How Long Does It Take for Levothyroxine to Start Working?

how long does it take for levothyroxine to start working

How long does it take for Levothyroxine to Start Working:

The thyroid gland is a crucial endocrine gland that produces and releases two main hormones – thyroxine (T4) and triiodothyronine (T3). These hormones help regulate the body’s metabolism, heart rate, blood pressure, weight, and body temperature.

Abnormalities in the thyroid gland can lead to a variety of health problems. Hypothyroidism or an underactive thyroid develops in the body when the gland fails to produce sufficient T3 and T4, leading to various symptoms such as fatigue, dry skin, depressed mood, weight gain, and cold intolerance.

Treatment for hypothyroidism typically involves taking daily hormone replacement medication, such as levothyroxine. It’s a synthetic form of the thyroid hormone thyroxine, developed and released by the thyroid gland. Treatment with levothyroxine is typically lifelong and must be taken regularly to maintain proper thyroid hormone levels in the body.

In this article, we will talk about hypothyroidism and address some common questions, such as how long does it take for levothyroxine to start working:

Causes of Hypothyroidism

Common causes of hypothyroidism include:

  • Autoimmune disorders – The most common cause of hypothyroidism is the autoimmune disorder called Hashimoto’s thyroiditis, in which the immune system damages the thyroid gland.
  • Surgery – Removing the thyroid gland, either partially or completely, can lead to hypothyroidism. It’s often done to treat thyroid cancer or other thyroid disorders.
  • Radiation treatment – Treatment for certain cancers, such as head and neck cancer, can damage the thyroid gland and lead to hypothyroidism.
  • Medications – Some medications, such as lithium and amiodarone, can interfere with the production of thyroid hormones and lead to this condition.

Effects and Treatment of Hypothyroidism

When the thyroid gland doesn’t make enough hormones, it can affect other organs and systems in the body, including:

  • The cardiovascular system – Hypothyroidism can increase the risk of high cholesterol and heart disease.
  • The digestive system – Hypothyroidism can cause constipation alongside bloating.
  • The nervous system – Hypothyroidism can cause fatigue, depression, and memory problems.
  • The skin – Hypothyroidism can cause dry, flaky skin and hair loss.
  • The reproductive system – Hypothyroidism can cause menstrual irregularities and fertility problems in women.

Levothyroxine is a form of the thyroid hormone thyroxine used as a treatment for hypothyroidism. Levothyroxine is available as a prescription medication and is taken orally to replace the missing thyroid hormones in the body. Levothyroxine is usually taken once daily with a glass of water (on an empty stomach). It’s crucial to take levothyroxine at the same time every day, as directed by the healthcare provider.

If you’re wondering: how long does it take for levothyroxine to start working, read below.

How Long Does It Take for Levothyroxine to Start Working?

After levothyroxine is taken, it is absorbed into the bloodstream and transported to the body’s cells, where it is needed. Once inside the cells, levothyroxine is converted into the active thyroid hormone triiodothyronine (T3). T3 is responsible for regulating the body’s metabolism and properly functioning the brain, heart, and nervous system.

Knowing exactly how long it takes for levothyroxine to start working is difficult. It usually takes several weeks for levothyroxine to start working and for symptoms of hypothyroidism to improve. Some people may notice an improvement in their symptoms within the first week of starting treatment, while others may not notice any improvement until several weeks or months later.

A viable way to determine how long it takes for levothyroxine to start working is to have regular check-ups with your healthcare provider to monitor your thyroid hormone levels.

Dosage of Levothyroxine

Generally, the starting dose of levothyroxine for adults with hypothyroidism is 50 to 100 micrograms per day. Children and adolescents with this condition may be started on a lower dose of levothyroxine, typically around 25 to 50 micrograms per day. The dosage may be increased or decreased based on the individual’s response to the medication and their thyroid hormone levels, as measured by a blood test.

If you forget to take levothyroxine

If you forget to take levothyroxine, your body may not have enough thyroid hormone, leading to symptoms such as fatigue, dry skin, and constipation. And if levothyroxine is not taken for an extended period, it can also lead to a heightened blood cholesterol level and risk of heart disease.

So, if you have missed your dose, take your next dose at the regular time. Remember not to take two doses simultaneously to make up for a missed dose.

If you take too much levothyroxine

Taking too much of this med can cause symptoms of hyperthyroidism, a severe condition in which the thyroid gland produces too much thyroid hormone. Symptoms of hyperthyroidism can include weight loss, rapid heartbeat, nervousness, irritability, and sweating. In severe cases, taking too much can lead to thyrotoxicosis, which can cause life-threatening complications such as heart failure and coma.

It is recommended to contact your healthcare provider immediately if you think you may have taken too much levothyroxine.

Who Cannot Take levothyroxine?

Levothyroxine is generally well-tolerated and safe for most people to take. However, some individuals may need to practice caution when taking the medication.

  • It’s contraindicated for people with a hypersensitivity or allergic reaction to levothyroxine or its ingredients.
  • People with uncorrected adrenal insufficiency are also not recommended to use it, as the medication may worsen this condition.
  • People with cardiovascular disease, angina or arrhythmias, and diabetes need to work closely with their healthcare providers to determine the best treatment using levothyroxine.
  • Levothyroxine is also not recommended for use in pregnancy or women who are breastfeeding, as the medication may be harmful to a developing fetus or nursing infant.

While determining how long does it take for levothyroxine to start working, let us also investigate its interactions with other medicines.

Cautions With Other Medicines

Several medications may interact with levothyroxine and impact its effectiveness. These include:

  • Iron supplements or antacids containing aluminum or calcium, which may affect the absorption of levothyroxine
  • Cholestyramine, a medication used to lower cholesterol levels, may also interfere with the absorption of levothyroxine
  • Warfarin, a blood thinner, may increase the risk of bleeding if taken with levothyroxine
  • Estrogen-containing medications, such as birth control pills, may reduce the effectiveness of levothyroxine
  • Lithium – used to treat bipolar disorder – may increase the risk of side effects if taken with levothyroxine
  • Amiodarone – used to treat irregular heartbeat – may increase the risk of thyroid problems if taken with levothyroxine

So, talk to your healthcare provider about potential drug interactions with levothyroxine and follow their instructions for taking your medication.


Levothyroxine is an effective medicine for treating hypothyroidism. If you’re wondering how long does it take for levothyroxine to start working? In general, levothyroxine aims to restore normal thyroid hormone levels and improve hypothyroidism symptoms or goiter. You may notice an improvement in your symptoms within the initial few days of starting treatment. However, it may take several weeks or even months for the medication to reach its full effect.


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