Patient instructed Duloxetine is used to treat major depressive disorder in adults. It is also used to treat general generalized anxiety disorder. It is also used in adults to treat fibromyalgia (a chronic pain disorder), or chronic muscle or joint pain (such as low back pain and osteoarthritis pain). Take duloxetine exactly as prescribed by your doctor. Follow all directions on your prescription label. Do not take this medicine in larger or smaller amounts or for longer than recommended. You may take duloxetine with or without food. Do not crush, chew, break, or open an extended-release capsule. Swallow it whole.