Levothyroxine Mechanism of Action

Instructor: Justine Fritzel

Justine has been a Registered Nurse for 10 years and has a Bachelor's of Science in Nursing degree.

Many people take the prescription medication called levothyroxine. In this lesson, we will learn about what this medication is used for and how it works.


Amanda is a 41-year-old woman that has been dealing with depression over the last year. She has been fatigued and has gained weight which she attributes to her depression. She tried different approaches to overcome her depression with no relief and finally decides to see her physician. Her physician asks her several questions and orders blood work.

Thyroid Gland

The next week she goes in for a follow-up appointment with her physician. He tells her that she has hypothyroidism which is an underactive thyroid gland. He explains that her depression, weight gain, and fatigue are likely due to this. He also points outs that her thinning hair, dry skin, constipation, and painful muscles and joints are also symptoms of hypothyroidism. He writes her an order for a medication to treat this.

Medication Used to Treat Hypothyroidism

Levothyroxine is the generic name for a prescription medication used to treat hypothyroidism. Brand names include Synthroid, Levoxyl, and Levothroid. This drug is classified as a thyroid medication for hypothyroidism.

Levothyroxine is a synthetic version of the thyroid hormone produced in your body. Let's look closer at how levothyroxine works next!

How Levothyroxine Works

Your thyroid produces thyroxine (T4) and triiodothyronine (T3) which are both hormones. T3 is the more active hormone and T4 is converted into T3 in the body. These hormones increase the metabolic rate of all tissues in the body. It helps to maintain brain function, metabolism, body temperature, as well as many other bodily functions.

Levothyroxine is the man-made version of thyroxine. When your thyroid is underactive and not producing enough thyroxine, it slows down your metabolism. This results in the symptoms of weight gain and fatigue.

When you take levothyroxine, it acts in the same way thyroxine does and brings the bodies T3 and T4 levels back up to normal. It replaces the thyroxine levels that you are lacking due to your underactive hypothyroid and returns your metabolism where it should be as well as maintaining the many other bodily functions.

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