The objective of this protocol is to evaluate if Dextromethorphan (DXM) reduces Fibromyalgia
(FM) pain. DXM is a drug found in several over-the-counter products, including cough
suppressants. The drug may reduce FM pain by suppressing inflammation in the central nervous
system. The investigators will be observing the effects of DXM on daily self-reported pain
measures in people with FM. If DXM reduces FM pain, it will provide important information
about the nature of FM pathophysiology.