Levothyroxine is a generic drug that’s prescribed for various conditions, including hypothyroidism in adults and some children. Levothyroxine comes in several forms. The dosage can vary depending on what condition the drug is used to treat.
Levothyroxine oral tablet and oral capsule are approved by the Food and Drug Administration (FDA) to address:
- treating hypothyroidism (low levels of thyroid hormone) in adults and certain children
- reducing thyroid-stimulating hormone (TSH) levels to help manage a certain type of thyroid cancer in adults and certain children
Levothyroxine intravenous (IV) injection is approved by the FDA to treat myxedema coma (a severe form of hypothyroidism) in adults.
Levothyroxine is a hormone drug. The oral tablet form is available as the brand-name versions Synthroid and Unithroid. The oral capsule is available as the brand-name Tirosint. The IV injection form is only available as a generic drug.
Keep reading for specific information about the dosage of levothyroxine, including its strengths and how to take the medication. For a comprehensive look at levothyroxine, see this article.
Note: This article describes typical dosages for levothyroxine provided by the drug’s manufacturer. When taking levothyroxine, always follow the dosage prescribed by your doctor.
Boxed warning: Not to be used for the treatment of obesity or for weight loss
Levothyroxine has a boxed warning about its use as a treatment for obesity or weight loss. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). It alerts doctors and patients about drug effects that may be dangerous.
Thyroid hormones, including levothyroxine, should not be used for weight loss or to treat obesity. Levothyroxine isn’t effective for weight loss in people with a healthy thyroid gland. And taking doses that are higher than recommended can cause serious and life threatening side effects. These may include chest pain, fast or irregular heartbeat or pulse, and shortness of breath.
For more information about this warning, talk with your doctor or pharmacist.
Show MoreRead below for details about levothyroxine’s dosages for its approved uses.
Levothyroxine forms
Levothyroxine comes in three forms:
- oral tablet
- oral capsule
- powder in a single-dose vial that’s mixed with a liquid to form a solution for IV injection
Levothyroxine strengths
The different forms of levothyroxine come in the following strengths:
| Form | Strength |
|---|---|
| oral tablet | • 25 micrograms (mg) • 50 mcg • 75 mcg • 88 mcg • 100 mcg • 112 mcg • 125 mcg • 137 mcg • 150 mcg • 175 mcg • 200 mcg • 300 mcg |
| oral capsule | • 13 mcg • 25 mcg • 37.5 mcg • 44 mcg • 50 mcg • 62.5 mcg • 75 mcg • 88 mcg • 100 mcg • 112 mcg • 125 mcg • 137 mcg • 150 mcg • 175 mcg • 200 mcg |
| IV injection | • 100 mcg • 200 mcg • 500 mcg |
Typical dosages
Your dosage of levothyroxine will depend on several factors, including:
- your age
- body weight
- heart health
- other medical conditions you may have
- other medications you may take
- your diet
Typically, your doctor will start by prescribing you a low dosage. Then they’ll adjust it over time to reach the amount that’s right for you. Your doctor will ultimately prescribe the smallest dosage that provides the desired effect.
The following information describes dosages that are commonly prescribed or recommended in adults. However, be sure to take the dosage your doctor prescribes for you. Your doctor will determine the best dosage to fit your needs.
Dosage for hypothyroidism
Doctors may prescribe levothyroxine oral tablet or oral capsule to treat hypothyroidism.
The typical starting dose is 1.6 mcg per kilogram (kg) of body weight per day (mcg/kg/day). (One kg is about 2.2 pounds [lb].) However, if you have certain heart conditions or you’re age 65 years or older, your starting dose may be lower.
Your doctor will order blood tests to monitor your thyroid hormone levels during treatment. They’ll likely make dosage adjustments in amounts of 12.5 to 25 mcg every 4 to 6 weeks until your thyroid hormone levels are within a normal range. If you have certain heart conditions or are an older adult, your doctor may adjust your dosage every 6 to 8 weeks instead.
If you have severe, long-term hypothyroidism and are prescribed levothyroxine oral capsule, your doctor may recommend a starting dosage of 12.5 to 25 mcg per day. They’ll likely make dosage adjustments in amounts of 12.5 to 25 mcg every 2 to 4 weeks until your thyroid hormone levels are in the normal range.
For more information about your specific dosage, talk with your doctor.
Dosage for thyroid cancer
Levothyroxine oral tablet and oral capsule are also approved to reduce TSH levels to help manage a certain type of thyroid cancer. For this purpose, it’s typically taken with radioactive iodine treatment and surgery.
The recommended dosage of levothyroxine oral tablet will depend on the severity of your condition and what your target thyroid hormone levels are. Your doctor will recommend the right dosage based on your condition.
For levothyroxine oral capsule, the typical dosage is greater than 2 mcg/kg/day. But the specific dosage will depend on the severity of your condition.
For more details about your specific dosage, talk with your doctor.
Dosage for myxedema coma
Levothyroxine IV injection is used to treat myxedema coma. The recommended dosage varies depending on your age, physical condition, severity of your condition, and whether you have any heart-related conditions.
The typical dosage consists of a loading dose followed by a maintenance dose. (A loading dose is a higher dose of medication given at the beginning of treatment so the drug can start working more quickly. A maintenance dose is what you’ll take throughout treatment, often after a loading dose.)
The recommended loading dose is between 300 to 500 mcg. The recommended maintenance dosage is 50 to 100 mcg once per day.
Once your condition is stable and you can swallow pills, your doctor will switch you to an oral form of levothyroxine.
For more information about your specific dosage of levothyroxine injection, talk with your doctor.
Children’s dosage
Levothyroxine oral tablet is approved to treat hypothyroidism and a certain kind of thyroid cancer in children of all ages. Levothyroxine oral capsule is only approved for these uses in children ages 6 years and older.
Dosage for hypothyroidism in children
The dosage is based on your child’s body weight in kg. The dosage per kg is measured in mcg/kg and is calculated by your child’s doctor.
Below is a dosage chart by weight for using levothyroxine oral tablet to treat hypothyroidism in children:
| Child’s age | Daily starting dosage of levothyroxine oral tablet |
|---|---|
| 0 to 3 months | 10 to 15 mcg/kg |
| 3 to 6 months | 8 to 10 mcg/kg |
| 6 to 12 months | 6 to 8 mcg/kg |
| 1 to 5 years | 5 to 6 mcg/kg |
| 6 to 12 years | 4 to 5 mcg/kg |
| 13 years or older but still growing or going through puberty | 2 to 3 mcg/kg |
| no longer growing and puberty is complete | 1.6 mcg/kg |
Your child’s doctor will likely adjust the dosage every 2 weeks until your child’s thyroid hormone levels are within a normal range. If your child has a risk of heart problems or hyperactivity, their starting dosage may be lower.
The following table outlines the recommended dosage of levothyroxine oral capsule to treat hypothyroidism in children:
| Child’s age | Daily starting dosage of levothyroxine oral capsule |
|---|---|
| 6 to 12 years | 4 to 5 mcg/kg |
| 13 years or older but still growing or going through puberty | 2 to 3 mcg/kg |
| no longer growing and puberty is complete | 1.6 mcg/kg |
As with levothyroxine tablets, your child’s doctor may prescribe a lower starting dosage if your child has a risk of hyperactivity.
Talk with your child’s doctor if you have questions about their dosage.
Dosage for thyroid cancer in children
Levothyroxine oral tablet and oral capsule are also used to reduce TSH levels to help treat a certain kind of thyroid cancer. The dosage in children is the same as in adults. See the “Dosage for thyroid cancer” section for details.
Below are some frequently asked questions about levothyroxine.
What is considered a high dose of levothyroxine?
There is no maximum dosage of levothyroxine because dosing depends on several factors. These include why the drug is being prescribed, your medical condition, weight, and age. Also, each person’s body works differently. So you may respond differently to a dosage of the drug compared with another person taking the same dosage.
If you have concerns about your levothyroxine dosage, talk with your doctor or pharmacist.
Is there a levothyroxine dosage calculator?
Yes. There is a dosage calculator available for doctors, pharmacists, and other healthcare professionals. This is helpful for doctors as levothyroxine can require careful monitoring and frequent dosage adjustments.
If you have questions about how your dosage of levothyroxine was calculated, talk with your doctor or pharmacist.
Levothyroxine oral tablet or oral capsule should be swallowed whole once per day. Your doctor will likely recommend taking levothyroxine on an empty stomach, 30 minutes to 1 hour before breakfast. You should take levothyroxine 4 hours before or 4 hours after medications that may interact with it.
If you or your child cannot swallow tablets, levothyroxine oral tablet can be crushed and mixed with a small amount of water. The entire mixture should be taken right away with a spoon or dropper. See the instructions in the levothyroxine oral tablet prescribing information for more details.
Levothyroxine oral capsule cannot be cut, crushed, or chewed. If you have trouble swallowing pills, see this article for tips on how to take this form of medication. You can also talk with your doctor or pharmacist.
It may be helpful to take levothyroxine oral tablet or oral capsule around the same time of day. This helps maintain a steady level of the drug in your body so levothyroxine can work effectively.
The IV injection of levothyroxine will be given by your doctor or another healthcare professional at a clinic, doctor’s office, or hospital. First, they’ll mix the powder form of levothyroxine with a liquid to make a solution. Then they’ll prepare the liquid solution for injection into your vein. You may receive a few doses of the IV injection, and then your doctor may switch you to an oral form of levothyroxine to continue treatment.
If you have questions about how to take the oral forms of levothyroxine, talk with your doctor or pharmacist. For questions about how you’ll receive the IV injection form, talk with your doctor.
Long-term treatment
Levothyroxine is meant to be taken as a long-term treatment. If you and your doctor determine that levothyroxine is safe and effective for you, you’ll likely take it long term.
Before you start taking levothyroxine, your doctor will discuss your treatment plan with you.
ACCESSIBLE DRUG LABELS AND CONTAINERSSome pharmacies offer labels with large print, braille, or a code you scan with a smartphone to convert text to speech. If your local pharmacy doesn’t have these options, your doctor or pharmacist might be able to recommend a pharmacy that does.
If you’re having trouble opening medication bottles, ask your pharmacist about putting levothyroxine oral tablet or oral capsule in an easy-open container. They also may recommend tools that can make it easier to open bottles.
It’s important that you do not take more levothyroxine oral tablet or oral capsule than your doctor prescribes. Taking more than the recommended amount may lead to harmful effects or overdose.
Effects of an overdose
Overdose effects of levothyroxine can include:
- symptoms of hyperthyroidism (overactive thyroid), such as nervousness, trouble breathing, and itchy skin
- confusion
- disorientation
- seizures
- coma
If you take more than the recommended amount of levothyroxine
Call your doctor right away if you believe you’ve taken too much levothyroxine. Another option is to call America’s Poison Centers at 800-222-1222 or use its online tool. If you have severe symptoms, immediately call 911 or your local emergency number, or go to the nearest emergency room.
Disclaimer: Medical News Today has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.
