Thyroid drugs (thyroid hormones) are used to supplement low thyroid levels in people with hypothyroidism.

Hypothyroidism is a condition in which the thyroid gland does not produce enough thyroid hormones to meet the needs of the body. Doctors may use the term “an underactive thyroid gland” to describe hypothyroidism.

Our thyroid gland is a butterfly-shaped gland that is located just below the Adam’s apple, along the front of the windpipe. Even though thyroid hormones are made in the thyroid gland, the production of these hormones is regulated by another hormone, called thyroid stimulating hormone (TSH), which is made by the pituitary gland (a pea-shaped organ found at the base of the brain). If thyroid hormone levels are low, then our metabolism and many other body functions slow down.

Another condition, called hyperthyroidism, is when the thyroid produces too much thyroid hormone. Although hyperthyroidism seems to be the opposite of hypothyroidism, the link between them is complex, and one can lead to the other in certain circumstances.

What are thyroid drugs used for?

Thyroid drugs are used to treat hypothyroidism, also referred to as an underactive thyroid.

Even though the thyroid produces two hormones, T3 and T4, T4 is most commonly prescribed to treat hypothyroidism.

The only way to test for hypothyroidism is with a blood test, as symptoms vary significantly between people and are similar to several other conditions.

Symptoms of hypothyroidism include:

• Cold intolerance
• Constipation
• Decreased sweating
• Dry skin
• Frequent urinary and respiratory tract infections
• Heavy periods
• Joint and muscle pain, cramps, or weakness; slowed movements
• Loss of sex drive
• Puffy face, feet, and hands
• Sleeplessness (insomnia)
• Slowed heart rate
• Thin brittle hair or fingernails
• Tiredness and fatigue
• Weight gain.

If hypothyroidism develops in children or teenagers it may affect their growth; interfere with learning and brain development; and delay tooth development and puberty.

What are the differences between thyroid drugs?

Thyroid hormone preparations can be divided into two categories:

• Natural preparations derived from animal thyroid
• Synthetic preparations manufactured in a laboratory.

Natural preparations include desiccated thyroid and thyroglobulin.

The most common medication used for supplementation is synthetic thyroxine, also called levothyroxine. This is identical to the T4 hormone. T4 is converted into T3 in the body.

Liothyronine (T3, also called triiodothyronine) is another thyroid hormone that may be prescribed to people who are unable to properly convert T4 into T3.

Liotrix was a combination of levothyroxine (T4) and liothyronine (T3) in a 4:1 ratio. It has been discontinued. 

It is important that levothyroxine is taken on an empty stomach at least 30 to 60 minutes before breakfast to ensure that it is absorbed properly. It should be taken with a big glass of water, and spaced apart by at least four hours from antacids or supplements such as calcium or iron.

Are thyroid drugs safe?

Thyroid medicines are safe when taken at the recommended dose and prescribed by a doctor. You must ONLY take what your doctor recommends. The correct dosage for you is based on your age, health, current natural thyroid hormone levels, and weight.

When you first start treatment for hypothyroidism, your doctor will regularly monitor the levels of different thyroid hormones in your blood to determine if your dosage of thyroid medication needs adjusting. Once the correct dosage has been established for you, the frequency of these blood tests will decrease. Thyroid drugs are generally taken for life.

It will take a few months for your thyroid levels to get back to normal but as long as you are taking your thyroid drugs as prescribed, then you should not have many side effects. Side effects generally happen because you are taking too much thyroid hormone.

Thyroid hormones should NEVER be taken by people without thyroid problems to treat obesity or for weight loss. Some fatalities have occurred when they have been used if these drugs are taken in large dosages for this indication.

Be aware that some supplements marketed as supporting thyroid health may actually contain undisclosed thyroid hormones. Taking these in addition to your thyroid medications may cause toxicity. Thyroid drugs have also been serendipitously added to supplements labeled as only containing animal tissue or herbs such as ashwagandha, guggul, and Coleus forskohlii. Even seaweed-containing products, such as kelp, contain high levels of iodine which can interfere with thyroid function. If you are taking thyroid drugs, always talk with your doctor before taking any supplement.

Also, talk to your doctor about your diet. Some people with hypothyroidism are particularly sensitive to the effects of iodine, and it may trigger or worsen hypothyroidism. In addition, high fiber diets and certain types of foods such as soy or cruciferous vegetables may affect how your body responds to thyroid drugs.

What are the side effects of thyroid drugs?

Thyroid drugs don’t tend to cause side effects if taken at the right dose. Side effects are an indication that you may be taking too much thyroid hormone and may include:

• A fast heartbeat
• Difficulty sleeping
• Dull, lifeless, or brittle hair
• Heat sensitivity
• Hunger
• Nervousness or anxiety
• Shakiness
• Sweating
• Tiredness
• Weight loss.

If you develop any of these side effects talk to your doctor about a blood test to check your thyroid hormone levels.