Gabapentin in Fibromyalgia Trial (GIFT)

Inclusion Criteria: * Primary fibromyalgia as defined by the American College of Rheumatology (ACR) * Score greater than 4 on the average pain item of the BPI at screening * Ability to understand and cooperate with study procedures * Acceptable methods of contraception Exclusion Criteria: * Unwillingness or inability to provide written informed consent. * Lifetime history of psychosis, hypomania or mania, epilepsy, or dementia * History of seizures or status epilepticus * DSM-IV diagnosis of alcohol or substance dependence with the exception of nicotine dependence within 6 months prior to screening visit * A positive urine drug screen for any substances of abuse or excluded medication. (NOTE: If the participant has a positive drug screen at Visit 1 for an excluded medication that may not have had an adequate wash-out period, a retest may be performed prior to Visit 2. If the retest is positive, the participant will be excluded.) * Serious suicide risk * Treatment refractory in the opinion of study official * Pregnant or breastfeeding * Clinically unstable medical or psychiatric condition that could interfere with the absorption, metabolism, excretion, or safety of gabapentin or interfere with the assessment of disease severity * Thyroid-stimulating hormone (TSH) concentrations outside the range of 0.30-8.0 UlU/mL. (NOTE: Participants who have been on a stable dose of thyroid supplementation for at least the past 3 months, have medically appropriate TSH values, and are clinically euthyroid may participate in the study.) * Any screening laboratory assay that is outside of the local laboratories' normal range by more than 20% or is deemed to be a clinically significant abnormality by the investigator, with the exception of liver function tests (AST, ALT, alkaline phosphatase) which must be within 1.5 X upper limit of normal * Inability to exclude traumatic injury, regional or structural rheumatic disease, or infectious arthropathy as the etiology of their relevant symptoms and that would interfere with interpretation of outcome measures (e.g., osteoarthritis, bursitis, tendonitis) * History of an autoimmune disease or inflammatory arthritis, such as systemic lupus erythematosis (SLE) or rheumatoid arthritis (RA). * An abnormal Westergren erythrocyte sedimentation rate (e.g., ESR \> 40 mm/min) * An abnormal antinuclear antibody (ANA \> 1:160) or rheumatoid factor (RF \>15 IU/ml) * Treatment with a monoamine oxidase inhibitor, tricyclic, SSRI antidepressant (with the exception of fluoxetine), or lithium within 2 weeks prior to beginning study medication * Treatment with fluoxetine within 30 days prior to beginning study medication * Treatment with analgesic medication (with the exception of acetaminophen and over-the-counter NSAIDs) within 1 week prior to beginning study medication * Treatment with any other excluded medications that cannot be discontinued at the screening visit (see Table 2 for a list of excluded medications) * Previous treatment with gabapentin * Previous treatment with pregabalin * Treatment with any other investigational medications within 30 days prior to screening