To evaluate the safety and to determine the efficacy of D-ribose for the amelioration of fatigue in subjects with fibromyalgia. This is a phase IIa, randomized, double-blind, placebo-controlled, multi-center, multiple dose study of D-ribose versus placebo administered at doses of 5 g three times a day (TID) over a 12-week period to subjects who are experiencing fatigue associated with a diagnosis of fibromyalgia.

Major Inclusion Criteria:

• must have a diagnosis of primary fibromyalgia, as defined by the 1990 American College of Rheumatology (ACR) Criteria for the Classification of Fibromyalgia made at least 6 weeks prior to the Pretreatment Screening Visit;
• must have a score of ≥5 on the Subject's Assessment of Fatigue 11-point numerical rating scale (NRS) at the Pretreatment Screening and Baseline Visits;
• if taking acetaminophen or other non-opioid analgesics, NSAIDs, fibromyalgia medications, medications to induce sleep, or prednisone ≤ 10 mg (or equivalent dose of other glucocorticoids), must be on stable dose(s) for at least 4 weeks prior to the baseline visit;
• must have discontinued any ribose-containing products (including foods, drinks, and supplements) at least 4 weeks prior to the Pretreatment Baseline Visit.

Major Exclusion Criteria:

• current major depressive episode (MDE);
• has been diagnosed with any autoimmune disease;
• has been diagnosed with type I or type II diabetes;
• has a history of cancer, other than basal cell carcinoma, stage 1 squamous cell carcinoma or cervical carcinoma in situ, that has not been in remission for at least five years prior to the Pretreatment Screening Visit;
• has been diagnosed with chronic fatigue syndrome.