“My daughter has been advised Thyronorm 25mg. Will it be lifelong?”

Not quite enough information in your question to answer properly. Need to know something about what symptoms or abnormalities on exam were present that prompted the blood work for thyroid functions, exact results of the blood work for total T4, free T4, total T3, TSH levels and also for thyroid colloid and microsomal antibody results. Most common reason for hypothyroidism is a condition that is an autoimmune attack on the thyroid glands called Hashimoto's thyroiditis - so positive antibody results make this diagnosis if present. The thyroid gland can function normally but get enlarged, called a goiter. Sometimes there are cysts and sometimes there has been damage from chemotherapy or radiation therapy or even surgery; other times there are problems with the hypothalamus or pituitary thyroid controlling centers and this too can cause hypothyroidism. And in parts of the world where salt is not supplemented with iodine, iodine deficiency can interfere with thyroid function too. Some newborns are also born with abnormal thyroid glands for a variety of reasons but currently most states in USA do newborn blood screening and thyroid testing is included so this isn't missed as much as when there was no automatic screening done after birth. Once a proper specific diagnosis is made, then answering your question becomes easier and usually once hypothyroidism is diagnosed, thyroid hormone treatment with once-a-day pills is all that is needed. Some people need a little bit of T3 added to their T4 but most just need the thyroxine/levothyroxine once-a-day. The dose you described is actually 25 ugm not mg and this is a very small dose but depends on age and weight. Usually if there is hypothyroidism this is a permanent condition and doses need to be checked 3-4x/year during infancy, childhood and teenage years to adjust individual needs. Goal is to keep the total T4, free T4, total T3 and TSH levels all within normal limits for optimizing outcomes so followup blood work needs to be done 3-4x/year indefinitely to double check that doses are okay and/or any changes identified and treatment adjusted. Hope that gives you some information. The American Thyroid Association has some good information available on line too. Stuart Brink, MD Senior Endocrinologist, New England Diabetes & Endocrinology Center (NEDEC) c/o NEDEC, 196 Pleasant Street, Newton Centre MA 02459-1815, USA phone 1-781-572-4533, e-mail: stuartbrink@gmail.com

The thyroid gland is one of the very important hormone producing gland in the body. It makes thyroid hormone that controls our energy balance. But it doesn't function properly all the time for every body. In some people it makes less (under-active). In others it makes more (overactive).
When it is under-active (making less hormone), the person needs thyroid hormone replacement to mentain normal energy balance. The treatment could be with verious different medications, including synthroid, levothyroxine, levoxyl, armour thyroid, NP thyroid, Nature thyroid, thyronorm etc. So thyronorm is a treatment for under-active thyroid. Don't get confused with elevated TSH which is mostly a sign of low thyroid production.
Hypothyroidism (under-active thyroid) as in your daughter's case may resolve after a while of treatment. Some will continue to require treatment and some will resolve after a while of treatment. The same is also true for overactive thyroid condition in which about 25-30% will resolve in about 2 years of treatment.
Good luck

It depends on the reason why she was started on the medication.