Rezdiffra (Resmetirom) for NASH F2, F3: What Clinicians Actually Do

What Resmetirom Is and Why It Matters for Women

Resmetirom received FDA approval on March 14, 2024 as the first and only pharmacotherapy approved specifically for MASH with liver fibrosis stages F2 and F3. This is not an off-label use. The drug's brand name is Rezdiffra, and it is made by Madrigal Pharmaceuticals.

MASH (metabolic-associated steatohepatitis, formerly called NASH) affects an estimated 1.5 to 6.45 million Americans with fibrosis stage F2 or higher, and women are not a minority in that group. Female sex actually changes the disease trajectory at nearly every life stage, which is why understanding resmetirom through a women's-health lens matters clinically.

How the Drug Works

Resmetirom selectively activates thyroid hormone receptor-beta (THR-β), the predominant receptor isoform in the liver. THR-β activation in hepatocytes increases fatty acid oxidation, reduces lipid synthesis, and improves mitochondrial function. Because it targets THR-β rather than THR-α (the cardiac and bone isoform), it aims to produce the liver benefits of thyroid hormone without causing atrial fibrillation or bone loss. The FDA label specifies that resmetirom does not meaningfully suppress TSH at therapeutic doses, a point that matters when you are managing a woman with co-existing hypothyroidism.

Why Women Are a Priority Population

Women with PCOS have a prevalence of NAFLD/MASH estimated between 32% and 55%, driven by insulin resistance, hyperandrogenism, and often elevated ALT that gets dismissed as non-specific. Postmenopausal women lose the partial hepatoprotection that estrogen provides against hepatic de novo lipogenesis, which accelerates fibrosis progression after menopause. Women have also been under-represented in MASH trials historically, and MAESTRO-NASH is no exception in that regard (see the evidence-gap section below).

How Clinicians Are Actually Using Resmetirom

The approved indication is MASH with fibrosis stage F2 or F3 confirmed on liver biopsy or an accepted non-invasive test. That phrase "what clinicians actually do" reflects real-world tension between the biopsy requirement and how most patients are diagnosed in practice.

The Biopsy vs. Non-Invasive Testing Problem

The FDA label requires confirmed MASH with fibrosis, but many hepatologists and gastroenterologists are moving toward non-invasive fibrosis assessment before recommending a biopsy. In practice, a combination of FIB-4 index, vibration-controlled transient elastography (VCTE), and MRI-PDFF is used to estimate fibrosis stage. Clinicians prescribing resmetirom without a biopsy are technically acting within a gray zone that a reasonable-standard-of-care argument could support, but the FDA label does not endorse this path explicitly.

Expect your prescriber to want at least one of: liver biopsy, FibroScan showing stiffness consistent with F2, F3, or AGILE score consistent with significant fibrosis before they write the script.

Dosing in Clinical Practice

The approved doses are:

• 80 mg once daily for patients with BMI <35 kg/m²
• 100 mg once daily for patients with BMI ≥35 kg/m²

Both doses are taken with food to reduce nausea. No titration period is required, though some clinicians start at 80 mg regardless of BMI for the first four weeks in patients who report GI sensitivity, then increase. This lower-start approach is not in the label but reflects practical caution.

Combination With GLP-1 Receptor Agonists

Resmetirom is increasingly used alongside semaglutide or tirzepatide in women who have both MASH and obesity or type 2 diabetes. The MAESTRO-NASH trial excluded patients on GLP-1 agonists, so combination data are from small observational series only. Clinicians are doing it. The pharmacokinetic interaction is not well-characterized in women specifically, and you should be aware that the combination may enhance GI side effects in the first month.

MAESTRO-NASH: What the Trial Actually Showed

MAESTRO-NASH was the Phase 3 registration trial that supported FDA approval. Published in the New England Journal of Medicine in 2024, it randomized 966 patients with biopsy-confirmed MASH and fibrosis stage F1B, F2, or F3 to resmetirom 80 mg, resmetirom 100 mg, or placebo.

Primary Endpoints

The trial used two co-primary histological endpoints at 52 weeks:

1. MASH resolution (no steatohepatitis) with no worsening of fibrosis
2. Fibrosis improvement by at least one stage with no worsening of MASH activity

Results at 52 weeks:

| Endpoint | 80 mg | 100 mg | Placebo | |---|---|---|---| | MASH resolution | 25.9% | 29.9% | 9.7% | | ≥1-stage fibrosis improvement | 24.2% | 25.9% | 14.2% |

Both doses beat placebo on both endpoints with statistical significance (p <0.001 for all comparisons). These are the numbers that got the drug approved.

What the Trial Did Not Tell Us About Women

Women made up approximately 53% of MAESTRO-NASH participants, which is better than historical MASH trials. But the published data did not report sex-stratified efficacy, meaning we do not know whether the 25 to 30% MASH resolution rate held equally for women across life stages, whether postmenopausal women responded differently from premenopausal women, or whether women with PCOS had different response curves. This absence of sex-stratified reporting is a meaningful evidence gap. Any clinician claiming equal efficacy across female life stages is extrapolating from aggregate data, not from female-specific trial data.

Women-Specific Physiology and Resmetirom: What Changes by Life Stage

Reproductive Years (Ages 18 to 40)

During the reproductive years, estrogen's partial hepatoprotection means many women with early MASH may not yet have reached F2, F3 fibrosis. PCOS is the major exception: insulin resistance in PCOS accelerates fibrosis independent of menstrual estrogen levels. A 2019 meta-analysis found that women with PCOS had an odds ratio of 3.93 for NAFLD compared with controls without PCOS. If you have PCOS and elevated liver enzymes or a high FIB-4, MASH staging is warranted before attributing the enzyme elevation to the syndrome alone.

Resmetirom requires reliable contraception in reproductive-age women (see the pregnancy section below). This is a prescribing barrier that clinicians must address before starting treatment.

Perimenopause (Typically Ages 45 to 55)

Estrogen loss in perimenopause removes a degree of protection against hepatic de novo lipogenesis and shifts fat distribution toward visceral accumulation. Women who had mild MASH (F1) in their 40s may progress to F2, F3 in the early perimenopause years without dramatic weight gain. A 2023 review in Hepatology noted that post-menopausal women have a 2-fold higher rate of advanced fibrosis compared with pre-menopausal women with equivalent metabolic profiles. If you are in perimenopause and have had MASH diagnosed for several years, asking for a repeat fibrosis assessment is clinically appropriate.

The TSH monitoring requirement for resmetirom matters especially here. Subclinical hypothyroidism is common in perimenopause, and THR-β agonism could theoretically shift thyroid axis feedback. The MAESTRO-NASH trial showed mean TSH decreased by 0.25 to 0.40 mIU/L from baseline on active treatment, which remained within the normal range for most participants. Your prescriber should check TSH at baseline and at three months, especially if you are on levothyroxine.

Post-Menopause

Post-menopause, the combination of visceral fat redistribution, insulin resistance, and dyslipidemia creates a high-risk metabolic environment for MASH progression. Resmetirom's lipid effects are notable: in MAESTRO-NASH, LDL-C was reduced by approximately 16 to 19% and triglycerides by 23 to 31% from baseline at 24 weeks. For post-menopausal women managing cardiovascular risk alongside MASH, these lipid benefits represent a secondary gain that clinicians explicitly weigh when choosing resmetirom over watchful waiting.

Female-Relevant Conditions This Drug Touches

PCOS and Insulin Resistance

Resmetirom does not treat PCOS directly, and it does not lower androgens. Its benefit in PCOS-driven MASH is limited to the hepatic pathway. If hyperandrogenism and anovulation are active concerns, those require separate management. Resmetirom should be seen as a liver-specific tool, not a metabolic cure for PCOS.

Thyroid Disease

Women are five to eight times more likely than men to have autoimmune thyroid disease. The FDA prescribing information for Rezdiffra states the drug is contraindicated in patients with decompensated liver disease and should be used with caution in patients on thyroid hormone replacement. In practice, if you are on stable levothyroxine, your prescriber will want a TSH level before starting and likely again at 8 to 12 weeks. Dose adjustments to your levothyroxine may be needed.

Cardiovascular Risk

MASH and cardiovascular disease share metabolic roots, and cardiovascular events remain the leading cause of death in MASH patients. The MAESTRO-NASH trial showed no increase in major adverse cardiovascular events on resmetirom, and the LDL and triglyceride reductions may carry a cardiovascular benefit, though no outcomes trial has confirmed this in women.

Pregnancy, Lactation, and Contraception: Required Reading

Resmetirom is contraindicated in pregnancy. This is not a soft caution. The drug caused embryo-fetal toxicity in animal reproduction studies. The FDA label carries a Contraindication in pregnancy and a Boxed Warning-level caution regarding fetal risk.

What "Contraindicated in Pregnancy" Means in Practice

If you could become pregnant, your prescriber is required to confirm that you are using effective contraception before starting resmetirom and throughout the course of treatment. The label does not specify a washout period after stopping before conception is considered safe, but given the drug's half-life of approximately 6 hours (terminal phase longer due to active metabolites), most clinicians recommend waiting at least one full menstrual cycle after discontinuation before attempting conception. This is a clinician-level extrapolation, not a label-specified interval.

Human data in pregnancy are absent. All embryo-fetal toxicity data come from animal models.

Lactation

The FDA label states that the presence of resmetirom in human breast milk is unknown. Animal studies showed drug-related effects in nursing offspring. The label advises against breastfeeding during treatment and for a period after the last dose. The specific duration is not stated, but a minimum of five half-lives (approximately 3 to 4 days for the parent compound) is standard pharmacokinetic practice. Given MASH is generally a longer-term condition, if you are breastfeeding a newborn, resmetirom initiation is typically deferred until breastfeeding is complete.

Contraception Requirements

Any woman of reproductive potential starting resmetirom should use contraception throughout treatment. Your prescriber may ask you to document your contraceptive method before the prescription is filled. Options that do not interact significantly with resmetirom include:

• Combined oral contraceptives (no known PK interaction reported in the label, though formal interaction studies in women are limited)
• IUD (hormonal or copper)
• Barrier methods
• Permanent contraception

There is no REMS program as of the date of this article's publication, so prescriptions are not gated through a mandatory enrollment system, but the contraception conversation is a clinical and ethical standard of care.

Side Effects Women Should Know About

The most common adverse effects from MAESTRO-NASH were gastrointestinal:

• Nausea: approximately 27% (80 mg) and 30% (100 mg) vs. 12% placebo
• Diarrhea: approximately 28% (80 mg) and 29% (100 mg) vs. 16% placebo
• Vomiting: approximately 9 to 11% vs. 4% placebo

Most GI events were mild-to-moderate and occurred in the first four to eight weeks of treatment. Women in MAESTRO-NASH did not have sex-stratified adverse event reporting published, but GI side effects are generally more common in women than men with GLP-1 agonists, and it is reasonable to anticipate a similar pattern with resmetirom, though this is extrapolation.

Gallbladder effects are a notable concern. Thyroid hormone receptor agonism can affect bile composition. The label notes an increase in cholelithiasis in MAESTRO-NASH, with gallstones reported in approximately 3% of treated patients vs. 1% placebo. Women already have higher baseline gallstone risk than men, a difference driven by estrogen's effects on bile cholesterol saturation. If you have a history of gallstones or cholecystitis, this risk needs explicit discussion before you start resmetirom.

Who This Is Right For, and Who Should Wait

Women Who Are Good Candidates

• Confirmed MASH fibrosis stage F2 or F3 (by biopsy or validated non-invasive test)
• BMI ≥25 with metabolic risk factors (the trial enrolled adults with this profile)
• Women with PCOS and documented hepatic steatosis who have progressed to significant fibrosis
• Post-menopausal women with visceral adiposity and MASH where lifestyle alone has been insufficient
• Women already on a statin for cardiovascular risk who need additional liver-specific treatment

Women Who Should Not Use Resmetirom (or Need Caution)

• Currently pregnant or planning pregnancy within the treatment period
• Breastfeeding
• Decompensated liver disease (Child-Pugh B or C): the label contraindicates use here
• Active, uncontrolled thyroid disease (discuss with your endocrinologist first)
• Child-Pugh A cirrhosis (F4 fibrosis): the trial did not enroll F4 patients, and the label does not cover this stage
• Known hypersensitivity to resmetirom or any excipient

The Evidence Gap in Women: What We Do and Do Not Know

Women have been historically under-enrolled in MASH trials, and the sex-specific data that would make prescribing resmetirom in women more precise are largely missing. A 2021 analysis of NASH clinical trials in JAMA Network Open found that only 12 of 36 trials reported sex-stratified efficacy outcomes. MAESTRO-NASH did not break out response rates by menopausal status, PCOS status, or hormonal treatment (including HRT).

What we know directly from female participants in MAESTRO-NASH: women made up roughly 53% of the cohort, and the pooled results showed efficacy. What we do not know: whether perimenopausal women respond equally, whether women on hormone therapy have altered drug metabolism, and whether the gallbladder risk is higher in women than the already-elevated trial average.

Clinicians prescribing resmetirom in women are applying aggregate trial data, not female-stratified trial data. That is an honest description of where the evidence stands in early 2025.

Monitoring While on Resmetirom

Once you start resmetirom, a reasonable monitoring schedule includes:

1. Liver enzymes (ALT, AST) and lipid panel at 4 to 8 weeks, then every 3 to 6 months
2. TSH at baseline, 8 to 12 weeks, then annually (or more frequently if on thyroid replacement)
3. Gallbladder ultrasound if symptoms suggest biliary pathology (not routinely required but clinically appropriate with new right-upper-quadrant pain)
4. Non-invasive fibrosis re-assessment at 12 months (FibroScan or MRI-PDFF) to evaluate treatment response
5. Pregnancy test if menstrual irregularity develops on treatment, particularly in PCOS patients where cycle irregularity is common

The FDA-approved prescribing information does not specify a mandatory monitoring schedule, leaving this to clinical judgment. The schedule above reflects the approach described in published hepatology expert commentary.

Cost, Access, and Telehealth Considerations

Resmetirom's list price as of launch was approximately $47,400 per year. Prior authorization from most major insurers requires documentation of F2, F3 fibrosis and either a biopsy report or a validated non-invasive staging result. Telehealth prescribing of resmetirom is possible where state law permits, but the fibrosis staging documentation requirement means you will need specialist records before a telehealth prescriber can proceed. Women using WomanRx for metabolic and liver health concerns should bring any existing hepatology records, FibroScan results, and recent metabolic labs to their first visit.