Interferons are naturally occurring proteins that regulate immune function and inflammatory processes. These properties have led to the development of specific interferon molecules for the treatment of malignancy, hepatitis or multiple sclerosis. As many types of thyroid disease, particularly Hashimoto's disease and Grave's disease have an autoimmune basis, drugs such as interferon that produce effects on the immune system may also affect the course of autoimmune thyroid disease. Patients with thyroid antibodies are at higher risk of developing interferon-associated thyroid dysfunction, and this risk persists in antibody positive patients even after completion of interferon therapy. See Long-term outcome of interferon-alpha-induced thyroid autoimmunity and prognostic influence of thyroid autoantibody pattern at the end of treatment. J Clin Endocrinol Metab. 2001 May;86(5):1925-9. The development of interferon-associated thyroid disease does not seem to be related to the dose of interferon administered or the efficacy of therapy. See Thyroid dysfunction during treatment of chronic hepatitis C with interferon alpha: no association with either interferon dosage or efficacy of therapy. J Intern Med. 2002 May;251(5):400-406.

Interferon beta has been used for the treatment of multiple sclerosis. In some studies, interferon beta has been associated with the development of both hypo and hyperthyroidism in about one third of all patients receiving the drug Eur J Endocrinol 1999 Oct;141(4):325-31 Effect of 1-year treatment with interferon-beta1Effect of 1-year treatment with interferon-beta1b on thyroid function and autoimmunity in patients with multiple sclerosis. Long-term interferon beta-1b therapy for MS: is routine thyroid assessment always useful? Neurology 2000 Aug 22;55(4):549-52.

Interferon alpha has been used to treat patients with cancer and patients with hepatitis C. Interferon alpha has also been associated with the development of thyroid inflammation, and either hypo or hypothyroidism which commonly improves following discontinuation of interferon therapy. Arch Intern Med 1998 Jul 13;158(13):1445-8 Increased risk of autoimmune thyroid disease in hepatitis C vs hepatitis B before, during, and after discontinuing interferon therapy and Thyrotoxicosis induced by alpha-interferon therapy in chronic viral hepatitis. Clin Endocrinol (Oxf). 2002 Jun;56(6):793-8 and Incidence of thyroid dysfunction during interferon alfa-2b and ribavirin therapy in men with chronic hepatitis C: a prospective cohort study. Arch Intern Med. 2004 Nov 22;164(21):2371-6. and Thyroid dysfunction in patients with chronic hepatitis C receiving a combined therapy of interferon and ribavirin: Incidence, associated factors and prognosis.
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Patients receiving interferon therapy should have their thyroid function monitored prior to and periodically during the course of interferon treatment.