Duloxetine is a selective serotonin and norepinephrine reuptake inhibitor antidepressant (SSNRI). Duloxetine affects chemicals in the brain that may become unbalanced and cause depression. Duloxetine is used to treat major depressive disorder and general anxiety disorder. Duloxetine is also used to treat fibromyalgia (a chronic pain disorder), or chronic muscle or joint pain (such as low back pain and osteoarthritis pain). Duloxetine is also used to treat pain caused by nerve damage in people with diabetes (diabetic neuropathy). Duloxetine may also be used for purposes not listed in this medication guide.