['pain associated with fibromyalgia']
['ds-5565', 'pregabalin', 'placebo tablet', 'placebo capsule']

        Inclusion Criteria:

          -  Age ≥ 18 years

          -  Able to give written informed consent

          -  Able to complete participant-reported questionnaires per the investigator's judgment

          -  At screening, participants must meet the 1990 American College of Rheumatology (ACR)
             criteria for fibromyalgia (FM), i.e. widespread pain present for at least 3 months and
             pain in at least 11 of 18 specific tender point sites. In addition, the 2010 ACR
             criteria must be met:

          -  Widespread pain index (WPI) ≥ 7 and symptom severity (SS) scale score ≥ 5, or WPI 3 to
             6 and SS scale score ≥ 9

          -  Symptoms have been present at a similar level for at least 3 months

          -  The subject does not have a disorder that would otherwise explain the pain

          -  ADPS of ≥ 4 on the 11-point numeric rating scale (NRS) over the past 7 days prior to
             randomization (based on completion of at least 4 daily pain diaries during the 7-day
             baseline period prior to randomization)

          -  Subject must have documented evidence of a fundoscopic examination (with pupil
             dilation) within 12 months prior to screening or at screening.

          -  Women of child-bearing potential (WOCBP) must be using an adequate method of
             contraception to avoid pregnancy during the study and for 4 weeks after study
             completion.

        Exclusion Criteria:

          -  Clinically significant unstable neurologic, psychiatric, ophthalmologic,
             hepatobiliary, respiratory, or hematologic illness or unstable cardiovascular disease
             (e.g. severe hypotension, uncontrolled cardiac arrhythmia, or myocardial infarction)
             or any other concurrent disease within 12 months prior to screening that in the
             opinion of the investigator would interfere with study participation or assessment of
             safety and tolerability

          -  Anticipation of initiation or significant change to normal daily exercise routines or
             need for ongoing use of concomitant medications or non-pharmacological pain management
             techniques that may confound assessments of efficacy and/or safety

          -  Unable to undergo pre-study washout of prohibited concomitant medications

          -  Subjects who are at risk of suicide as defined by their responses to the
             Columbia-Suicide Severity Rating Scale (C-SSRS) or in the opinion of the investigator.
             Note: Patients answering "yes" to any of the questions about active suicidal
             ideation/intent/behaviors occurring within the past 12 months must be excluded (C-SSRS
             Suicide Ideation section - Questions 3, 4, or 5; C-SSRS Suicidal Behavior section, any
             of the suicide behaviors questions). Such patients should be referred immediately to a
             mental health professional for appropriate evaluation.

          -  Current severe or uncontrolled major depressive disorder or anxiety disorders as
             assessed by the Mini-international Neuropsychiatric Interview (MINI) mild to moderate
             major depression or anxiety disorders are permitted provided that the investigator
             assesses the patient as clinically stable and appropriate for entry into the study.

          -  Any diagnosis of lifetime bipolar disorder or psychotic disorder

          -  Participants with pain due to other conditions (e.g. diabetic peripheral neuropathic
             pain or post-herpetic neuralgia) that in the opinion of the investigator, would
             confound assessment or self-evaluation of the pain associated with FM.

          -  Participants with pain due to any widespread inflammatory musculoskeletal disorder
             (e.g. rheumatoid arthritis, lupus) or widespread rheumatic disease other than FM.

          -  Abuse or dependence of prescription medications, street drugs, or alcohol within the
             last 1 year

          -  Any history of a malignancy other than basal cell carcinoma within the past 5 years

          -  A diagnosis of untreated sleep apnea or initiation of treatment for sleep apnea within
             the past 3 months

          -  Pregnancy or breast-feeding, or intent to become pregnant during the study period

          -  Participant is currently enrolled in or has not yet completed at least 30 days since
             ending another investigational device or drug study or is receiving other
             investigational agents.

          -  Known hypersensitivity to alpha2-delta (α2δ) ligands or other components of the study
             medications. Note: Prior exposure to DS-5565 is allowed, as long as hypersensitivity
             to DS-5565 was not observed.

          -  Participants who are unlikely to comply with the protocol (e.g. uncooperative
             attitude, inability to return for subsequent visits) and/or otherwise considered by
             the investigator to be unlikely to complete the study.

          -  Abnormal investigative tests (i.e. electrocardiograms [ECGs]) and laboratory values
             judged by the investigator to be clinically significant at screening, with particular
             focus on: a. Abnormal renal function defined as calculated creatinine clearance (CrCl)
             < 60 mL/min determined by the central laboratory using the modified Cockcroft-Gault
             equation; blood urea nitrogen> 1.5 × upper limit of normal (ULN); creatine kinase >
             3.0 × ULN; serum creatinine > 1.6 mg/dL (> 141.4 μmol/L); b. Abnormal liver function
             defined as aspartate aminotransferase (AST) > 2.0 × ULN, alanine aminotransferase
             (ALT) > 2.0 × ULN; alkaline phosphatase > 1.5 × ULN; total bilirubin> 1.2 × ULN. If a
             subject has total bilirubin > 1.2 ULN, unconjugated and conjugated bilirubin fractions
             should be analyzed and only participants documented to have Gilbert's syndrome may be
             enrolled.
      