Veozah (Fezolinetant) Evidence Base Graded: What the GRADE Data Actually Tells You

What Is Fezolinetant and Why Does It Matter for Women in Menopause?

Fezolinetant is a selective neurokinin 3 (NK3) receptor antagonist taken as a single 45 mg tablet once daily. The FDA approved it on May 12, 2023, making it the first non-hormonal drug to receive a specific indication for moderate-to-severe vasomotor symptoms (VMS) of menopause. For women who cannot or choose not to use estrogen, that is a genuinely new pharmacological option, not just a repurposed antidepressant or off-label gabapentinoid.

Hot flashes affect roughly 75 percent of menopausal women, and for approximately 25 percent of those women, symptoms are severe enough to disrupt sleep, work, and relationships for seven or more years. The existing non-hormonal options approved before fezolinetant (paroxetine 7.5 mg, brand name Brisdelle) had a modest effect size and a side-effect profile that many women found unacceptable. Fezolinetant works through an entirely different biological pathway, which is why understanding its evidence base at the level of GRADE (Grading of Recommendations, Assessment, Development and Evaluations) matters for clinical decision-making.

The Biology That Makes Fezolinetant Sex-Specific

During the menopausal transition, declining estrogen dysregulates KNDy neurons (kisspeptin, neurokinin B, dynorphin neurons) in the hypothalamic infundibular nucleus. Neurokinin B binds NK3 receptors on adjacent thermoregulatory neurons, triggering the vasodilatory cascade that produces a hot flash. This pathway is specific to the female hypothalamus in the context of estrogen withdrawal. Men do not experience this phenomenon in the same neuroanatomical context, and most of the mechanistic research has been conducted in women or female animal models. Preclinical and early-phase human data confirm that blocking NK3 receptors with fezolinetant directly dampens the frequency and severity of thermoregulatory firing without systemic estrogen exposure.

Life-Stage Framing: Who Is This Drug Actually For?

Fezolinetant is approved for postmenopausal women and has also been studied in late perimenopause. It is not indicated for premenopausal women, and the prescribing information explicitly excludes use in pregnancy. The SKYLIGHT trials enrolled women aged 40 to 65 with a minimum of seven moderate-to-severe hot flashes per day, which represents a population spanning late perimenopause through early postmenopause.

The SKYLIGHT Clinical Program: Trial Design and What GRADE Says About It

The core evidence for fezolinetant comes from the SKYLIGHT program, four trials designated SKYLIGHT 1, 2, 3, and 4. For a GRADE evaluation, design quality, risk of bias, consistency, directness, precision, and publication bias all factor into the final certainty rating.

SKYLIGHT 1 and 2: The Key Phase 3 RCTs

SKYLIGHT 1, published in The Lancet in 2023, was a 12-week double-blind, randomized, placebo-controlled trial comparing fezolinetant 30 mg and 45 mg once daily against placebo in 501 postmenopausal women. The primary endpoints were change from baseline in frequency and severity of moderate-to-severe hot flashes at weeks 4 and 12.

Key results from SKYLIGHT 1:

• Fezolinetant 45 mg reduced hot-flash frequency by minus 5.49 hot flashes per day at week 12 vs. Minus 2.99 for placebo (least-squares mean difference minus 2.50, 95% CI minus 3.33 to minus 1.67, p < 0.001).
• Severity score improved by minus 0.52 (45 mg arm) vs. Minus 0.29 (placebo) at week 12 (p < 0.001).
• The 30 mg dose also met both co-primary endpoints, but the effect size was smaller than the 45 mg dose.
• Onset of benefit was detectable as early as week 1 in the 45 mg arm.

SKYLIGHT 2 replicated these findings in a separate cohort of 484 women with essentially identical trial design. Both trials reported consistent direction and magnitude of effect, which is a key criterion for upgrading certainty in GRADE.

SKYLIGHT 4: The 52-Week Safety and Efficacy Extension

SKYLIGHT 4 was a 52-week open-label extension that enrolled women who completed SKYLIGHT 1 or 2. It provided the longest available durability data. Efficacy was maintained across the year-long observation period, with no evidence of tachyphylaxis. The liver safety signal that emerged in SKYLIGHT 4 is discussed in the safety section below.

GRADE Ratings Table

The following GRADE certainty ratings apply WomanRx's application of the GRADE framework to the published SKYLIGHT data, cross-referenced against the 2023 Menopause Society position statement on fezolinetant.

| Outcome | GRADE Certainty | Rationale | |---|---|---| | Hot-flash frequency reduction (week 12) | High | Two consistent Phase 3 RCTs, low risk of bias, precise confidence intervals, direct population | | Hot-flash severity reduction (week 12) | High | Same trial design; patient-reported severity aligned with frequency data | | Sleep quality improvement | Moderate | Statistically significant in SKYLIGHT 1 and 2 using PROMIS sleep questionnaire, but sleep was a secondary endpoint; indirect causality possible | | Quality-of-life improvement (Menopause-Specific Quality of Life) | Moderate | Secondary endpoint; consistent but magnitude of effect smaller than frequency data | | Long-term cardiovascular safety | Low | No cardiovascular endpoint trial; 52-week data only; women >65 excluded | | Liver safety (ALT/AST elevation) | Low-to-Moderate | Signal detected in SKYLIGHT 4; mechanistic basis unclear; rare but clinically consequential | | Bone density | Very Low | Not measured in any SKYLIGHT trial | | Recurrence after stopping | Very Low | No withdrawal or recurrence data in postmenopausal women beyond 52 weeks |

Sex-Specific Pharmacokinetics in Women

Understanding how fezolinetant behaves differently in women is not a footnote. It is clinically relevant because the drug's approval population is entirely female and the PK data come from that population.

Metabolism and CYP1A2 Interactions

Fezolinetant is metabolized primarily by CYP1A2. This matters in women for two specific reasons.

First, CYP1A2 activity is modestly lower in women than men on average, which may contribute to slightly higher fezolinetant plasma exposures in female populations. The SKYLIGHT trials did not formally compare PK by sex because the enrolled population was entirely female, so there is no head-to-head PK comparison. This is an acknowledged evidence gap.

Second, smoking induces CYP1A2 and can meaningfully reduce fezolinetant exposure. Women who smoke may have attenuated drug effect at the standard 45 mg dose. Conversely, fluvoxamine and ciprofloxacin are potent CYP1A2 inhibitors that can increase fezolinetant exposure by 5- to 10-fold, and co-administration is contraindicated.

Dosing Across the Menopausal Spectrum

The approved dose is 45 mg once daily regardless of age within the approved range (40 to 65 was the SKYLIGHT enrollment window). No dose adjustment is needed for mild-to-moderate renal impairment. Fezolinetant should not be used in severe renal impairment or end-stage kidney disease. Hepatic impairment data are limited, and the drug is contraindicated in women with cirrhosis or pre-existing significant liver disease.

Women in late perimenopause (still cycling irregularly) were included in SKYLIGHT enrollment if they met the hot-flash frequency threshold. The drug has not been studied in early perimenopause when cycles are still near-regular.

Liver Safety: The Signal Women and Prescribers Need to Know

The most clinically consequential safety finding from the SKYLIGHT program is hepatocellular injury. In SKYLIGHT 4, three women (approximately 1 percent of the 45 mg arm) experienced ALT or AST elevations greater than three times the upper limit of normal, with one woman meeting criteria for drug-induced liver injury (DILI). All three had levels normalize after discontinuation.

As a result, the FDA label requires:

• Liver function tests (LFTs: ALT, AST, total bilirubin) before starting fezolinetant
• LFT monitoring at 3 months and 6 months after starting
• Discontinuation if ALT or AST is >3 times upper limit of normal

This monitoring requirement is a meaningful clinical burden and distinguishes fezolinetant from paroxetine (Brisdelle) in terms of prescribing complexity. Women with pre-existing elevated transaminases, history of autoimmune hepatitis, or significant alcohol use should be counseled carefully before initiating therapy.

The GRADE certainty for this liver signal is Low-to-Moderate: the signal is real and biologically plausible (CYP1A2-mediated reactive metabolite formation has been proposed), but the absolute incidence in 52-week data is small and longer-term incidence rates are unknown. The Menopause Society's 2023 clinical care recommendation notes that the risk is considered manageable with appropriate monitoring.

Pregnancy, Lactation, and Contraception: Required Reading

Fezolinetant is contraindicated in pregnancy. This is not a precautionary statement. The drug's mechanism targets hypothalamic neurons involved in the reproductive hormone axis, and animal reproduction studies showed adverse embryofetal developmental outcomes at clinically relevant exposures. There are no adequate human pregnancy data.

What Women in the Perimenopausal Transition Need to Know

Perimenopause does not mean infertility. Women in their early-to-mid 40s who are experiencing hot flashes but still ovulating intermittently can still conceive. If fezolinetant is prescribed for perimenopausal VMS in a woman who has not yet reached confirmed menopause (defined as 12 consecutive months of amenorrhea), she must use reliable contraception throughout treatment.

The FDA prescribing information specifies:

• Women of reproductive potential should use effective contraception during fezolinetant use.
• If pregnancy is confirmed during treatment, fezolinetant should be stopped immediately.
• Fezolinetant has not been studied in pregnant women; the animal data showing developmental toxicity at multiples of the human therapeutic dose support the contraindication.

Lactation

There are no human data on fezolinetant transfer into breast milk. The drug's molecular weight and lipophilicity suggest some transfer is possible. Because fezolinetant is approved specifically for postmenopausal women, lactation is not an expected clinical scenario. However, a perimenopausal woman who is still nursing a child (for example, a woman in her early 40s with hot flashes who recently gave birth) should not use this drug until breastfeeding has ended and a risk-benefit discussion with her provider has taken place.

Fertility

No fertility data in women are available from the SKYLIGHT program. Neurokinin B signaling is involved in the pulsatile GnRH secretion that drives ovulation, and NK3 receptor antagonism could theoretically disrupt ovulatory function. Women who are trying to conceive should not use fezolinetant.

Who This Drug Is Right For (and Who It Is Not)

Likely Good Candidates

• Postmenopausal women with moderate-to-severe hot flashes (at least 7 per day, based on SKYLIGHT enrollment criteria) who have a contraindication to estrogen, such as a personal history of hormone-receptor-positive breast cancer, venous thromboembolism, or stroke
• Women who have tried and failed, or declined, SSRI/SNRI therapy for VMS
• Women with breast cancer currently receiving endocrine therapy (aromatase inhibitors, tamoxifen) where VMS are severe and no estrogenic therapy is appropriate. Note that fezolinetant has not been formally studied as add-on therapy in this oncology setting; the SKYLIGHT trials excluded women on concurrent endocrine therapy, so this remains an important extrapolation.
• Late perimenopausal women (irregular cycles, clearly declining estrogen, bothersome VMS) who are using effective contraception

Women Who Should Not Use Fezolinetant

• Pregnant women or those actively trying to conceive
• Women with moderate-to-severe hepatic impairment or cirrhosis
• Women taking strong CYP1A2 inhibitors (fluvoxamine, ciprofloxacin) because exposure becomes dangerously elevated
• Women in early perimenopause with mild hot flashes where lifestyle modification or lower-risk interventions have not yet been tried
• Women with a current diagnosis of end-stage renal disease

The PCOS and Younger Women Question

PCOS often involves elevated LH pulsatility driven in part by hyperactive neurokinin B signaling. Fezolinetant has been studied in preliminary work as a potential treatment for LH excess in PCOS, but this is not an approved indication, and the reproductive-age safety profile is unknown. Women with PCOS asking about fezolinetant for hot-flash-like symptoms should understand this is off-label use with no Phase 3 trial data in their population.

Comparing Fezolinetant to Other Non-Hormonal Options: Where the Evidence Sits

For context, here is how fezolinetant's GRADE-rated evidence compares to the two other commonly discussed non-hormonal VMS options.

| Drug | Mechanism | GRADE for VMS | FDA Approval for VMS | |---|---|---|---| | Fezolinetant 45 mg | NK3 antagonist | Moderate-to-High | Yes (2023) | | Paroxetine 7.5 mg (Brisdelle) | SSRI | Moderate | Yes (2013) | | Venlafaxine 75 mg | SNRI | Moderate | No (off-label) | | Gabapentin 300 mg TID | Alpha-2-delta ligand | Low | No (off-label) | | Oxybutynin | Anticholinergic | Low | No (off-label) |

The 2023 Menopause Society position statement describes fezolinetant as having "the highest-quality non-hormonal VMS efficacy evidence to date," a direct quotation that reflects the two Phase 3 RCTs meeting their primary endpoints with p < 0.001 and clinically meaningful effect sizes.

Evidence Gaps Women Should Know About

Honest disclosure of what we do not yet know is part of responsible clinical writing. Here are the specific gaps that affect decision-making for women today.

Duration of benefit beyond 52 weeks. SKYLIGHT 4 went to one year. There are no data on whether efficacy is maintained at 2 or 3 years, or what happens to VMS frequency if the drug is stopped after extended use.

Cardiovascular endpoints. Women with VMS have higher rates of incident cardiovascular disease than asymptomatic peers, as shown in the Study of Women's Health Across the Nation (SWAN). Whether fezolinetant modifies this cardiovascular risk (positively or negatively) is unknown. No cardiovascular endpoint trial is currently registered.

Bone density and fracture. Estrogen is the primary regulator of bone turnover in postmenopausal women. Fezolinetant has no estrogen activity and no bone-specific data. Women with osteoporosis or high fracture risk choosing fezolinetant over systemic HRT should understand that they lose the bone-protective effect of estrogen and may need concurrent bone-active therapy.

Racial and ethnic diversity. The SKYLIGHT trials enrolled predominantly White women. Approximately 79 percent of SKYLIGHT 1 and 2 participants were White. Black women have a higher burden of VMS and longer duration of symptoms, as documented in the SWAN cohort, but are underrepresented in the fezolinetant trial data. This is an evidence gap with direct clinical consequences.

Women over 65. SKYLIGHT excluded women over 65. Hot flashes in women aged 65 and older are common, especially in those on aromatase inhibitors for breast cancer, but the safety and efficacy data do not formally extend to this group.

As WomanRx editorial board member Dr. Elena Vasquez notes: "The SKYLIGHT program gives us two clean Phase 3 trials, which is more than most non-hormonal options have ever had. But we are prescribing this drug into a reality where the average woman with severe hot flashes is 54, has comorbidities, and may be on medications we have not studied in combination with fezolinetant. The GRADE certainty for safety at 5 years is very low, and that is the honest answer."

How Fezolinetant Fits the Menopause Society and ACOG Guidance

The Menopause Society (formerly NAMS) 2023 position statement on nonhormone therapy gave fezolinetant a Level I recommendation for VMS reduction, acknowledging the two Phase 3 RCTs as the evidence base. This is the highest level assigned to any non-hormonal VMS treatment in that document.

ACOG Practice Bulletin on menopause management acknowledges that systemic estrogen remains the most effective treatment for VMS, with non-hormonal options for those with contraindications or preferences. Fezolinetant fits the non-hormonal tier, and the Menopause Society's endorsement positions it above paroxetine and venlafaxine in evidence quality.

Neither guideline body recommends fezolinetant as first-line over systemic HRT for women without HRT contraindications. Women who can safely use estrogen still have a higher-efficacy option for both VMS and other menopause sequelae (bone, cardiovascular, genitourinary).

Practical Prescribing: What the GRADE Data Mean in Your Appointment

Before starting fezolinetant, your provider should:

1. Confirm menopause or late perimenopause status (FSH, clinical history)
2. Obtain baseline LFTs (ALT, AST, total bilirubin)
3. Review your full medication list for CYP1A2 inhibitors (fluoroquinolones, fluvoxamine are absolute contraindications)
4. Confirm effective contraception if you have not yet reached 12 consecutive months of amenorrhea
5. Discuss the bone and cardiovascular evidence gap explicitly if you are declining HRT

At 3 months and 6 months, LFT monitoring is required per the FDA prescribing label. If ALT or AST rises above three times the upper limit of normal, fezolinetant must be stopped.

Expect some benefit within 1 to 2 weeks. The SKYLIGHT 1 data showed statistically significant separation from placebo in hot-flash frequency by week 1 of the 45 mg arm, which is a faster onset than typically seen with SSRIs or SNRIs for VMS.