I developed symptoms of hypothyroidism (coldness, dry skin, constipation) about 7 months after starting Rebif in 2002. My primary care doc. tested my TSH and T3 and T4 and sure enough, I had a severely sluggish thyroid.
Started synthroid in March of 2003 and now, after having a baby and changing meds to Betaseron, still need the synthroid. My neuro. routinely checks thyroid function when he checks my liver levels every 6 mos.
I should also state that I had been on the borderline of hypothyroidism before going on the meds, but had no symptoms. The interferon seemed to fry an already delicate thyroid function in my case.
Thanks for the question!