This study is for prostate cancer patients taking hormone therapy treatments. Hormone therapy for prostate cancer is a treatment that can stop or reduce the male hormone, testosterone and is also called androgen deprivation therapy. Androgen deprivation therapy (ADT) or hormone therapy for prostate cancer includes medications to stop the body from producing testosterone or surgery to remove the testicles.
   
Because hormone therapy treatment can cause hot flashes, this study aims to test whether a low or high dose of oxybutynin can reduce these hot flashes. The goal of this study is to determine whether the study drug, oxybutynin, does actually decrease hot flashes, how much it decreases hot flashes, and what side effects it might cause. 

Oxybutynin is currently approved by the U.S. Food and Drug Administration (FDA) to treat symptoms of overactive bladder, such as loss of bladder control or a frequent need to urinate. There is evidence that this medication decreases hot flashes in women, and it is possible that it might decrease hot flash symptoms in men, but oxybutynin is not currently approved by the FDA to treat hot flashes in men.

The effects of oxybutynin will be compared to a placebo. The study placebo is a liquid that looks like the study drug, but contains no medication. Participants will be randomized into 1 of 4 study groups. There is an equal chance of being assigned to each group.

Group 1 will receive a low dose of oxybutynin and group 2 will receive a low dose of placebo. Both of these groups will receive 2.5 mL in liquid form.

Group 3 will receive a high dose of oxybutynin and group 4 will receive a high dose of placebo.  Both of these groups will receive 5.0 mL in liquid form.

All participants will complete daily hot flash diaries, symptom experience questionnaires, and a hot flash related daily interference scale at different time points throughout the study. These should take no longer than 20 minutes to complete each time. A study coordinator or nurse will also call participants once each week for the full 7-week period to answer any questions and assess any side effects.