TLDR
Retatrutide has produced unusually large reductions in liver fat in a peer-reviewed randomized Phase 2a substudy involving people with obesity or overweight and metabolic dysfunction-associated steatotic liver disease, or MASLD.
Among 98 participants with at least 10% liver fat by MRI-PDFF, average relative liver-fat reductions after 24 weeks were 42.9%, 57.0%, 81.4%, and 82.4% with 1, 4, 8, and 12 mg retatrutide, compared with a 0.3% increase with placebo. At the two highest doses, 79% and 86% of participants reached liver-fat levels below 5% at week 24.
Those are large imaging effects, but they do not prove that retatrutide reverses liver fibrosis, prevents cirrhosis, or resolves MASH. The study did not use paired liver biopsies to establish those outcomes. Some exploratory fibrosis and liver-injury biomarkers improved, while ALT, AST, FIB-4, and ELF did not show consistent differences from placebo.
Lilly has now moved retatrutide into a much larger Phase 3 liver-outcomes program. SYNERGY-Outcomes plans to enroll about 4,500 adults with high-risk MASLD and asks a much harder question: whether retatrutide or tirzepatide can actually prevent major liver outcomes such as cirrhosis, ascites, variceal bleeding, hepatic encephalopathy, liver transplantation, and death.
What Is MASLD?
MASLD stands for metabolic dysfunction-associated steatotic liver disease.
It is the newer name for the condition previously called nonalcoholic fatty liver disease, or NAFLD.
Under the current nomenclature, MASLD refers to hepatic steatosis occurring in the presence of at least one cardiometabolic risk factor and without another predominant explanation for the steatosis.
The disease spectrum can range from relatively uncomplicated fat accumulation to:
steatohepatitis,
fibrosis,
cirrhosis,
and liver cancer.
The inflammatory form previously called NASH is now called MASH, or metabolic dysfunction-associated steatohepatitis. MASH includes hepatocellular injury and inflammation rather than fat accumulation alone.
That distinction is critical when interpreting retatrutide research.
Reducing liver fat is important.
It is not identical to proving that advanced liver disease has been reversed.
Liver Fat Is Only One Part of MASLD
MASLD often begins with accumulation of excess triglyceride within hepatocytes.
But the amount of fat visible in the liver does not fully determine long-term clinical risk.
The more consequential progression involves:
inflammation,
hepatocyte injury,
fibrosis,
and eventually cirrhosis.
Current European clinical guidelines emphasize fibrosis assessment because the stage of fibrosis is much more closely associated with liver-related outcomes than simple presence of steatosis alone.
So when a trial reports an 80% reduction in liver fat, the result is impressive.
But the right next question is:
What happened to the actual liver disease?
Why Might Retatrutide Affect Liver Fat?
Retatrutide activates:
GIP receptors,
GLP-1 receptors,
and glucagon receptors.
Each pathway can influence metabolism.
GLP-1 and GIP receptor activity can influence food intake, glucose regulation, insulin signaling, and body weight.
Glucagon receptor biology is particularly interesting in the liver.
The glucagon receptor is expressed strongly in hepatocytes and influences:
hepatic glucose production,
fat oxidation,
amino-acid metabolism,
and other components of hepatic energy metabolism.
The original retatrutide program found that glucagon-receptor activation contributed to increased energy expenditure in mice while GIP and GLP-1 receptor activity reduced calorie intake.
That makes liver effects biologically plausible.
But the clinical trial cannot tell us that glucagon receptor activation alone caused the decrease in liver fat.
Retatrutide also causes very large reductions in body weight and visceral adipose tissue, which can independently improve MASLD.
The Liver-Fat Study Was a Substudy of the Phase 2 Obesity Trial
The main Phase 2 obesity trial enrolled 338 adults.
Of those, 98 participants had liver fat of at least 10% by magnetic resonance imaging proton density fat fraction, or MRI-PDFF, and entered the MASLD substudy.
They were randomized to:
| Treatment | Participants |
|---|---|
| Placebo | 19 |
| Retatrutide 1 mg | 20 |
| Retatrutide 4 mg | 19 |
| Retatrutide 8 mg | 22 |
| Retatrutide 12 mg | 18 |
Treatment continued for 48 weeks.
The primary liver endpoint was relative change in liver fat at week 24.
This was not a large liver-disease outcomes trial.
It was a relatively small imaging substudy designed to determine whether the strong metabolic and weight effects observed in the obesity trial were accompanied by measurable changes in hepatic fat.
What Is MRI-PDFF?
MRI-PDFF stands for magnetic resonance imaging proton density fat fraction.
It is a noninvasive imaging technique used to estimate the fraction of liver tissue signal attributable to fat.
Unlike a routine ultrasound that may simply report whether steatosis appears present, MRI-PDFF can quantify liver fat across the organ with relatively high precision.
That makes it useful in early-stage clinical trials.
A participant might begin with a liver-fat fraction of 20% and later measure 10%.
That can be reported in two ways.
The absolute reduction is 10 percentage points.
The relative reduction is 50%.
The retatrutide study primarily emphasized relative percentage change.
That distinction matters when reading the headline numbers.
Retatrutide Reduced Liver Fat by More Than 80% at Higher Doses
At week 24, mean relative changes from baseline were:
| Treatment | Relative Liver-Fat Change |
|---|---|
| Retatrutide 1 mg | -42.9% |
| Retatrutide 4 mg | -57.0% |
| Retatrutide 8 mg | -81.4% |
| Retatrutide 12 mg | -82.4% |
| Placebo | +0.3% |
Every retatrutide dose was statistically superior to placebo for the primary endpoint.
The effect at 8 and 12 mg was especially large.
By 24 weeks, most of the measurable liver-fat reduction at the higher doses had already occurred.
This differed from total body weight, which continued falling more substantially beyond week 24.
Many Participants Reached Liver-Fat Levels Below 5%
Researchers also examined how many participants reached less than 5% liver fat.
At 24 weeks:
27% of the 1 mg group,
52% of the 4 mg group,
79% of the 8 mg group,
86% of the 12 mg group,
and 0% of the placebo group
reached that threshold.
At first glance, it is tempting to describe this as “reversing fatty liver.”
The paper itself refers to resolution of steatosis when liver fat fell below the specified threshold.
But the broader clinical interpretation still needs caution.
A person can have little measurable liver fat and still have residual fibrosis.
Fat content and fibrotic scar are different biological properties.
The Week 48 Results Looked Even Stronger, but the Sample Was Much Smaller
At week 48, relative liver-fat changes were reported as:
1 mg: -51.3%
4 mg: -59.0%
8 mg: -81.7%
12 mg: -86.0%
placebo: -4.6%.
But there is an important limitation.
Far fewer participants had usable week-48 MRI data.
Only about 44% of the original substudy population had week-48 liver-fat measurements available, partly because of treatment discontinuation and imaging visits falling outside the required window. The individual treatment groups had only about eight or nine participants with those measurements.
For that reason, the 24-week endpoint is the more robust liver-fat result.
The week-48 findings are supportive but less precise.
Liver Fat Fell Much Faster Than Body Fat
One of the most interesting findings was the timing.
Liver fat fell rapidly during the first 24 weeks.
Meanwhile, body weight, visceral fat, and subcutaneous abdominal fat continued to decline through week 48.
The investigators described this as a possible floor effect.
There is only so much excess fat in the liver to remove. Once hepatic fat approaches normal levels, additional weight loss cannot keep producing the same relative reduction indefinitely.
The study estimated that near-maximal liver-fat reduction occurred around 20% body-weight reduction.
This suggests the liver may lose excess fat earlier than other major adipose depots during substantial weight reduction.
The Relationship With Weight Loss Was Very Strong
At week 24, relative liver-fat reduction correlated strongly with percentage body-weight change.
The reported correlation coefficient was approximately:
r = 0.800.
At week 48 it remained strong at:
r = 0.739.
A correlation of 1 would represent a perfect positive relationship.
So values around 0.8 indicate a substantial association.
Liver-fat reduction also correlated with changes in waist circumference and both visceral and abdominal subcutaneous adipose tissue.
That makes an important mechanistic point.
The study does not show that retatrutide’s liver effects are independent of its weight-loss effects.
In fact, the two were closely connected.
Visceral Fat Fell Substantially
Visceral adipose tissue, or VAT, is the fat stored around internal abdominal organs.
It is particularly relevant to cardiometabolic disease.
By week 48, retatrutide produced visceral-fat reductions ranging from about 16% to 48%, depending on dose, compared with a slight increase in placebo.
Abdominal subcutaneous fat also fell substantially, reaching reductions of more than 40% in some higher-dose groups.
Liver-fat change was strongly correlated with changes in both adipose compartments.
This reinforces the idea that the liver findings belong to a broader change in metabolic fat distribution rather than being an isolated hepatic phenomenon.
Several Metabolic Biomarkers Improved
Researchers also measured metabolic markers.
At doses of 4 mg or greater, retatrutide increased adiponectin and reduced leptin under several study conditions.
Triglycerides decreased significantly at 4 mg or greater.
Measures of insulin resistance and related metabolic biomarkers also moved in directions consistent with improved insulin sensitivity.
Beta-hydroxybutyrate increased under some conditions.
That finding is interesting because ketone production is associated with hepatic fatty-acid oxidation and could fit with a glucagon-related shift in liver metabolism.
But again, biomarker changes are mechanistic clues.
They do not establish the long-term clinical outcome by themselves.
What Happened to Markers of Liver Injury?
The study also examined biomarkers related to MASH and fibrosis.
One was K-18, or cytokeratin-18.
Fragments of K-18 can be associated with hepatocyte injury and cell death.
K-18 fell significantly compared with placebo with retatrutide 8 mg at week 24 and with 8 and 12 mg at week 48.
That suggests the liver changes may extend beyond simple fat reduction.
But K-18 is still a biomarker.
It is not a liver biopsy.
What Happened to Pro-C3?
Researchers also measured Pro-C3, a marker associated with formation of type III collagen and extracellular matrix remodeling.
Fibrosis involves abnormal deposition of collagen and other matrix material, so Pro-C3 is studied as a potential noninvasive fibrosis-related biomarker.
Pro-C3 decreased significantly with retatrutide doses of 4 mg or greater at week 24.
At week 48, significant decreases were reported with the 1, 4, and 8 mg groups.
Interestingly, the pattern was not a clean dose-response relationship.
The 12 mg group did not show a statistically significant week-48 Pro-C3 difference in the same way.
That is one reason the biomarker evidence should not be oversimplified into:
“Retatrutide reversed fibrosis.”
The study does not establish that.
Several Other Liver Markers Did Not Consistently Improve
This is one of the most important details in the entire paper.
Mean:
ALT,
AST,
FIB-4,
and ELF
did not change consistently versus placebo.
FIB-4 and ELF are among the tools used to evaluate fibrosis risk.
Current MASLD guidelines recommend focusing heavily on fibrosis assessment because fibrosis is more closely tied to meaningful liver-related outcomes.
So the imaging evidence for liver-fat reduction is very strong.
The fibrosis evidence from this study is much less definitive.
Was Liver Biopsy Used?
No paired liver-biopsy program was used to establish histological MASH resolution or fibrosis regression in this substudy.
That limits what the study can prove.
A biopsy can evaluate:
steatosis,
lobular inflammation,
hepatocyte ballooning,
and fibrosis stage.
MRI-PDFF is excellent at quantifying fat.
It cannot directly tell researchers whether fibrotic scar tissue has disappeared.
This is the central distinction readers need to understand.
Does an 80% Liver-Fat Reduction Matter Anyway?
Yes.
Liver-fat reduction is biologically meaningful and is associated with histological response in other MASH trials.
A multicenter study found that patients achieving at least a 30% relative reduction in MRI-PDFF had substantially higher odds of histological response than those who did not reach that threshold.
A subsequent meta-analysis across seven studies and 346 participants found that people with a ≥30% MRI-PDFF reduction were much more likely to show histological response and NASH resolution.
Retatrutide’s 8 and 12 mg groups exceeded that imaging threshold by a very wide margin on average.
That makes the result scientifically interesting.
But an association between MRI improvement and histology in other studies is not the same as directly demonstrating retatrutide-induced histological improvement.
The latter requires retatrutide-specific evidence.
Why Fibrosis Matters More Than Fat Alone
The liver can tolerate substantial fat accumulation for some time without developing advanced disease.
The major long-term concern is progression to fibrosis and cirrhosis.
Advanced fibrosis can eventually lead to:
portal hypertension,
ascites,
esophageal or gastric varices,
hepatic encephalopathy,
liver failure,
hepatocellular carcinoma,
and liver transplantation.
Current MASLD clinical guidance therefore places significant emphasis on identifying fibrosis rather than only diagnosing steatosis.
A treatment that removes liver fat but does not reduce progression to these outcomes would be less clinically important than one that actually prevents advanced liver disease.
Could Retatrutide Have Direct Liver Effects Beyond Weight Loss?
Possibly.
The glucagon receptor gives retatrutide an unusual hepatic mechanism compared with pure GLP-1 receptor agonists.
Glucagon signaling can alter:
fatty-acid oxidation,
ketogenesis,
hepatic substrate handling,
and amino-acid metabolism.
That provides a plausible pathway for a direct liver effect.
The retatrutide study’s changes in beta-hydroxybutyrate, triglycerides, insulin sensitivity, and other metabolic markers are consistent with a broad change in energy metabolism.
But the trial was not designed to isolate glucagon’s contribution.
To prove a direct, weight-independent effect, researchers would need a design capable of separating changes produced by weight loss from changes produced by receptor pharmacology.
The current data cannot do that cleanly.
The Trial Was Small
Another limitation is sample size.
The entire MASLD substudy contained only 98 participants.
The dose groups contained between 18 and 22 participants each.
And week-48 imaging data were available for substantially fewer.
That is enough to detect the very large MRI-PDFF effect.
It is nowhere near enough to evaluate uncommon liver events or long-term disease progression.
The study should therefore be viewed as a strong proof-of-concept metabolic liver study, not a definitive liver-outcomes trial.
The Research Has Now Moved to Actual Liver Outcomes
This is where the retatrutide program becomes much more interesting.
Lilly is currently running SYNERGY-Outcomes, a large Phase 3 master-protocol study in adults with high-risk MASLD.
The trial plans to enroll approximately 4,500 participants.
Participants are randomized within the program to retatrutide, tirzepatide, or placebo.
Rather than asking only how much liver fat disappears, the primary endpoint evaluates major adverse liver outcomes.
SYNERGY-Outcomes Is Asking the Question That Actually Matters
The composite endpoint includes events such as:
progression to cirrhosis,
large esophageal or gastric varices,
ascites,
hepatic encephalopathy,
variceal bleeding,
a significant increase in MELD score,
liver transplantation,
and all-cause mortality.
That is a major shift in evidence level.
The Phase 2 study asked:
Does retatrutide remove fat from the liver?
SYNERGY-Outcomes asks:
Does treatment prevent people from developing serious liver disease?
Those are very different questions.
The latter is ultimately much more important.
The Phase 3 Liver Trial Will Take Years
ClinicalTrials.gov lists SYNERGY-Outcomes as recruiting, with approximately 224 weeks of primary follow-up and an overall study timeline extending into the early 2030s.
That long duration reflects the nature of MASLD.
Changes in MRI-PDFF can occur within months.
Progression to cirrhosis, liver failure, or transplantation may take years.
You cannot replace a long clinical-outcomes trial simply by measuring a rapidly changing biomarker.
What the Retatrutide Liver Research Supports Today
The evidence is strong that retatrutide can dramatically reduce liver fat in people with obesity-associated MASLD.
The magnitude at 8 and 12 mg was large enough that most participants with available week-24 imaging reached liver-fat levels below 5%.
The changes were closely connected with:
body-weight loss,
visceral-fat reduction,
improved insulin sensitivity,
and changes in lipid metabolism.
There are also suggestive changes in selected MASH and fibrosis-related biomarkers.
But the evidence does not yet establish that retatrutide:
reverses established fibrosis,
prevents cirrhosis,
reduces liver cancer,
prevents liver failure,
or improves survival from liver disease.
Those questions are now being studied directly.
Why This May Become One of the Most Important Retatrutide Research Areas
Weight loss is the result receiving most of the attention around retatrutide.
The liver program may eventually be more scientifically important.
MASLD is tightly connected with obesity, insulin resistance, type 2 diabetes, dyslipidemia, and cardiovascular disease.
A single peptide that could substantially change:
body weight,
glycemic control,
visceral fat,
liver fat,
and ultimately liver outcomes
would represent a much broader metabolic intervention than a drug judged only by pounds lost.
The imaging data suggest that possibility.
The Phase 3 outcomes trial will determine whether it translates into meaningful protection against advanced liver disease.
That distinction is exactly where the evidence stands today.
FAQs
How much did retatrutide reduce liver fat?
At week 24, average relative liver-fat reductions were 42.9%, 57.0%, 81.4%, and 82.4% with 1, 4, 8, and 12 mg retatrutide, respectively, compared with a 0.3% increase with placebo.
Did retatrutide eliminate fatty liver?
At week 24, 79% of the 8 mg group and 86% of the 12 mg group reached MRI-PDFF liver-fat levels below 5%. That represents resolution of steatosis by the study’s imaging definition, but it does not prove that fibrosis or MASH was eliminated.
Did retatrutide reverse liver fibrosis?
That has not been established. The Phase 2a substudy did not use paired liver biopsies to demonstrate fibrosis regression.
Did liver enzymes improve?
Some liver-related biomarkers changed, but ALT, AST, FIB-4, and ELF did not show consistent improvements versus placebo.
Was liver-fat reduction related to weight loss?
Yes. The relationship was strong, with a correlation of approximately 0.80 between relative liver-fat reduction and weight change at week 24.
Is retatrutide being studied in a larger MASLD trial?
Yes. SYNERGY-Outcomes plans to enroll about 4,500 adults with high-risk MASLD and evaluate whether retatrutide and tirzepatide can prevent major adverse liver outcomes.
Is retatrutide approved for MASLD?
No. Retatrutide remains investigational.
References
Sanyal AJ, Kaplan LM, Frias JP, et al. Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial. Nature Medicine. 2024;30:2037-2048. Read the full Nature Medicine study
European Association for the Study of the Liver, European Association for the Study of Diabetes, and European Association for the Study of Obesity. Clinical Practice Guidelines on the Management of Metabolic Dysfunction-Associated Steatotic Liver Disease. 2024. Read the MASLD clinical guidelines
Jayakumar S, Middleton MS, Lawitz EJ, et al. Multicenter Validation of Association Between Decline in MRI-PDFF and Histologic Response in NASH. Hepatology. Read the MRI-PDFF validation study
Stine JG, et al. Change in MRI-PDFF and Histologic Response in Patients With Nonalcoholic Steatohepatitis: A Systematic Review and Meta-Analysis. Clinical Gastroenterology and Hepatology. Read the systematic review and meta-analysis
ClinicalTrials.gov. SYNERGY-Outcomes: A Master Protocol of Multiple Agents in Adults With High-Risk MASLD. NCT07165028. View the Phase 3 liver-outcomes study
Coskun T, Urva S, Roell WC, et al. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss. Cell Metabolism. 2022. Read the original retatrutide mechanism paper