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.

In this study fezolinetant will be used to treat hot flashes in Japanese women going through menopause. This study will confirm the safety of fezolinetant and how well the women tolerate the treatment.

Women will either take 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 1 tablet of the study medicine (fezolinetant or the placebo) once a day for up to 52 weeks.

During the study, the women will visit their study clinic for a check-up about every 4 weeks for up to 52 weeks (1 year). At each visit they will be asked if they had any medical problems. Other checks will include a medical examination and vital signs (temperature, blood pressure and pulse). At some visits, the women will have an ECG to check their heart rhythm and some blood and urine samples will be taken for laboratory tests. During a couple of visits, 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 tablet of the study medicine (fezolinetant or the placebo).

Inclusion Criteria:

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

  • For a post-menopausal participant: 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); Having had hysterectomy without bilateral oophorectomy with the biochemical criteria of menopause (FSH > 40 IU/L); or Having been confirmed to be post-menopausal in the 2693-CL-0310 study.
  • For a peri-menopausal participant: Spontaneous amenorrhea for >/=60 days but < 6 consecutive months 2 times in the 2 most recent menstrual cycles with biochemical criteria of peri-menopause (FSH > 25 IU/L); or Spontaneous amenorrhea for >/=6 months but < 12 consecutive months with biochemical criteria of peri-menopause (FSH > 25 IU/L and ≤ 40 IU/L); Having had hysterectomy without bilateral oophorectomy with the biochemical criteria of peri-menopause (FSH > 25 IU/L and ≤ 40 IU/L).

• Participant is seeking treatment for relief of vasomotor symptoms (VMS) associated with menopause.

• Female participant:

  • Is not pregnant and at least 1 of the following conditions apply: Not a women of childbearing potential (WOCBP); WOCBP who has a negative urine pregnancy test day 1 (visit 2) and agrees to follow the contraceptive guidance from the time of informed consent through at least 21 days after final study intervention administration.
  • Must not be breastfeeding or lactating starting at screening and throughout the investigational period and for 21 days after final study intervention administration.
  • Must not donate ova starting at first administration of study intervention and throughout the investigational period and for 21 days after final study intervention administration

• 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 VMS [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 16) or it is not medically appropriate to discontinue such drugs for the duration of the study.
• Participant has been randomized/registered in a clinical trial 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 (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 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.