Study of Dose Adjustment From Levothyroxine to a New Levothyroxine Sodium Test Formulation

Inclusion Criteria: 1. (Near) total thyroidectomised patients. 2. Aged 18 years and older. 3. Stabilised on the same daily dose of L-Thyroxine Christiaens® during the last 6 weeks before inclusion in the study. 4. Written informed consent given. 5. Able and willing to comply with protocol requirements and to complete the study. Exclusion Criteria: 1. History of Graves' disease or positive TSH-receptor antibodies. 2. History of thyroid cancer requiring TSH suppression. 3. Medical procedures or treatments planned that could influence the thyroid hormone state of the patients during this trial. 4. Use of levothyroxine containing medicines provided by other brands to treat hypothyroidism. 5. Pregnant or planning pregnancy. Female patients of childbearing potential need to apply highly effective methods of birth control. 6. Participation in another trial in the past 6 weeks. 7. Exclusion criteria during the study are the occurrence of any serious adverse reaction, any laboratory or clinically relevant change in patient status, any change in smoking status, use of drugs non-authorized by the physician (to avoid relevant drug interactions) and lack of patient compliance with the study drug. (OR events not considered as exclusion criteria but to be documented in the case report form, as a possible explanation for change in lab parameters and/or dose switch).