Fezolinetant: Non-Hormonal Drug Targets Brain Pathway

How Does Fezolinetant Treat Hot Flashes Without Hormones?

Hot flashes are driven by a neural circuit in the hypothalamus involving so-called KNDy neurons, named for the neuropeptides they express: kisspeptin, neurokinin B, and dynorphin. As estrogen declines during menopause, these neurons become hypertrophied and hyperactive, releasing more neurokinin B onto the thermoregulatory center and triggering the sudden heat sensation, sweating, and flushing characteristic of vasomotor symptoms.

Fezolinetant, marketed as Veozah by Astellas Pharma, is a selective antagonist at the neurokinin 3 (NK3) receptor. By blocking neurokinin B from binding this receptor, the drug dampens KNDy neuron overactivity and stabilizes the brain's temperature set point. Crucially, this mechanism does not rely on replacing estrogen, so it avoids the breast and uterine tissue stimulation that limits hormone therapy use in some patients.

What Did the Pivotal Clinical Trials Show?

The FDA approval of fezolinetant in May 2023 was based primarily on the SKYLIGHT 1 and SKYLIGHT 2 randomized, double-blind, placebo-controlled phase 3 studies, with longer-term safety supported by SKYLIGHT 4. Across these trials, women receiving fezolinetant reported meaningful reductions in both how often and how severely they experienced vasomotor symptoms, with separation from placebo evident within the first weeks of treatment.

The most clinically important safety signal has involved the liver. Following post-marketing reports of hepatotoxicity, the FDA added a boxed warning about rare but serious liver injury, and prescribers are advised to monitor liver function before and during therapy. Common adverse effects in trials included abdominal pain, diarrhea, insomnia, back pain, and elevated hepatic enzymes, while the drug did not show the cardiovascular or breast safety concerns historically associated with systemic estrogen.

Who Should Consider This Drug Instead of Hormone Therapy?

Hormone therapy remains the most effective treatment for vasomotor symptoms and is recommended by the Menopause Society as first-line for many symptomatic women under age 60 or within 10 years of menopause onset. However, women with a history of breast cancer, certain cardiovascular conditions, prior venous thromboembolism, or active liver disease often cannot safely take systemic estrogen, leaving a significant treatment gap that non-hormonal options aim to fill.

Before fezolinetant, the main non-hormonal pharmacologic choices were low-dose paroxetine, off-label SSRIs and SNRIs, gabapentin, and clonidine, each with modest efficacy and tolerability trade-offs. A targeted central nervous system therapy that addresses the underlying KNDy circuit represents a different therapeutic strategy. Decisions about whether to choose hormone therapy, fezolinetant, or another non-hormonal agent should be individualized based on symptom severity, medical history, hepatic safety considerations, and patient preference, ideally in shared decision-making with a clinician familiar with menopause care.