the NHS, we believe we're the UK's most trusted weight-loss programme.
We hope to offer you something invaluable: peace of mind, and the support you need to take that first step.
References
- Boehringer Ingelheim / Zealand Pharma. (2026). Boehringer Ingelheim’s novel glucagon/GLP-1 dual agonist survodutide achieved significant weight loss of 16.6%, delivering meaningful metabolic improvement. Press release, 28 April 2026.
- Sanyal, A.J., et al. (2024). A phase 2 randomized trial of survodutide in MASH and fibrosis. New England Journal of Medicine, 391(4), 311-319.
- Jastreboff, A.M., et al. (2023). Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial. New England Journal of Medicine, 389(6), 514-526.
- Jastreboff, A.M., et al. (2022). Tirzepatide once weekly for the treatment of obesity. New England Journal of Medicine, 387(3), 205-216 (SURMOUNT-1).
- Wilding, J.P.H., et al. (2021). Once-weekly semaglutide in adults with overweight or obesity. New England Journal of Medicine, 384(11), 989-1002 (STEP-1).
- Wharton, S., et al. (2025). Once-weekly semaglutide 7·2 mg in adults with obesity (STEP UP): a randomised, controlled, phase 3b trial. Lancet Diabetes & Endocrinology, 13(11), 949-963.
- Garvey, W.T., et al. (2025). Coadministered cagrilintide and semaglutide in adults with overweight or obesity. New England Journal of Medicine (REDEFINE-1).
- Richards, R., et al. (2025). A remotely delivered, semaglutide-supported specialist weight management program: 12-month outcomes. JMIR Formative Research, 9(1), e72577.
