Fibromyalgia (FM) is a nonarticular rheumatological syndrome associated with diverse clinical and psychological features. One of the major complaints in FM is reduced pain tolerance, especially in tender points (TP) for which patients derive significant benefit from nonsteroidal antiinflammatory drugs or corticosteroids. Patients with FM also have altered reactivity of the hypothalamic pituitary adrenal (HPA) axis where the predominant feature is reduced containment of the stress response system through diminished adrenocortical output and feedback resistance. Our results show that mud packs together with antidepressant treatment are able to influence the HPA axis, stimulating increased levels of adrenocorticotropic hormone, cortisol and beta-endorphin serum levels. The discharge of corticoids in the blood and the increase in beta-endorphin serum levels are followed by a reduction in pain symptoms, which is closely related to an improvement in disability, depression and quality of life. It seems that the synergic association between a pharmacological treatment (trazodone) and mud packs acts by helping the physiological responses to achieve homeostasis and to rebalance the stress response system. To clarify and optimize the effectiveness of this synergic association, studies involving a larger number of FM patients and a different pharmacological treatment are needed.