Eligible subjects will receive MRIs during the screening period, during the placebo period, during the NYX-2925 PO QD period. Safety assessments will be conducted and adverse events will be collected during the study. Daily pain scores and other fibromyalgia scales will be collected during the study. Daily pain scores and other fibromyalgia scales will be collected for exploratory analysis. During the follow-up period, an optional MRI will be completed for consenting subjects in order to evaluate duration of effect.