Euthyrox dosage, forms, and strengths

Euthyrox is a brand-name prescription drug that treats underactive thyroid (hypothyroidism) and thyrotropin-dependent well-differentiated thyroid cancer. Its active ingredient, levothyroxine sodium, is a synthetic version of the thyroid hormone thyroxine, called T4 for short. T4 is essential to many of the body’s functions including metabolism, energy, growth, and development. In people with hypothyroidism, Euthyrox replaces the T4 hormone normally produced by the thyroid gland. For thyroid cancer, however, Euthyrox suppresses the production of thyroid stimulating hormone (TSH), a hormone that can provoke some forms of thyroid cancer to grow more aggressively. 

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Euthyrox forms and strengths

Euthyrox is taken orally. Although there is only one dosage form, Euthyrox comes in 12 different dosage strengths to allow for a wide range of individualized doses: 

• Tablet: 25 micrograms (mcg), 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg

Euthyrox dosage for adults

Healthcare professionals prescribe Euthyrox as hormone replacement therapy for people with an underactive thyroid (hypothyroidism). It’s also FDA-approved to treat certain types of thyroid cancer whose growth is stimulated by thyroid-stimulating hormone, also called thyrotropin.

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Euthyrox dosage for hypothyroidism

The most common reason people take levothyroxine is to bring low thyroid hormone levels back to normal. Thyroid hormones regulate life processes throughout the body including growth, energy, weight, internal temperature, skin, hair, nail growth, and many cellular functions. That means healthy thyroid levels are essential to good health. There are many reasons why a thyroid gland doesn’t produce enough thyroid hormone. Euthyrox does not fix any of those problems. It’s only a substitute for the hormones the thyroid should be producing. That means people with an underactive thyroid may need to take daily doses for years if not a lifetime. Healthcare professionals will take regular blood tests to ensure the effectiveness of therapy and make dose adjustments as needed. 

For most people, the doses will start at the full replacement dose of 1.6 mcg per kilogram of body weight. That’s a large enough dose to replace all the thyroid hormone a person with healthy thyroid function would produce. For a 150-pound person, that’s about 100 mcg. After a while, the healthcare provider will incrementally adjust the levothyroxine doses up or down until thyroid-stimulating hormone concentrations are within the normal range on laboratory tests. 

• Standard Euthyrox dosage for adults: 50-200 mcg taken once daily

• Maximum Euthyrox dosage for adults: 300 mcg daily

Euthyrox dosage for thyroid cancer

Some forms of thyroid cancer are affected by a hormone called thyrotropin or thyroid stimulating hormone, a hormone produced by the pituitary gland. This hormone stimulates the cancer cells to grow. These cancers are called thyrotropin-dependent thyroid cancer. Treatment consists of surgery and radioiodine therapy, but people will also take levothyroxine to suppress TSH. That’s because TSH is produced in response to thyroid hormone levels. If thyroid hormone levels go up, TSH levels go down, decreasing the growth rate of the cancer. Doses vary widely. Healthcare providers will use whatever dose is necessary for adequate TSH suppression. Even after the cancer is cured, people will need to continue taking levothyroxine because of loss of thyroid function.

Euthyrox dosage for children

Euthyrox is used in children for the same reasons it’s used in adults: as hormone replacement therapy for an underactive thyroid or as part of the treatment for thyrotropin-dependent thyroid cancer. The FDA has approved levothyroxine treatment in children as young as newborns. Pediatric doses for hypothyroidism have been standardized, but thyroid cancer treatment requires whatever dose is adequate for TSH suppression. If the child is too young to swallow a tablet, parents or caregivers can crush it in a small amount of water and give it that way.

Euthyrox dosage restrictions

Euthyrox has a number of possible dose adjustments for specific people or medical conditions. These include:

• Heart disease: Adults with cardiovascular disease will start at a lower dose than other adults: 12.5–50 mcg/day and will need to be monitored for the onset of cardiac symptoms. The dose will be adjusted by 12.5–25 mcg/day every six to eight weeks until an effective dose is reached.

• Seniors: People older than 60 years of age will also start at a lower dose: 12.5-25 mcg/day. The dose will be adjusted by 12.5-25 mcg/day every six to eight weeks until an effective dose is reached.

• Pregnancy: Pregnant women previously on levothyroxine will require their dose to be increased by 20-30% to meet the increased demands of pregnancy. The dose will be returned to pre-pregnancy levels immediately after delivery.

• Newborns at risk of heart failure: Healthcare providers will start at a lower dose.

• Children at risk for hyperactivity: Healthcare providers will start at a lower dose and increase the dose weekly for four weeks until the full dose is achieved. 

• Renal impairment: No dosage modifications are recommended.

• Hepatic impairment: No dosage modifications are recommended.

• Obesity: Initial doses should be based on lean body weight rather than actual body weight.

Levothyroxine is not safe to take by people with certain medical conditions. Contraindications include people with dangerously high levels of thyroid hormone (thyrotoxicosis) and people with untreated adrenal insufficiency.

Euthyrox dosage for pets

Levothyroxine is used as thyroid hormone replacement therapy in cats and dogs with underactive thyroid. Because doses between dogs and humans vary significantly, veterinarians prescribe a formulation developed specifically for dogs called Thyro-Tabs Canine. Levothyroxine is as safe for dogs and cats as it is for humans, but starting doses are not as well-standardized as they are for humans. As with humans, veterinarians will take regular blood tests and adjust the doses accordingly, so pet doses are as variable as they are for humans.

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How to take Euthyrox

Euthyrox is a tablet taken once per day by mouth in the morning preferably on an empty stomach. Once Euthyrox is started, it may take several weeks to notice any improvement in symptoms.

• Take your medicine as directed. Your dose may need to be changed several times to find what works best for you.

• Euthyrox tablets should be taken in the morning on an empty stomach 30-60 minutes before breakfast and other medications. If a morning dose is difficult, you may also take this medication at night at least three to four hours after your last meal, but doses should be taken consistently at the same time each day.

• Do not remove Euthyrox tablets from their blister pack until you’re ready to take the tablet.

• If you take calcium supplements, calcium carbonate, iron supplements, or antacids (particularly those containing magnesium or aluminum), take Euthyrox at least four hours before or after taking one of these supplements or antacids.

• If you are giving this medicine to a baby or child who cannot swallow the tablet whole:

  • Crush the tablet and mix it in 1 to 2 teaspoons (5 to 10 mL) of water, breast milk, or non-soy-based formula.

  • Immediately give the mixture to the child using a spoon or dropper. Do not store the mixture for future use.

• Don’t stop taking Euthyrox without asking your healthcare provider. 

• Store the medicine in a child-proof closed container at room temperature protected from moisture and light.

Euthyrox dosage FAQs

How long does it take Euthyrox to work?

Once a dose is taken, it takes two to four hours for levothyroxine levels to peak in the bloodstream. However, it may take four to six weeks after you’ve started Euthyrox to notice any improvement in symptoms.

How long does Euthyrox stay in your system?

With a half-life of 6 to 7 days, a dose of Euthyrox can take as long as five weeks to be cleared from the body.

What happens if I miss a dose of Euthyrox?

Euthyrox is taken once per day. If a dose is forgotten, take it on the same day it was scheduled. If it’s the next day, skip the missed dose and take your Euthyrox tablet when you normally take it. Do not take an extra dose to make up for a missed dose. 

How long can you take Euthyrox?

Euthyrox is a long-term, even lifelong treatment. There are no side effects associated with long-term use of levothyroxine.

How do I stop taking Euthyrox?

Do not stop taking Euthyrox except under the medical advice of a healthcare provider. In most people, levothyroxine is a lifelong treatment for hypothyroidism. If the treatment is stopped, symptoms of hypothyroidism will return. Before stopping this medicine, make sure an adequate substitute has been prescribed.

What is the maximum dosage for Euthyrox?

Maintenance doses of >300 micrograms per day are rarely used. Euthyrox dosages must be individualized for thyroid hormone replacement. There are no maximum dosage guidelines for TSH suppression in people with thyroid cancer.

Can you overdose on Euthyrox?

There are two ways to overdose on Euthyrox: you can take too much of your prescribed medication or you can use Euthyrox when there’s no medical reason to take it. You should never use levothyroxine or other thyroid hormones for weight loss or athletic performance. Symptoms of an overdose or misuse of levothyroxine are the same as they are for an overactive thyroid (hyperthyroidism): increased energy, restlessness, irritability, anxiety, mood swings, and trouble sleeping. A high enough overdose can cause severe problems such as chest pain, confusion, fast or irregular heartbeat, hallucinations, stroke, coma, or death.

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What interacts with Euthyrox?

Thyroid hormones are a natural and constant part of the human body’s function, so drug interactions with levothyroxine are minimal. The biggest issue involves drugs, supplements, and foods that interfere with the body’s ability to absorb levothyroxine tablets. Talk to a healthcare provider before taking levothyroxine with:

• Gas medications like simethicone

• Stomach acid reducers

• The ulcer medication sucralfate

• The cholesterol-lowering medications colestipol and cholestyramine

• The obesity drug orlistat

• Warfarin

As a general rule, don’t take these supplements or eat these foods within four hours of a levothyroxine dose: 

• Supplements such as:

  • Iron (particularly ferrous sulfate)

  • Calcium carbonate

  • Antacids

  • Magnesium

  • Multivitamins

• Foods such as:

  • Soy products or soybean flour

  • Grapefruit or grapefruit juice

  • High-fiber foods

Many other drugs may alter the effects of levothyroxine such as the heart rhythm drug amiodarone or estrogen treatment in postmenopausal women. This is not a complete list of interactions so make sure to tell your prescribing healthcare provider about all the prescription drugs, over-the-counter remedies, and supplements that you take. Before starting or stopping any new medications, always discuss these changes with your healthcare provider if you are on levothyroxine.

What happens when you mix Euthyrox and alcohol?

People taking Euthyrox can drink alcohol without altering the medication’s effects.

Is it safe to take Euthyrox during pregnancy?

Euthyrox is safe to take during pregnancy. Because of the increased demands of pregnancy, dose adjustments will be required, usually 20% to 30% higher than normal. Doses will return to normal after delivery.

Is it safe to take Euthyrox when breastfeeding?

Euthyrox is safe to take while breastfeeding. There is no evidence that it will affect lactation or harm the nursing infant.

Sources

• Euthyrox levothyroxine sodium tablet prescribing information, NIH National Library of Medicine

• Levothyroxine, StatPearls

• Levothyroxine sodium drug summary, Prescriber’s Digital Reference

• Treatment of thyroid cancer, by types and stages, American Cancer Society