Levothyroxine is a generic prescription drug used to treat hypothyroidism and thyroid cancer in certain situations. The drug comes as an oral tablet. You usually take it once daily.
Levothyroxine is used in adults and certain children to treat hypothyroidism. It’s also used in adults to treat thyroid cancer in certain situations.
Levothyroxine belongs to a group of drugs called thyroid hormones.
This article describes the dosages of levothyroxine, as well as its strengths and how to take it. For a detailed overview of this drug, check out this in-depth levothyroxine article.
The table below highlights the basics of levothyroxine’s dosage for adults. Doses are listed in micrograms (mcg), and some are in mcg per kilogram (mcg/kg) of body weight. For reference, 1 kg is about 2.2 pounds (lb).
| Who it’s prescribed for | Typical starting dosage |
|---|---|
| • adult with a recent diagnosis of hypothyroidism who is otherwise healthy | 1.6 mcg/kg of body weight daily |
| • adult who has had hypothyroidism for a long time • adult who has hypothyroidism and a heart condition • older adult (age 65 years or older) who has hypothyroidism and a heart condition | 12.5 to 25 mcg daily |
Keep reading for more details about levothyroxine’s dosage
What is levothyroxine’s form?
Levothyroxine is available as an oral tablet.
What strengths does levothyroxine come in?
Levothyroxine comes in 12 strengths:
- 25 micrograms (mcg)
- 50 mcg
- 75 mcg
- 88 mcg
- 100 mcg
- 112 mcg
- 125 mcg
- 137 mcg
- 150 mcg
- 175 mcg
- 200 mcg
- 300 mcg
What are the usual dosages of levothyroxine in adults?
Your dosage will depend on your specific situation. Your doctor may start you on a low dosage and adjust it over time to reach the right amount for you. They’ll ultimately prescribe the smallest dosage that provides the desired effect.
The information below describes dosages that are commonly used or recommended. In some cases, doctors may adjust your dosage from those shown below. But be sure to take the dosage your doctor prescribes for you. They’ll determine the best dosage to fit your needs.
Dosage for hypothyroidism
The levothyroxine dosage for adults with hypothyroidism may depend on the following factors:
- your age
- your weight
- other medications you take
- foods you eat
- other medical conditions you have, especially heart problems
- your thyroid hormone levels
If you’ve received the diagnosis of hypothyroidism recently, your doctor will prescribe a starting dosage. It’s usually 1.6 mcg/kg of body weight to be taken once daily. This is also known as the average dose. For example, if you weigh 70 kg (about 154 lb), your likely starting dosage will be 100 to 125 mcg to be taken once daily. (In comparison, a dosage of 25 mcg, 50 mcg, or 100 mcg once daily would not be considered a high dose.)
Your doctor will check your thyroid levels every 4 to 6 weeks. If needed, they’ll adjust your dose in increments of 12.5 to 25 mcg.
For some people, doctors will prescribe a lower starting dosage. This is usually 12.5 to 25 mcg to be taken once daily. These include people who:
- have had hypothyroidism for a while
- have hypothyroidism and a heart condition
- are older adults (ages 65 years and older) with hypothyroidism and a heart condition
If you’ve had hypothyroidism for a while, your doctor may adjust your dose every 2 to 4 weeks. If you’re an older adult or have a heart condition, your doctor may adjust your dose every 6 to 8 weeks.
Dosage for thyroid cancer
For adults with thyroid cancer, in certain situations, the dosage of levothyroxine depends on body weight. You may be prescribed a dosage of at least 2 mcg/kg of body weight to be taken once daily. For example, someone who weighs 70 kg may be prescribed a dose of 137 to 150 mcg to be taken once daily.
For thyroid cancer, levothyroxine is usually prescribed in combination with surgery and radioactive iodine therapy.
What’s the dosage of levothyroxine for children?
Levothyroxine is used to help treat hypothyroidism in children as young as newborns (ages 0 to 3 months).
The dosage for children may be based on their age, weight, and growth stage. This levothyroxine dosage chart shows recommended children’s starting dosages:
| Age | Recommended starting dosage |
|---|---|
| 0 to 3 months | 10 to 15 mcg/kg of body weight daily |
| 3 to 6 months | 8 to 10 mcg/kg of body weight daily |
| 6 to 12 months | 6 to 8 mcg/kg of body weight daily |
| 1 to 5 years | 5 to 6 mcg/kg of body weight daily |
| 6 to 12 years | 4 to 5 mcg/kg of body weight daily |
| over 12 years and still growing | 2 to 3 mcg/kg of body weight daily |
| growth and puberty complete | 1.6 mcg/kg of body weight daily |
The above chart is recommended based on prescribing information. Your child’s doctor will prescribe the best dosage for your child.
If your child is a newborn at risk of heart problems, the doctor may prescribe a low starting dose. They may increase it every 4 to 6 weeks as needed.
If your child is at risk of hyperactivity, your doctor may choose a graduated starting dose. They’ll usually prescribe 25% of the recommended dose (shown in the children’s dosing chart above). Then they’ll gradually increase the dose weekly.
For more information about levothyroxine’s dosage for children, talk with your child’s doctor or a pharmacist.
Is levothyroxine used long term?
Yes, levothyroxine is usually a long-term treatment. You and your doctor can determine whether it’s safe and effective for your condition. If you agree that it is, you’ll likely take it long term.
It’s important to know that decreased bone mineral density is a risk associated with long-term levothyroxine treatment. This is especially relevant for women in postmenopause and older adults (ages 65 years and older).
Talk with your doctor to learn more about risks associated with long-term levothyroxine treatment.
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You should swallow your levothyroxine dose once daily with water. You’ll take each dose 30 minutes to 1 hour before your first meal of the day. Try to take your dose at the same time of day every day.
If you take certain drugs, you may need to space your dose of levothyroxine apart from them by 4 hours. And if you regularly eat certain foods within 1 hour of taking levothyroxine, your doctor may adjust your dose.
If your child cannot swallow tablets, you may crush their levothyroxine dose. Mix the crushed tablet in 1 to 2 teaspoons of water. Then give your child the dose right away using a dropper or spoon.
Do not take more levothyroxine than your doctor prescribes, as this can lead to harmful effects.
Symptoms of overdose
Symptoms caused by an overdose can include:
In rare cases, an overdose of levothyroxine may cause death.
What to do in case you take too much levothyroxine
Call your doctor right away if you think you’ve taken too much levothyroxine. You also can call 800-222-1222 to reach America’s Poison Centers or use its online resource. But if you have severe symptoms, immediately call 911 or your local emergency number. Or go to the nearest emergency room.
Disclaimer: Healthline 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.