Cymbalta (duloxetine) is an oral medication used primarily to treat major depressive disorder and generalized anxiety disorder. It has also been used to treat the chronic pain disorder fibromyalgia, pain from diabetic nerve damage, and chronic pain from osteoarthritis, musculoskeletal pain, and lower back pain. It is part of a class of medications called selective serotonin and norepinephrine reuptake inhibitors (SNRIs). It works by increasing the levels of serotonin and norepinephrine in the brain, two neurotransmitter chemicals that play an important role in maintaining mood and pain signals in the brain.

It is believed that a possible cause of depression is a low amount of the neurotransmitters serotonin and norepinephrine. In the brain, the space between where two neurons meet to communicate is called a synapse, and the synapse is where serotonin and norepinephrine are used to communicate between neurons. In depression, people may not have enough serotonin or norepinephrine in their brain. Normally after a chemical message is sent between neurons, the neurotransmitters are reabsorbed by the sending neuron (presynaptic neuron). A selective serotonin-norepinephrine reuptake inhibitor will bind to the presynaptic neuron and prevent it from absorbing the serotonin and norepinephrine, and leaving the neurotransmitters active in the synapse, and improving mood.