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Levothroid: What is it and How Does it Work?

Levothroid: What is it and How Does it Work?

Hypothyroidism affects approximately one out of every 20 people, or about 4.6 percent of Americans aged 12 and older. Women are more likely than men to suffer from hypothyroidism, and people over the age of 60 are also more likely to be diagnosed with the condition. Balanced thyroid hormones are important in order to carry out a number of bodily functions, including metabolism and the growth and repair of cells. Synthetic hormone medications, such as  Levothroid, can help patients with hypothyroidism minimize or avoid the most unpleasant symptoms of their condition. Hypothyroidism is so common that Levothroid is one of the top three most commonly prescribed medications in the United States, with nearly 102 million prescriptions written for the generic version of Levothroid, levothyroxine sodium, in 2017.  

What is Levothroid?

Levothroid is a brand name prescription medication that both treats hypothyroidism and suppresses TSH hormone in patients with certain types of cancer. Levothroid is a synthetic hormone that mimics T4, a naturally produced hormone in the thyroid gland. The generic version of Levothroid is levothyroxine sodium. Levothroid can be used to balance hormone levels in patients who do not produce enough T4 to meet their body’s needs. 

What conditions are treated with Levothroid?

Levothroid is used for both the treatment of hypothyroidism and TSH suppression in patients with certain thyroid conditions. The two uses of the medication are discussed briefly below.

Hypothyroidism

When the body does not produce enough thyroid hormones to carry out the functions of the body, patients are diagnosed with hypothyroidism. Thyroid hormones are responsible for regulating a number of different functions in the body including growth and repair of the body’s cells, assisting with digestion, and regulating the metabolism. The three types of hypothyroidism include primary hypothyroidism, secondary hypothyroidism, and tertiary hypothyroidism. Although each of the different types of hypothyroidism have different causes, all of the different types of hypothyroidism are treated with Levothroid in the same way and they all have the same symptoms. Symptoms of hypothyroidism include:

  • Weight gain
  • Hoarseness
  • Elevated blood cholesterol level
  • Slowed heart rate
  • Impaired memory
  • Fatigue
  • Constipation
  • Pain, stiffness, or swelling in the joints
  • Dry skin
  • Puffy face
  • Muscle weakness
  • Thinning hair
  • Depression
  • Enlarged thyroid gland
  • Increased sensitivity to cold
  • Muscle aches, tenderness, and stiffness
  • Heavier than normal or irregular menstrual periods

TSH Suppression

Thyroid stimulating hormone, also known as TSH, plays two roles in the body: it tells the thyroid gland to produce more T3 and T4 hormones, and it directs the growth of cells in the thyroid gland. As a result, TSH can cause some cancerous tumors to grow faster than they would in the absence of the hormone. Patients with thyrotropin-dependent well-differentiated thyroid cancer, in particular, can help prevent their tumors from spreading by suppressing their levels of TSH.  Although many early forms of thyroid cancer have no noticeable symptoms, some patients may experience the following symptoms in later stages:

  • A lump in the throat
  • Pain in the throat and neck
  • A cough
  • Swollen lymph nodes in the neck
  • Hoarseness
  • Difficulty swallowing

How does Levothroid work?

Levothroid works slightly differently depending on which condition it is being used to treat. The human body naturally produces two primary thyroid hormones: T3 and T4. T4 can be used to create T3, so Levothroid works by replacing or supplementing the levels of T4 in the body. Although Levothroid is a synthetic hormone, the body recognizes it in the same way as T4. Patients with hypothyroidism use Levothroid to increase the amount of T4 in the body, which in turn directs the body to begin producing T3. As a result, the hormone levels become more balanced. Once the body has adequate, balanced levels of T3 and T4, many of the symptoms of hypothyroidism are minimized or eliminated. 

When the medication is used to treat thyrotropin-dependent well-differentiated thyroid cancer, Levothroid works by reducing TSH levels. TSH is a hormone in the body that directs the thyroid to make T3 and T4 and also stimulates the growth of cells in the thyroid gland. When the body has a sufficient amount of T3 and T4, it does not need to produce more TSH. Levothroid works by increasing the levels of T4, and by proxy, T3, in the body, thereby suppressing TSH. Patients who have certain types of thyroid cancer can experience faster growth rates of their tumors when TSH is being produced.  Lower levels of TSH mean that cells in the thyroid gland, including cancer cells, do not grow or reproduce as quickly. Patients with certain types of thyroid cancer can minimize the growth and spread of their disease by suppressing their TSH levels using Levothroid. 

What side effects are associated with Levothroid?

The majority of side effects associated with Levothroid are caused by taking too much of the medication. Although the list of side effects caused by Levothroid is long, most can be avoided if patients take exactly the amount of Levothroid that is prescribed by their doctor at the same time each day and are sure to follow the prescribing instructions carefully. Side effects of Levothroid that usually do not require medical attention include:

  • Weight gain or loss
  • Change in appetite
  • Diarrhea
  • Abdominal or stomach cramps
  • Crying
  • Feelings of suspicion and distrust
  • Headache
  • Trouble sitting still
  • Vomiting
  • Redness of the face, neck, arms, and occasionally upper chest
  • Trouble getting pregnant
  • Unusual tiredness or weakness
  • Feeling things are not real
  • Hair loss
  • Quick to react or overreact emotionally 
  • False or unusual sense of well being
  • Feeling unwell or unhappy
  • Feeling of warmth
  • Increased appetite
  • Muscle weakness
  • Mental depression
  • Fear or nervousness
  • Feeling of discomfort
  • Rapidly changing moods
  • Restlessness

Other side effects of Levothroid can be serious and require immediate medical attention. If you experience any of the following side effects, it’s important to seek medical attention immediately:

  • Dilated neck veins
  • Irritability
  • Menstrual changes
  • Difficulty with swallowing
  • Extreme fatigue
  • Seizures
  • Sweating
  • Tightness in the chest
  • Decreased urine output
  • Chest pain or discomfort
  • Difficult or labored breathing
  • Pain or discomfort in the arms, jaw, back or neck
  • Swelling of the eyes, face, lips, throat, or tongue
  • Nausea
  • Fainting
  • Fever
  • Hives or welts, skin itching, rash, or redness
  • Dizziness
  • Lack or slowing of normal growth in children
  • Blurred or double vision
  • Eye pain
  • Limp or walk favoring one leg
  • Fast, slow, irregular, pounding, or racing heartbeat or pulse
  • Heat intolerance
  • Irregular breathing
  • Tremors
  • Pain in the hip or knee
  • Severe headache

Patients who take too much Levothroid can overdose on the medication, causing a medical emergency. Patients should seek immediate medical attention if they experience any of the following symptoms:

  • Fast or weak pulse
  • Lightheadedness
  • Sudden slurring of speech
  • Loss of consciousness
  • Disorientation
  • Change in consciousness
  • Sudden loss of coordination
  • Cold, clammy skin
  • Confusion
  • Sudden headache

Most side effects caused by Levothroid occur when hormones in the body become imbalanced due to taking too high or too low of a dose of the medication. For this reason, it is important that patients do not change their dose of Levothroid or take it differently than prescribed without first discussing the changes with their doctor. Because even a small change in the dose of the medication can result in large changes in the body’s hormone levels, it’s important to use caution when taking Levothroid. Side effects experienced as a result of taking too much Levothroid tend to mirror the symptoms of hyperthyroidism, including weight loss, trouble sleeping, fast heart rate, feeling nervous or anxious, heart palpitations, and muscle weakness. Side effects experienced as a result of taking too little Levothroid tend to mirror the symptoms of hypothyroidism, including weight gain, muscle weakness, tiredness, constipation, and hair loss. Many side effects associated with Levothroid can be avoided by taking your medication at the same time each day and sticking to the dose prescribed by your doctor. 

Sources:

https://www.mayoclinic.org/diseases-conditions/hypothyroidism/symptoms-causes/syc-20350284 

https://www.healthline.com/health/thyroid-cancer#symptoms 

https://www.webmd.com/drugs/2/drug-1812/levothroid-oral/details 

https://www.drugs.com/dosage/levothroid.html 

https://dailymed.nlm.nih.gov/dailymed/drugInfo