Hot flashes are the most common reason women going through menopause seek medical attention. Hormone replacement therapy, or HRT, is most often prescribed to treat hot flashes. However, HRT can't be used by all women or for as long as may be needed.

Researchers want to find other ways to treat hot flashes. Fezolinetant is a medicine to treat hot flashes in women going through menopause. Fezolinetant is an approved medicine in the US. Further studies are needed before it is available in other regions such as Asia.

This study will confirm if fezolintant helps reduce the number of hot flashes in Japanese women going through menopause.

Women that want to take part in the study will be given an electronic handheld device with an app to track their hot flashes. Some women may be able to use the app on their own smartphone. Before the women are assigned a treatment, they will record information about their hot flashes.

Women will either take a lower or higher dose of fezolinetant, or a placebo. This is decided by chance alone. The placebo looks like fezolinetant but will not have any medicine in it.

The women will take 2 tablets of the study medicine (lower or higher dose of fezolinetant, or the placebo) once a day for up to 12 weeks. They will either take 1 tablet of fezolinetant (higher or lower dose) and 1 placebo tablet, or they will take 2 placebo tablets. The women will continue to record information about their hot flashes on the electronic device or their smartphone.

During the study, the women will visit the study clinic a few times. At each visit they will be asked if they had any medical problems and will use an electronic device at the clinic to answer questions about how the hot flashes affect their daily life. Other checks will include a medical examination, vital signs (temperature, blood pressure and pulse). Some blood and urine samples will be taken for laboratory tests. At some visits, the women will also have an ECG to check their heart rhythm. Women who have a womb (uterus) will also have a test called a transvaginal ultrasound. A probe is gently placed inside the vagina. Sound waves will create a picture of the organs in the pelvis. This will allow the study doctor to look more closely at the uterus and surrounding organs.

The last clinic visit will be 3 weeks after the women take their final tablets of the study medicine (1 tablet of lower or higher dose of fezolinetant and 1 placebo tablet, or 2 placebo tablets).

Inclusion Criteria:

• Participant confirmed as menopausal per one of the following criteria at the screening visit (visit 1):

  • Spontaneous amenorrhea for >/=12 consecutive months;
  • Spontaneous amenorrhea for >/=6 months with biochemical criteria of menopause (follicle-stimulating hormone (FSH) > 40 IU/L);
  • Having had bilateral oophorectomy >/=6 weeks prior to the screening visit (visit 1) (with or without hysterectomy); or
  • Having had hysterectomy without bilateral oophorectomy with the biochemical criteria of menopause (FSH > 40 IU/L).

• Participant must be seeking treatment or relief for vasomotor symptoms (VMS) associated with menopause and meet some set criteria related to hot flash(es) (HFs) (VMS) prior to randomization.

• Participant agrees not to participate in another interventional study while participating in the present study.

Exclusion Criteria:

• Participant has a history of an undiagnosed uterine bleeding within the 6 months prior to the screening visit (visit 1).
• Participant has a current malignant tumor or history (except for a participant who has not received treatment for malignant tumors for at least 5 years before informed consent acquisition and was not considered to have recurrence) of a malignant tumor except for non-metastatic basal cell carcinoma of the skin.
• Participant has a medical condition or chronic disease (including history of neurological [including cognitive], hepatic, renal, cardiovascular, gastrointestinal, pulmonary [e.g., moderate asthma], endocrine, or gynecological disease) that could confound interpretation of the study outcome.
• Participant uses a prohibited therapy (hormone therapy, hormone replacement therapy (HRT), hormonal contraceptive, any treatment for menopausal symptoms [prescription medications, over-the-counter, or herbal/Kampo medicines] or strong or moderate cytochrome P450 1A2 (CYP1A2) inhibitors) and is not willing to wash out or discontinue use of such drugs from screening visit (visit 1) through the follow-up visit (visit 6) or it is not medically appropriate to discontinue such drugs for the duration of the study.
• Participant has been randomized/registered in a clinical study with fezolinetant previously or had previous exposure to marketed fezolinetant elsewhere.
• Participant has a present or previous history of participation in this study.
• Participant has received any investigational therapy within 28 days or 5 half-lives, whichever is longer, prior to screening (visit 1).
• Participant has an unacceptable result from the transvaginal ultrasound (TVU) assessment at screening (i.e., full length of endometrial cavity cannot be visualized or presence of clinically significant abnormal findings).
• Participant has documentation of a clinically significant abnormal Papanicolaou (Pap) test (or equivalent cervical cytology) within the 12 months prior to the screening visit (visit 1) or at screening.
• Participant has active liver disease, jaundice, or elevated liver aminotransferases (alanine aminotransferase (ALT) or aspartate aminotransferase (AST)), elevated total bilirubin (TBL) or direct bilirubin (DBL), elevated international normalized ratio (INR), or elevated alkaline phosphatase (ALP) at screening. A participant with mildly elevated ALT or AST up to < 1.5 × upper limit of normal (ULN) can be enrolled if TBL and DBL are normal. Participant with mildly elevated ALP (up to < 1.5 × ULN) can be enrolled if cholestatic liver disease is excluded and no cause other than fatty liver is diagnosed. Participant with Gilbert's syndrome with elevated TBL may be enrolled as long as DBL, hemoglobin and reticulocytes are normal.
• Participant has creatinine > 1.5 × ULN or estimated glomerular filtration rate using the Modification of Diet in Renal Disease formula \

Access to anonymized individual participant level data collected during the study, in addition to study-related supporting documentation, is planned for studies conducted with approved product indications and formulations, as well as products terminated during development. Studies conducted with product indications or formulations that remain active in development are assessed after study completion to determine if Individual Participant Data can be shared. Further details on Astellas' data sharing policy can be found at https://www.clinicaltrials.astellas.com/transparency/.

Access to participant level data is offered to researchers after publication of the primary manuscript (if applicable) and is available as long as Astellas has legal authority to provide the data.

Researchers must submit a proposal to conduct a scientifically relevant analysis of the study data. The research proposal is reviewed by an Independent Research Panel. If the proposal is approved, access to the study data is provided in a secure data sharing environment after receipt of a signed Data Sharing Agreement.