Inclusion Criteria:

• 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.
• Men receiving next generation androgen axis inhibitor therapies including abiraterone, enzalutamide, apalutamide, and darolutamide are eligible.
• Patients must be on a stable dose of all hormone-directed 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.
• Patients receiving radiation therapy during the study period are eligible.
• Eligible patient must have bothersome hot flashes for ≥ 14 days prior to registration, defined by an occurrence of ≥ 28 times per week and of sufficient severity to cause the patient to seek therapeutic intervention.
• Life expectancy of greater than 6 months.
• Eastern Cooperative Oncology Group (ECOG) performance status - 0, 1, or 2.
• In order to complete the mandatory patient-completed measures, participants must be able to speak and/or read English.

Exclusion Criteria:

• No current use or future planned use of any of the following agents during the study period: drugs that are not Food and Drug Administration (FDA) approved for use in humans, androgens, estrogens, progesterone analogs, gabapentin, selective serotonin reuptake inhibitor (SSRI)/serotonin and norepinephrine reuptake inhibitor (SNRI) anti-depressants, cholinergic agonists, cholinesterase inhibitors, 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.
• No current or prior use of oxybutynin.
• Patients with a history of any of the following contraindications to oxybutynin are not eligible:
  • gastroparesis or gastrointestinal obstructive disorders;
  • significant gastric reflux symptoms not controlled by medication; ulcerative colitis;
  • narrow-angle glaucoma;
  • urinary retention requiring indwelling or intermittent self-catheterization within the prior 6 months;
  • hypersensitivity to oxybutynin or any other components of the product; current uncontrolled hyperthyroidism;
  • uncontrolled coronary artery disease or a history of myocardial infarction within the prior 12 months;
  • New York Heart Association (NYHA) class II-IV congestive heart failure;
  • symptomatic cardiac arrhythmias;
  • current uncontrolled hypertension;
  • myasthenia gravis; or
  • dementia.

Eligibility last updated 11/22/21. Questions regarding updates should be directed to the study team contact.