Hormonal therapy

This therapy is likely to be used in cases in which the cancer has spread to distant regions. The goal of hormonal therapy is to lower levels of testosterone or to stop testosterone from working. Prostate cancer is stimulated by testosterone and other male hormones (androgens). These effects on testosterone can be achieved with surgery or with drug treatment. Often, the initial response is good, but cancer may progress over time.  

The testes produce much of the testosterone that stimulates cancer growth. Surgical removal of both testicles (castration, or orchiectomy) is the best way to stop hormonal stimulation of the tumor.
 
Men usually prefer medical castration to surgical castration. A luteinizing hormone-releasing hormone (LHRH) agonist, such as leuprolide (Lupron, Viadur, Eligard), goserelin (Zoladex), or buserelin (Suprefact), stops the production of testosterone.
 
Agents that stop testosterone from working, such as flutamide (Eulexin) or bicalutamide (Casodex), are called anti-androgens. They are typically used after orchiectomy or with an LHRH agonist to more completely suppress the effects of testosterone on the cancer.
 
Drugs that stop the adrenal glands from making androgens are sometimes used.
 
Estrogen, in the form of diethylstilbestrol, can also be used to suppress testosterone. Because of its extensive side effects, estrogen is not used very often.
 
Side effects of these medications vary. Orchiectomy and LHRH agonists may cause impotence, hot flashes, and loss of sexual desire. Antiandrogens may cause nausea, vomiting, diarrhea, and breast enlargement or tenderness. Any of these therapies can weaken bones.

Source http://www.emedicinehealth.com