Thyroid Replacement Hormones

Thyroid replacement hormones are medications used to treat hypothyroidism, a condition in which the production of thyroid hormone in the body is low. Thyroid hormones increase cellular metabolism responsible for growth, development of tissues, maintenance of brain function, body temperature regulation, and other processes. Low levels of thyroid hormones can cause problems due to their various activities. The thyroid gland in the lower neck produces two main hormones: thyroxine (T4) and triiodothyronine (T3). T3 is responsible for most of the biological effects. T4 is converted to T3 in the blood. Thyroid hormones can be natural or synthetic. Natural hormones are derived from beef or pork, while synthetic hormones are man-made.

Examples of Thyroid Replacement Hormones

The following are thyroid replacement hormones available in the United States:

• levothyroxine sodium (Levothroid, Levoxyl, Synthroid, Tirosint, Unithroid)
• liothyronine sodium (Cytomel, Triostat)
• liotrix (Thyrolar)

Uses for Thyroid Replacement Hormones

Thyroid replacement hormones are used to treat low production of thyroid hormone (hypothyroidism) and myxedema caused by prolonged hypothyroidism. They also prevent thyroid hormone release from cancerous thyroid nodules and treat thyroid cancers. Thyroid replacement hormones are used to manage thyrotoxicosis, a condition with high levels of thyroid hormones resulting from over-active thyroid glands. They also treat goiters resulting from thyrotoxicosis.

Differences Among Thyroid Replacement Hormones

There is conflicting evidence regarding which hormone replacement therapy is best. The American Association of Clinical Endocrinologists recommends synthetic T4 levothyroxine for hypothyroidism. There is variability between generic and brand name preparations. T3 and T4/T3 formulations have variability as well. Thyroid extracts from animal sources are no longer available in the United States. Some studies suggest a combination of T4/T3 therapy may have benefits in cognitive performance and mood.

Side Effects of Thyroid Replacement Hormones

Thyroid replacement hormones are generally well tolerated. Symptoms during treatment may indicate elevated levels of thyroid hormones and hyperthyroidism. Symptoms may include chest pain, increased heart rate, excessive sweating, heat intolerance, nervousness, headache, insomnia, diarrhea, vomiting, weight loss, fever, and irregular menstrual cycles.

Drug Interactions with Thyroid Replacement Hormones

Thyroid replacement hormones should be used cautiously in people with diabetes. Blood thinners may be affected by thyroid replacement hormones, and beta blockers may be less effective. Dose adjustments may be necessary for medications such as digoxin and theophylline when transitioning from hypothyroidism to a normal state. Calcium carbonate, ferrous sulphate, cholestyramine, and colestipol can decrease the effectiveness of thyroid replacement hormones.

Related Disease Conditions

Hypothyroidism

Hypothyroidism is a condition in which thyroid hormone production is below normal. Symptoms include constipation, memory loss, hair loss, and depression. Treatment depends on the cause.

Thyroid Disorders

Thyroid disorders include hypothyroidism, hyperthyroidism, goiters, thyroid nodules, and thyroid cancer. Symptoms vary by condition. Diagnosis is made with tests, scans, ultrasound, or biopsy. Treatments can include medication or surgery.

Hashimoto’s Thyroiditis

Hashimoto’s thyroiditis is an autoimmune disorder causing inflammation of the thyroid gland. It is the most common cause of hypothyroidism in the US. Symptoms include fatigue, weight gain, feeling cold, dry skin, difficulty swallowing, muscle cramps, mood changes, and depression. Treatment involves thyroid hormone replacement therapy.

Causes and Symptoms of Hormonal Imbalances in Women

The main causes of hormonal imbalances are issues with the thyroid, stress, and eating disorders. Symptoms include irregular periods, low sex drive, unexplained weight gain, and mood swings. Treatment involves addressing the underlying cause, diet changes, exercise, and stress management.

Effect of Hormonal Imbalance on Pregnancy

Hormonal imbalance is a common issue that can affect pregnancy. Learn about the signs, diagnosis, and treatment.

Role of the Hypothalamus

The hypothalamus is a part of the midbrain that regulates all hormonal functions in the body. It links the nervous system to the endocrine system through the pituitary gland.

Warning Signs of Thyroid Cancer

Thyroid cancer arises from the cells of the thyroid gland. Warning signs include a lump in the neck, trouble swallowing or breathing, voice changes, cough, weight loss, and palpitations.

Effects of Thyroid Cancer on the Body

Thyroid cancer arises from the cells of the thyroid gland. Symptoms may include a lump in the neck, trouble swallowing or breathing, voice changes, cough, weight loss, and palpitations.