Thyroxine's Effect on Metabolism
Thyroxine is the main hormone produced by the thyroid gland and what controls the body's basal metabolic rate (BMR). A person's basal metabolic rate refers to the minimum number of calories he needs to survive in the absence of any activity. The higher the BMR, the more calories an individual's body burns and the faster the metabolism. According to the Vitamin and Supplements Guide, every cell in the body depends on thyroid hormones for proper metabolism. The iodine containing hormone controls neural development as well as releasing fats from most of the fat cells controlling metabolism and affecting growth. A lack of thyroxine contributes to growth disorders in children, leading to cretinism and hypothyroidism. Too much thyroxine causes a BMR that is too high. This leads to Graves' disease, a condition pertaining to an overactive thyroid.
Weight Loss, Metabolism and Side Effects
Too much thyroid hormone in the bloodstream can create extremes in body weight due to differences in basal metabolic rate. Certain people who don't have a thyroxine deficiency or hypothyroidism have tried using the hormone in an effort to increase their metabolism to lose weight. WomenAnswers.org advises that "Taken...in excess it is potentially cardiotoxic (damaging to the heart), causes angina, cardiac arrhythmia's and palpitations. It will produce osteoporosis, muscle cramps, diarrhea, vomiting, tremors, excitability, insomnia, sweating and muscular weakness."
Thyroid Replacement Medicine
Fluctuations in thyroid levels and metabolism can be controlled with medications. By restoring normal metabolic activity from hypothyroidism or Graves' disease, with the use of thyroxine supplementation, body weight can be controlled for most people and BMR can be returned to its optimal levels. This hormone is designed to be used medically under the care of a doctor and is only available by prescription. If you think your metabolism is not normal and that thyroid tests may indicate an imbalance, see a doctor.