Cymbalta (duloxetine hydrochloride) is a prescription medication used for such conditions as neuropathic pain, fibromyalgia (a rheumatoid disorder characterized by muscle pain and headaches), generalized anxiety disorder and depression. It’s not known exactly how this drug works to treat nerve pain, but it is thought it blocks pain signals in the brain or spinal cord. Headache, dry mouth, nausea, dizziness and drowsiness are the side effects you are likely to experience when taking Cymbalta. If these side effects persist or become bothersome they need to be reported to your health care provider.