Will I put on weight with thyroxine medication after thyroidectomy?
The thyroid gland has only one function, which is to manufacture and secrete the thyroid hormones T3 and T4. These are the master hormones which control the body’s metabolic activity. The secretion of thyroid hormones is adjusted by another hormone secreted by the pituitary gland called Thyroid Stimulating Hormone (TSH) via a negative feedback cycle. An explanation of the physiology of the thyroid can be found in a book chapter written by Professor Delbridge (see below). Measurement of TSH levels in the blood is a very sensitive indicator of whether or not the body is receiving the correct amount of thyroxine.
If the thyroid gland needs to be removed either because of thyroid cancer, Graves’ disease causing overactivity of the gland, or a multinodular goitre causing pressure symptoms, then normal hormone levels are readily achieved after surgery by replacement therapy which simply involves taking a tablet once a day. The correct dose of thyroxine is established with blood tests (thyroid function tests) and, provided the correct dose is taken regularly every day then the body’s metabolic activity will be absolutely normal and you will not put on weight. Indeed weight management with exercise and diet may be more straightforward after surgery as hormone levels will often be more stable than with a diseased gland. In the vast majority of cases, patients who encounter difficulties with thyroid replacement therapy are non-compliant (i.e. they forget to take their tablets every few days) and this will play havoc with the activity of TSH which takes weeks for the pituitary gland to re-set. Other reasons for difficulty include: taking medication with food or at different times of the day; leaving medication out in the hot sun; frequent changes of dose depending upon how you feel on any particular day.
Replacement therapy is normally provided in the form of a tablet of synthetic thyroxine taken once a day. This is identical to the T4 hormone naturally produced by the body and the two brands available in Australia (Eutroxsig and Oroxine) are identical. The active form of thyroid hormone is T3, however that is produced by the body converting T4 to T3 at a cellular level. Some patients prefer a mix of T4 and T3 which can be dispensed by compounding pharmacists (see PP), as they say they feel better on combination therapy, however there is no scientific data supporting that view. The vast majority of patients feel perfectly well and normal on standard thyroxine replacement therapy.