Dextromethorphan in Treating Patients With Fatigue Caused by Cancer

DISEASE CHARACTERISTICS: * Diagnosis of malignancy * Must be undergoing active treatment for malignancy which may include hormonal therapy (e.g., tamoxifen citrate or leuprolide acetate), but not radiotherapy alone * Fatigue score ≥ 4 on a verbal analogue scale of 0 to 10 * No untreated cancer-related anemia PATIENT CHARACTERISTICS: * Hemoglobin \> 10 g/dL * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * Able to swallow pills * No known allergy to dextromethorphan hydrobromide * No patients known to be phenotypically poor metabolizers of CYP2D6 * No untreated hypothyroidism PRIOR CONCURRENT THERAPY: * See Disease Characteristics * Prior single-dose inhibitors (e.g., ranitidine or cimetidine) for hypersensitivity prophylaxis allowed * Erythropoietic growth factor therapy of \> 8 weeks duration allowed * No concurrent CYP2D6 inducers or inhibitors * No concurrent monoamine oxidase inhibitors * No other concurrent medications containing dextromethorphan hydrobromide * No concurrent over-the-counter medication, herbal product, vitamin, food supplement, or any other type of special product unless permission to continue use is obtained from the Principal Investigator * No other concurrent anticancer investigational agents or therapies