DISEASE CHARACTERISTICS:

* Patients must be women with histologically confirmed estrogen receptor (ER)- and/or progesterone receptor (PgR)-positive invasive carcinoma of the breast with no evidence of metastatic disease (M0)
* Patients must have completed mastectomy or breast-sparing surgery and must have recovered from all side effects of the surgery
* Patients must have aromatase inhibitor (AI)-associated musculoskeletal symptoms that began or increased after starting AI therapy; new musculoskeletal pain must not be due specifically to fracture or traumatic injury
* Patients must have completed the S1202 Brief Pain Inventory-Short Form (BPI-SF) within 7 days prior to registration; patients must have an "average pain" of at least 4 on the BPI-SF

PATIENT CHARACTERISTICS:

* Patients must be post-menopausal, as defined by at least one of the following:

* At least 12 months since the last menstrual period
* Prior bilateral oophorectomy
* Previous hysterectomy with one or both ovaries left in place (or previous hysterectomy in which documentation of bilateral oophorectomy is unavailable) AND follicle-stimulating hormone (FSH) values consistent with the institutional normal values for the post menopausal state; if patient is under the age of 55, FSH levels must be obtained within 28 days prior to registration OR
* Have been on LHRH agonist therapy for at least 3 months and estradiol levels drawn within 28 days prior to registration are consistent with the institutional normal values for post-menopausal state.
* Patients must have Zubrod performance status of 0-2
* Patients must have no known allergy or hypersensitivity to duloxetine or any of the inactive ingredients in the matching placebo
* Patients must not have any contraindicated concurrent illnesses listed on the duloxetine package insert including:

* Current primary psychiatric diagnosis (schizophrenia, psychosis) or suicidal ideation, history of bipolar disorder, or seizure disorder
* History of alcohol or other substance abuse or dependence within 365 days prior to registration
* Chronic liver disease
* End-stage renal disease
* Uncontrolled narrow-angle glaucoma
* Clinically significant coagulation disorder
* Creatinine clearance \> 30 mL/min
* Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) both within 3 x upper limit of normal
* Total bilirubin within the upper limit of normal
* Patients must be able to complete study questionnaires in English or Spanish
* Patients must not have concurrent medical/arthritic disease that could confound or interfere with evaluation of pain or efficacy including: inflammatory arthritis (rheumatoid arthritis, systemic lupus, spondyloarthropathy, psoriatic arthritis, polymyalgia rheumatica), or cancer involving the bone
* Patients must be willing to submit blood samples for correlative studies; baseline samples must be obtained prior to beginning protocol treatment

PRIOR CONCURRENT THERAPY:

* See Disease Characteristics
* If patients were treated with chemotherapy and/or radiation therapy, these treatments must be completed at least 28 days prior to study registration
* Concurrent bisphosphonate and trastuzumab therapies are allowed
* Patients should have recovered from all Grade 2 or higher side effects of chemotherapy and/or radiation therapy with the exception of alopecia and peripheral neuropathy
* Patients must currently be taking one of the following aromatase inhibitor (AI) doses for at least 21 days, but no longer than 12 months, prior to registration and plans to continue for at least an additional 180 days after registration

* Anastrozole (Arimidex®) 1 mg daily
* Letrozole (Femara®) 2.5 mg daily
* Exemestane (Aromasin®) 25 mg daily
* Patients must not be taking any contraindicated medications listed on the duloxetine package insert including the following: treatment with phenothiazines, propafenone, flecainide, or linezolid; treatment with monoamine oxidase (MAO)-inhibitor within 14 days prior to registration; or current use of anticoagulation medication (e.g., heparin, warfarin)
* Patients must not require selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephirine reuptake inhibitors (SNRIs), or tricyclic antidepressants during study participation; patients must have been able to taper and discontinue treatment with these medications at least 7 days prior to registration; patients must not have taken duloxetine or milnacipran within 90 days prior to registration
* Patients who are receiving treatment with narcotics, tramadol, gabapentin, and/or pregabalin must have been taking a stable dose for at least 30 days prior to registration