Licorice Root Extract and Docetaxel in Treating Patients With Metastatic Prostate Cancer That Did Not Respond to Hormone Therapy

DISEASE CHARACTERISTICS: * Diagnosis of prostate adenocarcinoma * Metastatic disease * Must have failed initial hormonal therapy and have disease progression after at least one chemotherapy regimen\*, meeting any of the following criteria: * Progressive PSA ≥ 5 ng/mL, as evidenced by 2 separate measurements taken ≥ 2 weeks apart with the second PSA measurement greater than the first one and PSA measurement at screening greater than the first one * Progressive measurable disease (e.g., changes in the size of lymph nodes or parenchymal masses or appearance of new lesions on physical examination or x-ray/CT scan) with a PSA level at screening ≥ 5 ng/mL * Progressive bone metastasis (e.g., presence of new lesions on a bone scan) with a PSA level at screening ≥ 5 ng/mL NOTE: \*Prior chemotherapy must include a taxane therapy, but disease progression does not have to follow taxane therapy * Patients must maintain primary androgen ablation (hormonal) therapy AND experience disease progression while not receiving antiandrogen therapy PATIENT CHARACTERISTICS: * ECOG performance status 0-1 * Life expectancy ≥ 6 months * Absolute neutrophil count ≥ 1,500/mm\^3 * Platelet count ≥ 100,000/mm\^3 * WBC ≥ 3,500/mm\^3 * Bilirubin ≤ 1.2 mg/dL * Creatinine ≤ 1.5 mg/dL * SGOT or SGPT ≤ 1.5 times upper limit of normal * No other prior malignancy unless treated with curative intent and free of disease for the time period considered appropriate for the specific cancer * No uncontrolled hypertension * No active infections * No known HIV positivity * No uncontrolled medical condition that would preclude study therapy * No diagnosis of major depression or suicidal ideation * No problems with oral absorption PRIOR CONCURRENT THERAPY: * See Disease Characteristics * More than 4 weeks since prior surgery or radiotherapy and recovered * At least 4 weeks since prior flutamide * At least 6 weeks since prior bicalutamide * No prior or concurrent herbal supplements or thiazide diuretics * No other concurrent investigational or commercial agents or therapies