Age ≥ 18 years Men who are currently receiving Androgen Deprivation Therapy (ADT) for the treatment of prostate cancer. ADT is defined by a history of orchiectomy, or ongoing usage of gonadotropin-releasing hormone agonists or antagonists (e.g. leuprolide, degarelix, relugolix). Men receiving Androgen Receptor Pathway Inhibitors (ARPI) such as abiraterone, enzalutamide, apalutamide, and darolutamide are eligible. Patients must be on a stable dose of all hormonal therapies for at least 28 days prior to registration and must not be planning to discontinue this therapy for at least 42 days following registration. Additional ARPI agents (e.g. abiraterone or enzalutamide) are allowed to be added during the Extension Phase of the trial, but not during the Treatment Phase. Patients receiving radiation therapy during the study period are eligible. An eligible patient must have bothersome hot flashes for ≥ 7 days prior to consent, resulting in an average of four or more hot flashes per day of sufficient severity to cause the patient to seek therapeutic intervention. Life Expectancy of 6 months or greater. Language: In order to complete the mandatory participant-completed measures, participants must be able to speak and read English.

Current or future planned use of any of the following agents during the study period: drugs that are not FDA approved for use in humans, any drug with category X interactions with fezolinetant; androgens, estrogens, progesterone analogs, or complementary/alternative medicine taken for the purpose of managing hot flashes. Prior use of these agents is permitted as long as they are discontinued before registration. Stable dosing (≥ 1 month) of gabapentin, cholinergic agonists, cholinesterase inhibitors for other indications is permitted. History of cirrhosis Elevated alanine aminotransferase (ALT) or aspartate aminotransferase (AST) ≥ 2 X ULN or total bilirubin > ULN eGFR <30 mL/min/1.73 m2 based on reported MDRD estimate. Current use of CYP1A2 inhibitors (fezolinetant is a substrate of CYP1A2).