•Males and Females, 18-50 years of age.
•Chronic (≥ 6 weeks) idiopathic urticaria.
•High (above normal range) levels of antithyroid antibodies (TPO-Ab, TG-Ab).
•Either euthyroid or with “subclinical hypothyroidism” defined as having normal free T4 and TSH <10 mIU/L.
•Failure of a trial of recommended doses of antihistamines for 2 weeks.
•Coexisting diseases which limit ability to tolerate minimally excess dosages of thyroxine (i.e. cardiac disease).
•Prescribed medications whose efficacy could be altered by thyroid function (digoxin, warfarin, seizure medications).
•Patients with TSH < 1.0 mIU/L or ≥ 10 mIU/L on initial screening.
•Treatment with thyroid hormone in past 3 months.
•Use of immunosuppressive drugs (e.g. prednisone, cyclosporine, anti-IgE, imuran, etc.) within the last 1 month.
•Age >50 years.