Patient description: The patient is a 33-year-old woman complained of fatigue, weight gain and abnormal spotting between menses. No hirsutism or nipple discharge was detected. Her BMI was 34. Her lab results were remarkable for high TSH level (13 mU/L) and low free T4 level (0.2 ng/dl). Her anti-TPO levels were extremely high (120 IU/ml). She was diagnosed with Hashimoto's thyroiditis. Her aunt, brother and mother have the same disease. After starting 250 mcg Levothyroxine per day, her symptoms improved significantly and her periods are normal. She is still overweight with BMI of 31. Her most recent thyroid profile revealed all results except for anti-TPO within the normal range: TSH: 2.35 mU/L Free T4: 2.7 ng/dl Anti-TPO: 75 IU/ml

Clinical trial eligibility criteria: eligible ages (years): 18.0-99.0,  Malignant Struma Ovarii Papillary Thyroid Cancer Hurthle Cell Thyroid Cancer Follicular Thyroid Cancer Tall Cell Variant Thyroid Cancer Subjects will be adult volunteers older than age 18 who underwent total thyroidectomy for the treatment of differentiated thyroid cancer, previously undergone radioactive iodine ablation of the thyroid gland remnant, with clinical indication for withdrawal from thyroid hormone replacement therapy in preparation for nuclear medicine imaging or therapeutic procedures with radioactive iodine. The patient population will be recruited from the participants in the 77-DK-0096 natural history protocol: Studies on Thyroid Nodules and Thyroid Cancer , PI Dr.Joanna Klubo-Gwiezdzinska and from the 10-C-0102 natural history protocol: Clinical and Genetic Studies in Familial Non-Medullary Thyroid Cancer , PI Electron Kebebew  Significant thyroid residual greater than 5 gm as measure by ultrasound or greater than 5 percent uptake at 24 H on (123) I pre-treatment thyroid scan. 2. Renal insufficiency or estimated creatinine clearance less than or equal to 60 mL/min/1.73M(2) BSA by MDRD equation before thyroid hormone withdrawal. 3. Liver disease or ALT >2.5 times the upper laboratory reference limit. 4. Pharmacologic therapy for the treatment of psychiatric conditions. 5. History of, and/or current coronary artery disease. 6. Current history or symptoms compatible with psychosis or major depression (including history of hospitalization for depression, history of attempted suicide, history of suicidal ideation). Use of antipsychotic medications. 7. History of drug or alcohol abuse within the last year; current use of illicit drugs or alcohol abuse (CAGE>3). 8. Pregnancy (women of child-bearing potential must have a negative pregnancy test prior to inclusion) or use of hormonal contraceptives. 9. Known allergy to L-T3. 10. Current use of prescription medication or certain non-prescription medications and dietary supplements known to affect thyroid function and/or metabolism, or alter the pharmacokinetics of L-T3. 11. Inability or unwillingness to follow the low-iodine, metabolic diet or non-compliance to the L-T3 administration regimen. 12. The presence of persistent diarrhea or malabsorption syndromes that would interfere with the patient s ability to adequately absorb drugs. 13. Inability to obtain venous access for sample collection, or basal hemoglobin of less than or equal to 10 g/dL. 14. Low functional status (ECOG Performance Status > 2)