SYNERGY-NASH: Tirzepatide and Fatty Liver Disease, and Why We Won't Print a Success Rate

What the trial did

SYNERGY-NASH randomised adults aged 18 to 80 with biopsy-confirmed MASH, stage F2 or F3 fibrosis, a BMI between 27 and 50 and a NAFLD activity score of 4 or above, with or without type 2 diabetes. Participants were assigned 1:1:1:1 to once-weekly subcutaneous tirzepatide at 5, 10 or 15 mg, or placebo, for 52 weeks, across 130 sites in ten countries. It was published in the New England Journal of Medicine in July 2024 and registered as NCT04166773.

The primary endpoint was MASH resolution without worsening of fibrosis on liver histology. That is a biopsy endpoint, which is considerably more demanding than the imaging surrogates most liver research relies on, and it is the main reason this trial carries weight despite being phase 2. A patient in this trial had a liver biopsy at baseline and another at 52 weeks — that is a substantial ask, and it produces a substantially harder result to dismiss.

Why we have not published a resolution percentage

Because the secondary sources disagree, and by a wide margin.

One reports resolution at 51.8%, 62.8% and 73.3% for the 5, 10 and 15 mg arms against 13.2% on placebo. Another reports 62% at 15 mg against 10% on placebo. Those cannot both describe the same arm of the same trial, and neither states which analysis produced its figure.

Publishing either would mean picking one at random and presenting it as settled. We have recorded both, flagged the conflict, and opened a task to read the NEJM full text and record the exact rate per arm with its estimand named. That is the same standard we apply to SURMOUNT-1's two estimands and to the orforglipron figures, and it is the reason this page is less quotable than the coverage elsewhere.

MASH resolution against fibrosis improvement

What can be said confidently is that tirzepatide was superior to placebo on a biopsy-confirmed histological endpoint, that the effect appeared dose-related, and that fibrosis improvement was less pronounced than MASH resolution at 52 weeks.

That last point matters more than it reads, and it is routinely lost in summaries. MASH resolution is inflammation settling. Fibrosis is scarring, and it is fibrosis stage that predicts progression to cirrhosis, liver failure and liver-related death. A drug that resolves inflammation without reversing established scarring is doing something valuable and incomplete.

Fifty-two weeks is also short for a fibrosis endpoint. Scar tissue does not remodel on the timescale inflammation resolves on, and a trial of this length may simply be too brief to show what a longer one would. That is an argument for the phase 3 programme rather than a criticism of this one.

What is not established

A phase 3 programme, SYNERGY-OUTCOMES, is reported to have launched in late 2025 targeting completion in 2032. Histological improvement at 52 weeks is not the same as fewer transplants or deaths, and the gap between those two things is where a great deal of hepatology research has previously foundered.

How it compares with semaglutide

No head-to-head trial has compared the two for liver endpoints. Semaglutide's phase 2 MASH work reported resolution around 59% against 17% on placebo, but different trials with different populations, biopsy criteria and durations are not comparable in the way a head-to-head would be.

Anyone presenting one molecule as superior for liver disease is comparing across trials, which is the same error that made SURMOUNT-5 necessary for the weight question. Until a head-to-head exists, the honest position is that both have signal and neither has been shown better.

What a patient with fatty liver disease should take from this

That this is a real and reasonably strong signal on a demanding endpoint, in a condition with few options — and that it is phase 2 evidence for an unapproved indication.

If you have MASH and obesity, this is worth raising with a hepatologist rather than with a weight-management platform. The biopsy staging that determines whether the trial population resembles you is not something an intake questionnaire establishes, and F2–F3 fibrosis is a specific clinical picture rather than a general description of fatty liver.

It is also worth knowing that liver disease is one of the conditions weight drives, which means the benefit may run substantially through weight reduction rather than through anything liver-specific. That does not make it less useful. It does mean the choice between agents may come down to which one you tolerate and can sustain, rather than to a liver-specific property one of them has.

How to check any claim on this page for yourself

Everything above should be checkable, and most of it is. Trial claims resolve to a registry entry and a peer-reviewed publication; regulatory claims resolve to an agency document; pricing claims resolve to a provider’s own published page read on a stated date.

Where we could not verify something, we say so rather than rounding it into confidence. Every pharmacy relationship on this site carries a reported rather than verified label, because not one provider has named its fulfilling pharmacy and registration class to us. That is the field we would weight most heavily if we had it, and it is the question worth putting first if you can only ask one — because the FDA has proposed excluding tirzepatide from the 503B bulks list, and whether your supply runs through a 503B outsourcing facility or a 503A pharmacy determines your exposure to that decision.

Four checks take about ten minutes between them. Confirm your prescriber holds a current licence in your state, through that state’s medical board rather than through the provider’s own page. Confirm the fulfilling pharmacy is licensed, and registered as a nonresident pharmacy in your state if it ships from elsewhere. Search the pharmacy’s name against FDA warning letters and recall notices, both public. And ask for a certificate of analysis matched to the batch number on your vial.

None of that establishes that the medicine in your hand is safe. It establishes that the parties involved are inside the regulatory system and currently authorised, which is a floor rather than a guarantee. The honest framing is that you are reducing risk rather than eliminating it — and a provider unwilling to give you the names needed to run those checks has told you something worth knowing.