In a 52‑week trial, people with fatty liver disease (MASH) who took tirzepatide lost a lot of weight, lowered their blood sugar, and reduced liver fat, which was linked to real improvements in liver health. The bigger the weight loss and the better the blood sugar control, the more likely the liver disease got better.

To explore the relationship between metabolic and histological responses in a phase 2 trial of tirzepatide in metabolic dysfunction-associated steatohepatitis (MASH). This is a participant-level post hoc analysis of the 52-week, double-blind, randomized, placebo-controlled SYNERGY-NASH trial (NCT04166773). Participants (n = 190) with MASH and stage 2/3 fibrosis were randomly assigned to receive tirzepatide (5, 10, or 15 mg) or placebo once weekly. The primary end point was MASH resolution without worsening of fibrosis. Secondary end points included fibrosis improvement by at least one stage without worsening of MASH. Metabolic changes were evaluated in responders and nonresponders for histological end points in 154 participants who completed the study on treatment. At baseline, 59% had type 2 diabetes and mean BMI was 35.7 kg/m2. Compared with nonresponders, greater body weight reductions were observed in responders for MASH resolution (-16.0% vs. -7.0%; P < 0.001) and for fibrosis improvement (-13.6% vs. -9.8%; P = 0.023). Reductions in HbA1c were greater for MASH responders (-1.2% vs. -0.6%; P < 0.001) and fibrosis responders (-1.2% vs. -0.7%; P = 0.004) than for nonresponders. Compared with nonresponders, greater improvements in liver fat and measures of adipose tissue insulin sensitivity (adipose tissue insulin resistance index and adiponectin) were observed with MASH responders (P < 0.001). In causal mediation analyses, normalization of liver fat was a significant mediator of both MASH resolution and fibrosis improvement. In this post hoc exploratory analysis, MASH resolution and fibrosis improvement were associated with body weight reduction, improved glycemic control, and normalization of liver fat. Weight reduction and metabolic improvements with tirzepatide treatment potentially contributed to disease modification in MASH.