Thyroid Reference Guide
Levothyroxine is a man-made hormone

Levothyroxine: Applications and Adverse Reactions

The artificial thyroid hormone variant levothyroxine is among the most frequently prescribed medications in the U.S. Here’s what you should know.

Levothyroxine is a hormone utilized to treat hypothyroidism or an underactive thyroid gland.

Hypothyroidism is the most prevalent thyroid disorder, especially among women, and can cause symptoms such as reduced energy and metabolism, depression, agitation, and more.

When the body is unable to generate sufficient natural thyroxine (T4) due to health issues like Hashimoto’s thyroiditis or surgical procedures, levothyroxine serves as a hormone replacement. This supplemental hormone therapy may also be prescribed if you are undergoing surgery or radiation therapy for thyroid cancer.

Levothyroxine Functioning

Thyroxine is among the hormones generated by the thyroid gland. It operates by binding to cells that regulate energy levels, heartbeat, digestive processes, as well as muscle and brain development. By attaching to the cell, thyroxine directly influences its functionality.

Levothyroxine functions similarly to thyroxine, serving as a substitute when the thyroid fails to produce adequate amounts of thyroxine.

When should you think about using levothyroxine?

The symptoms of hypothyroidism can resemble other conditions. However, anyone experiencing multiple new symptoms such as low energy, fatigue, cold sensitivity, forgetfulness, dry skin, or depression should consider undergoing a blood test to determine thyroid-stimulating hormone (TSH) and thyroid hormone (T4) levels.

While hypothyroidism can be managed with levothyroxine, it cannot be cured. Most patients will need to continue hormone replacement therapy for the remainder of their lives. Exceptions may include individuals with viral thyroiditis or those experiencing thyroid issues during pregnancy.

Medication Forms and Potencies

Levothyroxine is administered orally as directed by your healthcare professional, typically in tablet form. Tablets come in various strengths, ranging from 25 micrograms (mcg) to 300 mcg, with each potency distinguished by a specific color.

It is also available as a softgel capsule (Tirosint) or an oral solution (Tirosint-Sol) in strengths from 13 micrograms per milliliter (mcg/ml) to 200 mcg/ml.

For the tablet, if swallowing it is not preferred, you can crush it, combine it with water, and drink it immediately. The solution can be consumed either undiluted or mixed solely with water. The capsule, however, should not be cut or crushed and must be swallowed whole.

If oral medication is not possible, your healthcare provider may suggest using the capsule as a suppository. Both the softgel capsule and the oral solution are suitable alternatives for individuals with gastrointestinal issues.

In emergency situations, levothyroxine can also be administered via injection.

Levothyroxine Adverse Reactions

Like any medication, levothyroxine carries the risk of side effects. However, side effects are generally associated with doses that are either too high or too low. When the dosage is accurate, side effects are unlikely, as the drug replaces a hormone your body would naturally produce.

Common side effects include:

  • Reduced bone density
  • Fatigue
  • Weight loss (usually minor and at the beginning of treatment, as correcting hormone levels helps eliminate excess fluids)
  • Hair loss (temporary and usually occurs within the first few months of treatment, resolving on its own)
  • Insomnia (taking levothyroxine in the morning may help prevent this)
  • Joint pain
  • Skin rash
  • Vomiting or diarrhea
  • Headache
  • Fever
  • Leg cramps
  • Appetite changes
  • Heat sensitivity

Less frequent side effects include:

  • Menstrual changes
  • Breathing difficulties
  • Hives
  • Mood fluctuations
  • Chest pain or discomfort
  • Swelling of hands or feet
  • Stomach pain

Inform your healthcare provider if you experience any side effects, particularly if they are persistent or severe. Levothyroxine side effects are often related to taking a higher dosage than needed, so reducing the dose may help alleviate side effects.

Seek emergency medical attention if you have trouble breathing or experience swelling of your face, lips, throat, or tongue, which could indicate an allergic reaction.

Levothyroxine is well-tolerated by most adults and children and can be taken alongside most other medications. However, some individuals should not take the product, including those with adrenal conditions, high blood pressure, hyperthyroidism, heart disease, or those who are allergic to the drug.

Severe Levothyroxine Side Effects

There are some rare yet severe side effects that may result from levothyroxine toxicity (overdose):

  • Atrial fibrillation (a dangerous irregularity in heartbeat)
  • Rapid or weak pulse
  • Confusion
  • Sudden headache
  • Lack of coordination
  • Loss of consciousness
  • Heart attack
  • Heart failure

Interactions with Other Medications

Levothyroxine may interact with various medications. It’s crucial to inform your healthcare provider and pharmacist about any medications you are currently taking. They can help you minimize interactions by suggesting alternative medications or guiding you on the timing of your daily medications.

Drug interactions that negatively impact the absorption or enhance the elimination of levothyroxine in the body can increase the risk of the mentioned side effects. This is because, in such situations, the body isn’t being adequately treated for hypothyroidism. Inadequately treated hypothyroidism can heighten the risk of cardiovascular disease. Additionally, the side effects mentioned earlier might persist without resolution.

Medications and dietary supplements that decrease levothyroxine absorption in the body include:

  • Antacids
  • Ferrous sulfate (iron)
  • Calcium carbonate
  • Sevelamer hydrochloride
  • Lanthanum
  • Cholestyramine
  • Colesevelam

To minimize these interactions, take levothyroxine four hours before or after these medications.

Medications that interact with levothyroxine by increasing its removal from the body include:

  • Carbamazepine
  • Phenobarbital
  • Phenytoin
  • Rifampin

Your healthcare provider may suggest monitoring your thyroid lab results for four to eight weeks after starting or stopping these medications and adjusting your levothyroxine dose as needed.

For some drugs, it may be necessary to adjust the quantity of levothyroxine you consume to counteract the impact of their interactions. This encompasses medicines containing both estrogens and androgens, like contraceptive tablets or patches. In rare instances, specific cancer treatments, such as imatinib or sunitinib, might necessitate a boost in your levothyroxine intake.

Always inform your medical professional and pharmacist when beginning a new drug. They can collaborate to ensure that your levothyroxine dosage remains suitable and effective for you.

Interactions Between Food and Levothyroxine

There are particular foods that can influence the absorption and the levels of levothyroxine in your system. Coffee has a diminishing effect on levothyroxine absorption. To minimize the likelihood of interaction, it is advised to wait 30 minutes to an hour after taking your levothyroxine dose before having your first coffee.

Consult your healthcare practitioner about the possibility of using the softgel capsule or liquid form, as these types do not have interactions with coffee.

Additional food items that can impact levothyroxine absorption consist of soybeans, walnuts, and dietary fiber.

Guidelines for Administering Levothyroxine

To ensure levothyroxine is effective for you, adhering to your physician’s instructions is crucial. Take special note of the suggested time for consumption and whether it should be taken in conjunction with other medicines or separately. Typically, doctors advise taking levothyroxine in the early morning on an empty stomach, a minimum of 30 minutes before eating or consuming caffeinated drinks.

The medication begins to work right away, but it may require several weeks before you notice an alleviation in symptoms. Once you commence taking levothyroxine, you’ll need to undergo lab tests to monitor your thyroid levels.

The frequency of these tests will vary among individuals:

Adults ought to undergo lab tests approximately 6 to 8 weeks after initiating levothyroxine treatment. Based on the results, the doctor can decide if dosage adjustments are necessary. Subsequently, thyroid levels can be monitored every 6 months. Once an effective dose is established, adults only need annual checks or when there are changes in other medications.

For children, thyroid lab tests should be conducted 2 to 4 weeks after commencing levothyroxine. If their dosage is altered, another test should be done 2 weeks post-adjustment. Once stabilized, children’s levels should be examined every 3 to 4 months until growth is complete.

Pregnant women using levothyroxine should have their thyroid levels assessed every 4 to 6 weeks, particularly during the first and second trimesters. Due to increased metabolism, their dosage might need to be increased by roughly 30% during pregnancy.

Other factors that could necessitate levothyroxine dosage adjustments include:

Aging: Older people might be more susceptible to cardiac side effects when starting levothyroxine. They may also need a lower initial dose and a more gradual increase.

Weight fluctuations: Notify your doctor of any changes in your weight, so they can help you modify your dosage accordingly.

Hormonal shifts: Women approaching menopause may require higher levothyroxine doses compared to post-menopausal women.

Formulation changes: If you switch to a different levothyroxine formulation, inform your healthcare provider if your symptoms reappear or if you encounter any side effects. This may indicate that your dose needs adjustment.

Key Considerations

Storage: Proper storage of levothyroxine is essential to maintain its effectiveness. Always store the medication at room temperature, ranging from 68°F–77°F (20°C–25°C). Place it in a dry area, shielded from light. Generally, avoid storing medicines in the bathroom or above the stove.

For softgel capsules, retain them in their blister pack until consumption.

For levothyroxine oral solution, store it in the original foil pouch. After opening the pouch, keep individual ampules inside until ready for use. Ensure the pouch contents are utilized within three months of opening.

If you have queries regarding storage, consult the instructions on the medication packaging or speak with your pharmacist.

Travel: If travel plans are on the horizon, discuss with your healthcare provider at least a month prior to departure to obtain extra prescriptions or refills for your levothyroxine. This preparation will be helpful in case your medication is lost or depleted during the trip.

Your doctor may also suggest having your lab tests done before traveling to confirm your condition is stable. If you are venturing to a different time zone, inquire about the optimal time to take levothyroxine.

To prevent exposing your medication to extreme conditions, do not leave it in a car and always keep it in your carry-on luggage when flying.

Levothyroxine Alternatives

While levothyroxine is the preferred treatment for hypothyroidism, it may not be effective for everyone. There are other medications or supplements that could potentially help manage your symptoms, although not all alternatives are FDA-approved. Always consult your healthcare provider or pharmacist before considering an alternative to levothyroxine.

Liothyronine (Cytomel)

Liothyronine is a synthetic form of T3, the other hormone generated by the thyroid gland. It is approved for treating hypothyroidism, either alone or in combination with levothyroxine, and is considered a second-line treatment option.

Liothyronine can be taken orally as a tablet, once a day. It is available in strengths ranging from 5 to 75 mcg. Typically, the starting dose is 5 or 10 mcg daily.

For those over 65, with a cardiac condition, or transitioning from levothyroxine to liothyronine, healthcare providers may recommend starting at 5 mcg daily and gradually increasing the dose every one to two weeks. Most individuals require a maintenance dose of 25 mcg to 75 mcg daily.

Liothyronine’s side effects are similar to those of levothyroxine.

Armour Thyroid

Armour Thyroid is a natural thyroid hormone preparation containing both T4 and T3, derived from the dried thyroid glands of pigs. It is utilized to replace thyroid hormones in individuals with hypothyroidism.

Armour Thyroid is taken orally. The typical starting dosage is 30 mg, but individuals with certain heart conditions may require a lower dose. Your physician may incrementally increase your dose by 15 mg every two to three weeks until an effective dosage is achieved. Most people need between 60 mg and 120 mg per day.

Since Armour Thyroid has not been as thoroughly researched as levothyroxine and lacks FDA approval, it is not generally recommended by most experts as a treatment for hypothyroidism.

Frequently Asked Questions

What should I avoid while taking levothyroxine?

Levothyroxine is generally well-tolerated and was the third-most prescribed drug in the U.S. in 2020. Some supplements or foods containing fiber, calcium, or iron, when taken alongside tablet-form levothyroxine, can reduce its effectiveness, according to a review of 63 studies published in the journal Pharmaceuticals in 2021. Coffee and other caffeinated beverages may also hinder levothyroxine absorption, which is why doctors advise taking it at least 30 to 60 minutes before eating breakfast. If levothyroxine causes gastrointestinal issues when taken on an empty stomach, a gel capsule or liquid formulation with meals may be better tolerated.

Hormone therapies such as birth control pills, estrogen, or testosterone may necessitate adjustments in levothyroxine dosage.

What are rare side effects?

Rare yet serious side effects can arise from excessive levothyroxine intake. It is crucial to collaborate with your doctor to determine the appropriate dosage. Symptoms of overdose warrant immediate medical attention and may include chest pain, excessive sweating, confusion, anxiety, irregular heartbeat, uncontrollable shaking, or seizures.

Side effects can also resemble hyperthyroidism symptoms, or overactive thyroid. The most common of these include increased appetite, fatigue, and nervousness.

If an individual experiences side effects from levothyroxine, their blood hormone levels should be reevaluated.

What does levothyroxine do in your body?

Levothyroxine is a synthetic version of the hormone T4, which is generated by the thyroid gland and circulated through the bloodstream to aid in the functioning of every organ in the body.

Insufficient natural or synthetic thyroid hormones can cause the body’s essential systems, such as respiration, heart rate, and digestion, to slow down.

Levothyroxine serves as a substitute for T4 in an underactive thyroid, mimicking the hormone’s actions.

Administering levothyroxine in tablet, gel, or liquid form can alleviate symptoms by normalizing your T4 and TSH (thyroid-stimulating hormone) levels. Why was a type of levothyroxine taken off the market?

In 2018, Westminster Pharmaceuticals voluntarily recalled all dosages of its levothyroxine tablets as a precautionary measure due to potential contamination. The drugs were produced using ingredients from a Chinese pharmaceutical company that failed a U.S. Food and Drug Administration inspection. All of the recalled tablets had expiration dates ranging from 2019 to 2020. There were no reported adverse effects associated with the recall, which has since been lifted.

Update June 2023

More hypothyroidism patients are now getting treatments apart from levothyroxine, a commonly used hormone medicine. This trend was revealed in a study that will be shared at the ENDO 2023 meeting of the Endocrine Society in Chicago. Notably, the health impacts of these alternate treatments are not as well-known as levothyroxine, according to Matthew Ettleson, M.D., from the University of Chicago.

The thyroid produces hormones T3 and T4, and hypothyroidism results from insufficient hormone production. The main treatment is hormone replacement, typically synthetic T4, also known as levothyroxine. As hypothyroidism is widespread, levothyroxine is often prescribed. Treatment guidelines for hypothyroidism have changed recently, and some now propose adding synthetic T3 if T4 alone isn’t effective.

The latest study found that the number of patients treated with desiccated thyroid extract (DTE), a natural hormone containing T4 and T3, has risen from 5% to 10% over the past decade. Moreover, a patient’s location and the availability of physicians can influence whether they’re treated with T4, T3, or DTE.

Using a large U.S. claims database, the researchers analyzed thyroid hormone prescription data from 2010 to 2020. They examined patients receiving T4 alone; T3 therapy with or without T4; DTE with or without T4; and other treatments. Additionally, they evaluated the physician density and whether patients lived in urban or rural areas.

Over the 11-year period, 524,818 adult patients accounted for 537,594 new thyroid hormone prescriptions. Of the total, 89.0% got T4 alone, 8.8% received DTE therapy, and 2.0% got T3 therapy. The percentage of patients receiving DTE rose from 5.4% to 10.2% during the study period.

Prescriptions for DTE and T3 were not evenly distributed across the U.S., with higher rates in the West and Southwest. Patients in states with more endocrinologists were less likely to receive T3 or DTE therapy. Conversely, patients living in major metropolitan areas were more likely to receive T3 or DTE therapy.

Ettleson pointed out that disparities in access to endocrine care may cause these differences. He stressed the importance for doctors and researchers to monitor how these treatment choices impact patient health and quality of life.


MedlinePlus – MedlinePlus is a service provided by the U.S. National Library of Medicine and the National Institutes of Health (NIH). It offers reliable, up-to-date health information, including details on levothyroxine and its uses, side effects, and precautions.

British Thyroid Foundation – Thyroid Hormone Replacement: The British Thyroid Foundation is a UK-based charity dedicated to supporting people with thyroid disorders. Their website provides information on thyroid hormone replacement therapy, including the use of levothyroxine.

These sources should provide you with a solid foundation of information, but we recommend conducting your own research to find additional sources.

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