MASH is the silent progression from fatty liver to inflammation, fibrosis, and cirrhosis.

MASH begins with insulin resistance. When skeletal muscle and adipose tissue stop responding normally to insulin, the body compensates with hyperinsulinemia. Adipose tissue releases free fatty acids at an increased rate, and the liver — which is already producing glucose inappropriately — receives a flood of substrate it cannot fully metabolize. At the same time, the liver increases its own de novo lipogenesis (fat synthesis from carbohydrates), driven by the insulin-activated transcription factor SREBP-1c. The result is hepatic steatosis: lipid accumulates in hepatocytes as large fat droplets that displace the nucleus to the cell periphery.

Fat alone does not cause disease — the majority of people with simple steatosis never develop complications. What converts steatosis to MASH is lipotoxicity and inflammation. Excess free fatty acids and their oxidized metabolites (diacylglycerols, ceramides, lysophosphatidylcholine) are directly toxic to hepatocytes. They trigger mitochondrial dysfunction, endoplasmic reticulum stress, and the production of reactive oxygen species. Injured hepatocytes release danger signals that activate Kupffer cells (the liver's resident macrophages) and recruit additional immune cells. The result is lobular inflammation, and hepatocyte injury manifests as ballooning — swollen, pale, injured hepatocytes visible on biopsy.

The final step is fibrosis. Persistent inflammation activates hepatic stellate cells, which transform into myofibroblasts and deposit collagen in the perisinusoidal space (zone 3) and around portal tracts. Initially this is a normal wound-healing response, but with ongoing injury the fibrosis becomes progressive and can bridge between portal tracts — producing the architectural distortion that eventually leads to cirrhosis. Once cirrhosis develops, the risks of decompensation (ascites, encephalopathy, variceal bleeding) and hepatocellular carcinoma become substantial. Fibrosis stage, not inflammation grade, is the single strongest predictor of long-term outcome.

The metabolic context matters — MASH rarely occurs in isolation. It is usually accompanied by obesity, type 2 diabetes, dyslipidemia, and hypertension — the same cluster that defines metabolic syndrome. This overlap is why treatments for one condition often affect the other. GLP-1 receptor agonists, developed for diabetes and obesity, have shown benefit in MASH. Managing the metabolic context is part of managing the liver. A reference like this one on metformin for diabetes illustrates how the same metabolic pathways are targeted across related conditions.

Resmetirom is the first approved MASH-specific medication and lists at approximately $47,000 per year — expensive, but covered by many commercial plans with prior authorization, and subject to manufacturer copay assistance for eligible patients. Medicare Part D coverage varies, but the 2025 Part D redesign caps annual out-of-pocket costs at $2,000. Foundation grants (HealthWell, PAN Foundation) may help. Not all patients will qualify — the FDA label restricts use to F2–F3 MASH, and prior authorization typically requires confirmation of fibrosis stage by non-invasive testing or biopsy.

GLP-1 receptor agonists — while not formally FDA-approved for MASH — are frequently used off-label and are covered by most plans for obesity or diabetes, which many MASH patients also have. This overlapping coverage has made them more accessible than resmetirom for many patients, despite the absence of a MASH-specific indication. For patients paying out of pocket for other chronic medications — including for diabetes, hypertension, and dyslipidemia, which commonly coexist with MASH — pharmacy-level pricing still matters. A live comparison across licensed U.S. sellers, like the one for generic Metformin cost, illustrates the same pricing dynamics that apply to any generic medication.

Bariatric surgery is covered by most commercial plans and Medicare when medically indicated for patients with BMI ≥ 35 and comorbidities including MASH. This is often the most cost-effective long-term intervention for patients who meet criteria, because it addresses obesity, diabetes, hypertension, and MASH simultaneously. Not all patients meet criteria, and access depends on local surgical programs and insurance approval.

For patients on multiple chronic medications — which is the rule rather than the exception in MASH — it is worth keeping pharmacy-level pricing in mind. The same generic drug can cost meaningfully more at one licensed pharmacy than another, and a short comparison before each refill is a useful habit. A resource like this on trusted pharmacy comparison is a starting point.