Survodutide Phase 3: What SYNCHRONIZE-1 Found

Survodutide is now one of the more advanced investigational obesity peptides. It combines glucagon receptor activity with GLP-1 receptor activity, and the first published Phase 3 obesity trial has confirmed that the drug can produce greater weight loss than placebo. The important part is not simply that the trial was positive. It is understanding what the numbers mean, why two different weight loss percentages are being quoted, and what the trial still does not tell us.

What is survodutide?

Survodutide, previously called BI 456906, is a long acting dual agonist at the glucagon receptor and the GLP-1 receptor. Boehringer Ingelheim is developing it globally under licence from Zealand Pharma. Zealand currently describes survodutide as investigational and in Phase 3 development for obesity and metabolic dysfunction associated steatohepatitis, usually shortened to MASH Mechanistic ¹.

GLP-1 receptor activity is already familiar from medicines such as semaglutide and tirzepatide. It can reduce appetite and food intake. The glucagon side is different. Glucagon signalling can increase energy expenditure and has direct metabolic effects in the liver. The idea behind survodutide is to combine those two actions rather than rely on GLP-1 signalling alone.

That mechanism is scientifically interesting, but Phase 3 clinical data are what matter for deciding whether it produces a useful treatment effect in people.

What did SYNCHRONIZE-1 test?

SYNCHRONIZE-1 was a Phase 3, randomised, double blind, placebo controlled trial in adults with obesity or overweight without type 2 diabetes. The study enrolled 725 participants across 14 countries. Participants had a body mass index of at least 30, or at least 27 with an obesity related complication Human ².

Participants were assigned to one of three groups:

survodutide up to 3.6 mg once weekly;
survodutide up to 6.0 mg once weekly; or
placebo once weekly.

All groups also received counselling for lifestyle modification. The treatment period lasted 76 weeks. The two primary endpoints were percentage change in body weight and the proportion of participants who lost at least 5% of baseline body weight Human ³.

The average participant entered the trial at 108.8 kg with an average BMI of 37.9. The mean age was 47.1 years.

The published Phase 3 weight loss result

The published primary analysis used what the investigators call a treatment regimen estimand. This analysis includes the effects of treatment discontinuation, use of prohibited obesity medicines and prolonged dose escalation. In other words, it is intended to reflect what happened across the treatment strategy rather than only among people who stayed continuously on the assigned treatment.

At week 76, mean body weight change was:

12.2% reduction with survodutide 3.6 mg;
13.0% reduction with survodutide 6.0 mg; and
5.4% reduction with placebo.

The differences versus placebo were statistically significant Human ².

The proportion of participants losing at least 5% of baseline body weight was 72.6% with 3.6 mg, 71.9% with 6.0 mg and 46.3% with placebo. Again, both survodutide groups were significantly different from placebo.

Those are the figures from the final peer reviewed Phase 3 publication.

Why did the earlier headline say 16.6%?

Before the full paper appeared, company announcements highlighted a different number: up to 16.6% average weight loss with survodutide versus 3.2% with placebo after 76 weeks ⁴.

That figure used an efficacy estimand. The company described it as estimating the treatment effect assuming participants remained on treatment for the study duration. It is therefore answering a different question from the treatment regimen estimand.

This is why both 13.0% and 16.6% can be correct without contradicting each other.

The 13.0% figure asks something closer to: what was the average result of the assigned treatment strategy, including interruptions and discontinuations?

The 16.6% figure asks something closer to: what effect would be expected if participants stayed on treatment as intended?

For readers comparing obesity trials, mixing those two estimands can create misleading comparisons. The analysis method matters as much as the headline percentage.

Did the 6.0 mg dose clearly beat 3.6 mg?

Not in the published treatment regimen result. Mean weight reduction was 12.2% with 3.6 mg and 13.0% with 6.0 mg. The proportions reaching at least 5% weight loss were also very similar, at 72.6% and 71.9%.

That does not mean the doses are identical. Dose response can look different across endpoints or analysis sets. It does mean that the Phase 3 publication does not support a simple assumption that the higher dose automatically produces a dramatically larger average benefit for every participant.

What happened with side effects?

Gastrointestinal symptoms were the most common adverse events, which is consistent with other obesity medicines that activate the GLP-1 receptor.

In SYNCHRONIZE-1, gastrointestinal adverse events occurred in 80.9% of participants in the 3.6 mg group, 89.7% in the 6.0 mg group and 47.9% in the placebo group Human ³.

The paper describes these events as typically mild to moderate. No deaths were reported.

The frequency still matters. A treatment can be effective and also difficult for some people to remain on. That is one reason the difference between efficacy and treatment regimen analyses is useful rather than academic.

What about visceral fat and liver fat?

A prespecified imaging substudy added another layer to the Phase 3 result. Zealand reported that among participants with MRI measurements, survodutide was associated with relative reductions of up to 34.0% in visceral fat and up to 63.1% in liver fat. At the highest dose, lean mass accounted for no more than 10.8% of the change in total tissue mass in that analysis Human ⁵.

Those findings are interesting because survodutide is being developed around more than body weight alone. Glucagon receptor activity is partly intended to influence liver metabolism, and the wider development programme includes metabolic liver disease.

A substudy is not the same as the main randomised trial population, so those percentages should not be treated as if every participant experienced them.

How does Phase 3 compare with the earlier Phase 2 trial?

The earlier obesity Phase 2 trial randomised 387 adults without diabetes and tested several survodutide doses over 46 weeks. In the planned treatment analysis, the highest 4.8 mg dose produced mean weight loss of 14.9% compared with 2.8% for placebo Human ⁶.

An on treatment analysis reported a larger figure, reaching 18.7% at the highest dose. Again, this is a good example of why analysis populations matter.

Phase 3 did not simply repeat the Phase 2 number. It tested a larger population, longer treatment, different target doses and a prespecified analysis strategy. The result remained positive, but the treatment regimen estimate was more modest than the largest on treatment Phase 2 figure.

What has survodutide shown in MASH?

Survodutide also has randomised human data in MASH. A 48 week Phase 2 trial enrolled 293 treated participants with biopsy confirmed MASH and fibrosis stages F1 to F3. Improvement in MASH without worsening fibrosis occurred in 47% of participants receiving 2.4 mg, 62% receiving 4.8 mg, 43% receiving 6.0 mg and 14% receiving placebo Human ⁷.

Fibrosis improvement by at least one stage occurred in 34%, 36%, 34% and 22%, respectively. Nausea, diarrhoea and vomiting were more common with survodutide than placebo.

These results are one reason the current development programme includes dedicated Phase 3 MASH trials as well as obesity studies.

What trials are still running?

The programme is broader than SYNCHRONIZE-1.

Zealand's current pipeline page lists Phase 3 obesity studies in people with and without type 2 diabetes, a cardiovascular outcomes trial, regional studies in Japan and China, and two Phase 3 MASH programmes called LIVERAGE and LIVERAGE-Cirrhosis ¹.

SYNCHRONIZE-2 is important because it studies people with type 2 diabetes, a group not included in SYNCHRONIZE-1. The cardiovascular programme matters because weight loss alone does not establish that a drug reduces heart attacks, strokes, kidney disease or mortality.

Those are separate clinical questions.

Is survodutide approved?

Survodutide is still described by its developers as investigational in September 2026 ¹.

The MHRA has published a paediatric investigation plan record for survodutide in obesity, with the invented name listed as "Not available at present" ⁸. A paediatric investigation plan is part of medicine development planning and should not be confused with a marketing authorisation.

The correct current description is therefore an investigational Phase 3 medicine with positive obesity efficacy data, not an established approved obesity medicine.

How should the Phase 3 result be interpreted?

SYNCHRONIZE-1 is meaningful evidence. It is a large randomised Phase 3 trial, it met its primary endpoints, and the result has now been published in a major peer reviewed journal.

It is also narrower than many online claims. The trial involved adults with obesity or overweight without type 2 diabetes. It compared survodutide with placebo, not directly with semaglutide, tirzepatide or retatrutide. It does not tell us which drug is best in a head to head comparison.

The strongest summary is simple: survodutide clearly produced greater weight loss than placebo in Phase 3, and the programme now has credible late stage human evidence. The exact headline percentage depends on the estimand being quoted, gastrointestinal side effects were common, and important questions about diabetes, cardiovascular outcomes, long term safety and regulatory approval are still being answered.

For a broader view of the current incretin field, see the BioRx comparison of semaglutide, tirzepatide and retatrutide.

Frequently asked questions

How much weight did people lose with survodutide in Phase 3?

In the published treatment regimen analysis, mean weight loss at 76 weeks was 12.2% with 3.6 mg and 13.0% with 6.0 mg, versus 5.4% with placebo Human ².

Why do some reports say 16.6%?

The 16.6% figure came from an efficacy estimand that estimates the effect assuming participants remained on treatment. The peer reviewed primary treatment regimen analysis, which incorporates treatment interruptions and other events, reported 13.0% at 6.0 mg.

Is survodutide a GLP-1 drug?

Partly. It activates both the GLP-1 receptor and the glucagon receptor. That makes it a dual agonist rather than a GLP-1 only medicine.

Has survodutide been compared directly with tirzepatide or semaglutide?

No head to head Phase 3 trial has established that comparison. Cross trial comparisons can be misleading because populations, estimands, treatment duration and trial rules differ.

Is survodutide available as an approved medicine?

Its developers still describe it as investigational. Positive Phase 3 data do not by themselves create a marketing authorisation.

References

Studies marked "View study in BioRx" sit in the clinical studies index with their design and evidence grade.

Survodutide Phase 3: What SYNCHRONIZE-1 Actually Found