Final answer:
Milnacipran is the FDA-approved medication for treating fibromyalgia.
Step-by-step explanation:
The FDA-approved medication for treating fibromyalgia is Milnacipran. It is a selective serotonin and norepinephrine reuptake inhibitor (SNRI) that helps to reduce pain and improve physical function in patients with fibromyalgia. Other medications mentioned in the options, such as Citalopram, Escitalopram, Fluoxetine, and Gabapentin, are not specifically approved by the FDA for treating fibromyalgia.