I have been treated for about 2 years with T4 (Cytomel) and would like to direct you to
www.drlowe.com for a good explanation. My thyroid test always come out "normal" but the theory is that while my body produces enough thyroid I do not absorb the T4 correctly. There is also some good information in the April 2004 Fibromyalgia Network newsletter (pg 10-13). The symptoms of hypothyroidism match many of those for I have for Fibro (and some I have but didn't connect to the Fibro) including exhaustion, impaired thinking, difficulty staying warm, low body temp, weight gain (despite reduced appetite), constipation (slow digestion), dry skin/acne prone, dry brittle hair (mine was falling out), low blood pressure, and high cholesterol (from the Fibromyalgia Network article). You do need to be careful and monitor the dose closely, making changes when necessary.
Just thought I would weigh in on this one, although it is still a theory, it is helping me!
Christina Seeger, Portland, Oregon