If you’ve had surgery to remove your thyroid gland and/or radioactive iodine therapy, your body may no longer make the thyroid hormones it used to make. You will likely be prescribed thyroid hormone therapy, which is usually given in the form of pills. These pills replace your lost hormones. Thyroid hormones are important because they help the body work properly.
The pituitary gland in your brain controls the thyroid. If the pituitary senses that thyroid levels are low, it will make a hormone called thyroid-stimulating hormone (TSH). This hormone normally stimulates the thyroid gland to make as much of its hormones as the body needs. TSH is also known to promote the growth of the thyroid gland and possibly promotes the growth of thyroid cancer cells. Therefore, keeping TSH low after you have had your thyroid removed due to cancer, may prevent some thyroid cancers from returning.
Conversely, if the pituitary senses that thyroid hormone levels are increased, it will not make very much TSH. Some studies have shown that people who had thyroid cancer treatment generally do better when the amount of TSH in their blood is low. So in people with thyroid cancer, a balanced amount of hormone pills are given to help the body work properly, and to keep TSH levels low.
People on thyroid hormone therapy need regular blood checks to avoid taking too little hormone (which would result in hypothyroidism) or taking too much hormone (which would result in hyperthyroidism). Signs of hypothyroidism include low energy, fatigue, sleepiness, weight gain, feeling cold all the time, hair loss, and dryness of the skin. Hyperthyroidism may cause nervousness, shaking, weight loss without dieting, diarrhea, rapid heartbeat, and excessive sweating. Over time, it may also lead to thinning of the bones (osteoporosis).