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Thyroid Hormones

Thyroid -Stimulating Hormone (TSH)

TSH stimulates the thyroid to release T4 and T3 into your bloodstream. TSH comes from your hypothalamus.

Thyroxine (T4)

One of two major hormones made by the thyroid gland. Your thyroid mostly creates T4, which is an inactive hormone. T4 gets created into T3, which is more active. It helps to control the rate your body uses energy. 

Triiodothyronine (T3)

The other major hormone made by your thyroid gland which works with T4 to control the rate your body uses energy. 


Occurs when there is too much thyroid hormone. 


Occurs when there is not enough thyroid hormone.

Those with no thyroid or a poorly-functioning thyroid will have to rely on replacement thyroid hormones for the rest of their lives. Not taking your prescription can be fatal. Routine blood tests will be necessary to make sure your TSH is at an optimal level. For those wanting to get pregnant or who are already pregnant, your levels will need to be tested and your medication will probably need to be increased to give you extra thyroid hormones for you and your baby. Please consult with your doctor if wanting to or you become pregnant. 

If you rely on replacement thyroid hormones, here's why it's important to take your prescribed dosage:

If left untreated, hyperthyroidism may lead to serious heart problems and be life-threatening. If your body is always running on overtime, you may have abnormal heart beat, sudden cardiac arrest, or hypertension (high blood pressure). A thyroid storm is when your heart rate, blood pressure, and body temperature go to dangerous levels due to un- or under-treated hyperthyroidism.

If left untreated, hypothyroidism may lead to serious problems and could be fatal. Slow heart rate means your blood isn't moving to vital parts of your body fast enough. Decreased body flow to organs like the kidneys can lead to failure. Hypothyroidism can affect  fertility and menstruation in women, and testosterone levels and sperm shape in men. Myxedema coma is when you are severely hypothyroid with decreased mental status, hypothermia, and other symptoms from slowed function all over your body.

Speaking of replacement thyroid hormones...

If your TSH is too high...

Your doctor may prescribe you a higher dose of levothyroxine to suppress (lower) your TSH further. Other causes of a too high TSH might be explored, such as any new nodules or Thyroglobulin levels. 

If your TSH is too low...

Your doctor may prescribe you a lower dose of TSH in order to raise it. Monitoring will have to be done to ensure your TSH doesn't then become too high. Other levels like Free T4 or Free T3 may be looked at. There could be other reasons besides just too much replacement thyroid hormone medication.

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