Taking thyroid hormone is different from taking other medications because its job is to replace a hormone that is missing.

Many people have a thyroid gland that cannot make enough thyroid hormone for the body’s needs. This is called Hypothyroidism and may be caused by a nonfunctioning thyroid gland (for example Hashimoto’s disease), by the destruction of the thyroid gland by surgery or radiation treatment, or by a non-functioning pituitary gland. Hypothyroidism is the most common reason for needing thyroid hormone replacement.

The goal of thyroid hormone treatment is to closely replicate normal thyroid functioning. Pure, synthetic thyroxine (T4) works in the same way as a patient’s own thyroid hormone would. Thyroid hormone is necessary for the health of all the cells in the body.

Therefore, taking thyroid hormone is different from taking other medications, because its job is to replace a hormone that is missing. The only safety concerns about taking thyroid hormone are taking too much or too little. Your thyroid function will be monitored by your physician to make sure this does not happen.

What is the thyroid gland?

The thyroid gland is a butterfly-shaped endocrine gland that is normally located in the lower front of the neck. The thyroid’s job is to make thyroid hormones, which are secreted into the blood and then carried to every tissue in the body.

Thyroid hormone helps the body use energy, stay warm, and keep the brain, heart, muscles, and other organs working as they should.

How is the dose of thyroid hormone chosen?

When someone is first started on thyroid hormone the initial dose is carefully selected based on information such as a person’s weight, age, and other medical conditions. The dose will then need to be adjusted by a physician to keep the thyroid function normal.

The physician will make sure the thyroid hormone dose is correct by performing a physical examination and checking TSH levels.

There are several brand names of thyroid hormone available. Although these all contain the same synthetic T4, there are different inactive ingredients in each of the brand names. In general, it is best for you to stay on the same brand name.

If a change in the brand name is unavoidable, you should be sure your physician is aware of the change, so that your thyroid function can be rechecked. If your pharmacy plan changes your thyroid hormone to a generic preparation, it is important for you to inform your physician.

What about T3?

While most actions of thyroid hormone are most likely due to T3, most T3 in the body comes from the conversion of T4. The conversion of T4 to T3 is normal in hypothyroid patients. T3 has a very short life span in the body, while the life span of T4 is much longer, ensuring a steady supply of T3.

Preparation of synthetic T3 (Cytomel) is available. After taking a tablet of Cytomel there are very high levels of T3 for a short time, and then the levels fall off very rapidly. This means that T3 has to be taken several times each day, and even doing this does not smooth out the T3 levels properly.

In addition, it is impossible to avoid having too much thyroid hormone in the system soon after each dose of T3 is taken. High T3 levels can lead to unpleasant symptoms such as rapid heartbeat, insomnia, and anxiety.

High T3 levels also can harm the heart and the bones. Another concern with using T3 treatment is that the body is deprived of the ability to adjust the conversion of T4 to T3 to regulate the supply of T3 according to the body’s own needs. Thus, there is no indication for the use of T3 alone for the treatment of hypothyroidism.

What about combined T4 and T3 treatment?

Some hormone preparations containing both T4 and T3 are available in the United States (Thyrolar®). Combination T4/T3 preparations contain much more T3 than is usually produced naturally within the body. Because of this, they can have the same side effects as T3 given by itself. It is also given once a day, ignoring the short life span of T3 in the body.

There has been the interest in whether a combination of T4 and T3, with a lower amount of T3 given more than once a day, might result in better treatment of hypothyroidism, especially in those patients that do not feel completely normal on T4 alone.

In these cases, Cytomel (T3) is taken in addition to T4. A trial period of 3 – 6 months is reasonable to determine if combination T4 and T3 therapy will help.

Will thyroid hormone help me if I have hypothyroid symptoms but normal thyroid hormone levels?

Some people with normal thyroid blood tests have symptoms that are similar to symptoms of hypothyroidism. Several scientific studies have looked at whether T4 therapy would be of benefit to patients with symptoms that overlap with hypothyroid symptoms and normal thyroid function.

In all cases, there was no difference between T4 and a placebo (sugar pill) in improving symptoms or well-being.

A Medicine for Underactive Thyroid

Levothyroxine is a medicine used to treat an underactive thyroid gland (hypothyroidism).

The thyroid gland makes thyroid hormone which helps to control energy levels and growth. Levothyroxine is taken to replace the missing thyroid hormone.

Levothyroxine is only available on prescription. It comes as tablets or as a liquid that you drink.

Key facts

  1. Levothyroxine starts working straight away, but it may be several weeks before your symptoms start to improve.
  2. The most common side effects of levothyroxine are caused by taking a bigger dose than you need.
  3. A doctor can lower your dose to help reduce any side effects.
  4. Before you start taking levothyroxine, a doctor will do a blood test to see what dose you need.
  5. Once you start taking the medicine you’ll have regular blood tests to see how well it’s working.

Thyroid Hormone Suppression Therapy for Bening Nodules and Goiter

In the past, thyroid hormone suppression therapy was used to prevent benign thyroid nodules and enlarged thyroid glands from growing. More recent evidence has shown that this practice is not effective in regions of the world that have adequate iodine intake (such as the USA).

Moreover, excess thyroid hormone can increase the risk of heart rhythm problems and bone loss making the use of thyroxine for suppressing benign thyroid tissue more risky than beneficial in iodine-sufficient populations.

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