Levothyroxine is a prescription drug. It comes as a tablet or capsule you take by mouth. It also comes as an injectable solution that’s only given by a healthcare provider.
Levothyroxine oral tablet is available as the brand-name drugs Levoxyl, Synthroid, and Unithroid. It’s also available as a generic drug. Generic drugs usually cost less than the brand-name version. In some cases, they may not be available in every strength or form as the brand-name drug.
Levothyroxine oral tablet may be used as part of a combination therapy. This means you may need to take it with other medications.
Why it’s used
Levothyroxine oral tablet is used to treat hypothyroidism. This is a condition when your thyroid gland produces too little thyroid hormone.
Levothyroxine also can be used to treat goiter, which is an enlarged thyroid gland. It also treats certain types of thyroid cancer.
How it works
Levothyroxine belongs to a class of drugs called hormones. A class of drugs is a group of medications that work in a similar way. These drugs are often used to treat similar conditions.
Levothyroxine works by providing the thyroid hormone that your thyroid gland would produce if it were working normally.
Levothyroxine oral tablet can cause side effects.
More common side effects
The more common side effects of levothyroxine can include:
- increased appetite
- weight loss
- heat sensitivity
- excessive sweating
- headache
- hyperactivity
- nervousness
- anxiety
- irritability
- mood swings
- trouble sleeping
- tiredness
- tremors
- muscle weakness
- changes in menstrual periods
- hair loss (usually temporary)
- diarrhea
- vomiting
- stomach cramps
If these effects are mild, they may go away within a few days or a couple of weeks. If they’re more severe or don’t go away, talk to your doctor or pharmacist.
Serious side effects
Call your doctor right away if you have serious side effects. Call 911 if your symptoms feel life threatening or if you think you’re having a medical emergency. Serious side effects and their symptoms can include the following:
- Heart attack. Symptoms can include:
- chest pain
- shortness of breath
- discomfort in your upper body
- Heart failure. Symptoms can include:
- shortness of breath
- extreme tiredness
- swelling in your legs, ankles, or feet
- unexpected weight gain
- Very fast heart rate
- Irregular heart rhythm
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Dosage for hypothyroidism
Adult dosage (ages 18–49 years):
- Your dosage will be based on several factors, including your age, weight, thyroid hormone levels, other conditions you have, and other medications you take. The typical dosage is 1.6 mcg/kg/day.
- Dosages are usually less than 200 mcg/day.
Child dosage (ages 0–17 years):
The dosage is based on weight and thyroid hormone levels.
Senior dosage (ages 50 years and older):
- The typical starting dosage is 12.5–25 mcg/day.
- Your doctor will adjust your dosage every 6–8 weeks, based on your thyroid hormone lab results.
Dosage for goiter
Adult dosage (ages 18 years and older):
Your dosage is based on your needs and thyroid hormone levels. Your doctor will determine the right dosage for you and adjust it based on your current level of thyroid hormone.
Child dosage (ages 0–17 years):
There are no dosage recommendations for people younger than 18 years.
Dosage for thyroid cancer
Adult dosage (ages 18 years and older):
Your dosage is based on your needs and thyroid hormone levels. Your doctor will determine the right dosage for you and adjust it based on your current level of thyroid hormone.
Child dosage (ages 0–17 years):
There are no dosage recommendations for people younger than 18 years.
Dosage for special populations
For pregnant women: You may need a higher dosage of levothyroxine.
For people with heart disease:
- The recommended starting dosage is 12.5–25 mcg/day.
- Your dosage may be adjusted every 6–8 weeks.
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