This is an open-label study of DS-5565 in subjects who either completed participation in a preceding Phase 3 study of DS-5565 in fibromyalgia (FM); i.e. DS5565-A-E309, DS5565-A-E310, or DS5565-A-E311 or are de novo subjects. Eligible subjects will be assigned to receive open-label DS-5565 for 52 weeks. All subjects will receive DS-5565 15 mg once daily (QD) for the first three weeks of the treatment period. After three weeks, subjects may be titrated to 15 mg twice daily (BID) based on protocol-specified criteria.