Cymbalta, the brandname form of duloxetine, is a prescription medicine used to treat depression, generalized anxiety disorder, diabetic peripheral neuropathic pain, fibromyalgia, and chronic musculoskeletal pain. Cymbalta is in a group of medications called serotonin norepinephrine reuptake inhibitors. These work by increasing the amount of serotonin and norepinephrine in the brain to promote mental balance and by stopping the movement of pain signals to the brain. This medication comes in capsule form and is taken once or twice daily, with or without food. Common side effects include nausea, dry mouth, and sleepiness. Do not.