Duloxetine is a serotonin-norepinephrine reuptake inhibitor (SNRI). It increases the levels of serotonin and norepinephrine in the brain by blocking their reuptake. These neurotransmitters play a key role in regulating mood and pain perception. Duloxetine is primarily used to treat depression, anxiety, and chronic pain conditions like fibromyalgia and diabetic neuropathy.