Hot Flash Drug Elinzanetant Shows Strong Safety Record in Pooled Analysis of Four Clinical Trials

A major pooled analysis of more than 1,500 postmenopausal women has found that elinzanetant, the first dual neurokinin-1 and neurokinin-3 receptor antagonist approved for treating hot flashes, carries a favorable long-term safety profile with no signals of liver toxicity or increased cancer risk over 52 weeks of treatment. The findings, published in eClinicalMedicine, come at a critical moment for a new drug class that has been shadowed by safety concerns surrounding its closest competitor.

Vasomotor symptoms, the hot flashes and night sweats that disrupt the lives of millions of women during menopause, are among the most frequent and debilitating symptoms of the transition. They can impair work performance, reduce quality of life, disturb sleep, and drive up healthcare costs. For decades, the mainstay of treatment was menopause hormone therapy, which works well for many women under 60 and within ten years of their final period, but is contraindicated in women with a history of hormone-sensitive cancers, prior blood clots, stroke, or liver disease. Until recently, the only FDA-approved non-hormonal option was the antidepressant paroxetine, while most other non-hormonal drugs were used off-label with modest efficacy and tolerability problems that lead up to half of users to stop within three months.

Neurokinin-targeted therapies changed that landscape. These drugs work by modulating neurokinin receptor activity in the hypothalamus, the brain region that regulates body temperature and becomes dysregulated as estrogen declines. Elinzanetant blocks both NK-1 and NK-3 receptors, and has demonstrated rapid and sustained reductions in the frequency and severity of moderate-to-severe hot flashes in the pivotal Phase III OASIS trials, along with meaningful improvements in sleep disturbance and menopause-related quality of life. But the class has faced scrutiny. Fezolinetant, a selective NK-3 antagonist, has been linked to rare but serious liver injury, prompting an FDA boxed warning for hepatotoxicity and mandatory liver function monitoring in multiple countries. An earlier NK-3 antagonist, pavinetant, had its clinical development halted in 2017 after transient transaminase rises in a Phase II trial.

To build a more comprehensive picture of elinzanetant’s safety, researchers pooled data from four randomized, placebo-controlled trials: the Phase IIb SWITCH-1 study conducted from 2018 to 2019 and the Phase III OASIS-1, -2, and -3 trials conducted from 2021 to 2024. All four enrolled postmenopausal women aged 40 to 65 experiencing moderate-to-severe vasomotor symptoms from natural or surgical menopause. The OASIS-4 trial, which studied women with hormone receptor-positive breast cancer receiving endocrine therapy, was excluded because of its substantially different population. The analysis examined two windows: a placebo-controlled period covering the first 12 weeks, in which 765 women took elinzanetant 120 mg and 754 took placebo, and a full 52-week period including 1,113 women exposed to elinzanetant.

The results showed that half of the elinzanetant group, 50.8 percent, reported at least one treatment-emergent adverse event during the first 12 weeks, compared with 43.2 percent on placebo. Most events were mild or moderate. Headache, fatigue, and somnolence were the most common events, occurring in 7.5, 5.4, and 3.4 percent of elinzanetant users respectively, versus 4.2, 1.3, and 0.5 percent on placebo. Notably, these symptoms clustered in the early weeks: their frequency was the same or lower at 52 weeks than at 12 weeks, suggesting most affected women experienced them only at the start of treatment. Serious adverse events were rare in both groups, at 1.2 percent with elinzanetant and 0.9 percent with placebo over 12 weeks, and nearly all were judged unrelated to the drug. A single serious event, a generalized tonic-clonic seizure in a participant with a long history of epilepsy, was assessed as possibly related; rare seizure cases have since appeared in post-marketing surveillance, and caution is advised for women with seizure disorders.

Discontinuation rates told a similar story of early but limited intolerance. Over 12 weeks, 7.8 percent of elinzanetant users stopped treatment because of adverse events, versus 3.6 percent on placebo, with fatigue and headache the leading causes. Crucially, the discontinuation rate did not rise between 12 and 52 weeks, indicating that women who tolerated the drug initially were unlikely to abandon it later. The authors also noted that because the trials were double-blind, background symptoms of menopause itself, or side effects of permitted concomitant medications, could have been coincidentally attributed to placebo, complicating direct comparisons.

Liver safety was the analysis’s most anticipated finding. Elevated alanine or aspartate transaminases above three times the upper limit of normal appeared in just 0.5 percent of elinzanetant users over 12 weeks and 1.2 percent over 52 weeks, rates that were statistically indistinguishable from placebo. There were no elevations of five or eight times the upper limit during the placebo-controlled period, and no cases meeting the strict Hy’s law criteria that flag potential serious drug-induced liver injury. An independent blinded liver safety monitoring board reviewed all cases meeting close-observation thresholds and judged only one elinzanetant case possibly related, in a woman with a plausible alternative cause involving possible gallstone passage; that case resolved without stopping treatment. The authors point out that elinzanetant lacks the structural features associated with hepatotoxicity and shares no similar substructures with NK-3 antagonists, and that approved NK-1 antagonists have not been linked to liver injury. Most countries do not require liver monitoring with elinzanetant, though the FDA mandates baseline testing and a repeat check at three months.

Cancer risk, a second area of concern raised during fezolinetant’s development, also showed no troubling signal. Malignant tumors were reported in five elinzanetant-treated women, including one case of invasive triple-negative breast cancer judged unrelated to treatment, and two placebo-treated women with basal cell skin cancers. The exposure-adjusted incidence rate for malignant tumors in the elinzanetant group, 0.88 per 100 person-years, was broadly consistent with the population-level rate of 0.81 observed in US women aged 50 to 64 in the SEER cancer registry, and the breast cancer rate of 0.38 aligned with a background rate of 0.29. No cases of endometrial hyperplasia or malignancy emerged in either group, an important finding given that unopposed estrogen in hormone therapy can raise endometrial cancer risk. The researchers also observed that NK-1 receptor antagonists have demonstrated anti-tumor activity in preclinical cancer models, and that elinzanetant modulates neurokinin signaling without any estrogenic effect, offering no mechanistic route to hormone-related cancers. Metabolic markers including blood pressure, cholesterol, triglycerides, and glucose remained stable throughout.

The authors are careful to frame the analysis as exploratory rather than confirmatory. It was not powered for formal hypothesis testing, three of the four trials were placebo-controlled for only 12 weeks, and the enrolled population, which excluded women with recent malignancy and abnormal liver parameters, limits generalizability. The incidence-rate calculations also assume a constant hazard over time, which can mask transient risks, and the comparison with population registry data must be interpreted cautiously given the strict eligibility criteria of clinical trials. Longer-term safety monitoring, time-to-event analyses, and real-world post-marketing evidence will be needed to fully characterize the drug’s profile, and a three-year extension study is underway in the breast cancer population from OASIS-4.

Nevertheless, the pooled data provide the most robust safety picture yet for a treatment that many clinicians view as a watershed for menopause care. For women who cannot or choose not to take hormones, and for the growing number of breast cancer survivors whose endocrine therapy triggers severe hot flashes, the findings support elinzanetant as an effective option with a tolerability profile dominated by mild, early, and self-limited central nervous system symptoms. As post-marketing surveillance accumulates in broader and more diverse populations, the drug class that once seemed jeopardized by liver warnings may be finding surer footing.

Subject of Research: Safety and tolerability of elinzanetant, a dual NK-1/NK-3 receptor antagonist for menopausal vasomotor symptoms, in a pooled analysis of four randomized clinical trials

Article Title: Safety and tolerability of elinzanetant: a pooled analysis from four randomized clinical trials

Article References: Safety and tolerability of elinzanetant: a pooled analysis from four randomized clinical trials. (n.d.). Original publication

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Keywords: elinzanetant, menopause, vasomotor symptoms, hot flashes, neurokinin receptor antagonists, liver safety, hepatotoxicity, clinical trials, breast cancer, endometrial safety, pharmacology, women's health