Synthroid

Generic name: Levothyroxine sodium

What is Synthroid?

Synthroid is a synthetic thyroid hormone that is used if your own thyroid gland is not making enough hormone; if you have an enlarged thyroid (a goiter) or are at risk of developing a goiter; if you have certain cancers of the thyroid; or if your thyroid production is low due to surgery, radiation, certain drugs, or disease of the pituitary gland or hypothalamus in the brain.

What is the most important information I should know about Synthroid?

If you are taking Synthroid to make up for a lack of natural hormone, it is important to take it regularly at the same time every day. You will probably need to take it for the rest of your life.

Who should not take Synthroid?

Do not take Synthroid if you are sensitive to thyroid hormone; if your thyroid gland is making too much thyroid hormone; if you have had a recent heart attack; or if your adrenal glands are not making enough corticosteroid hormone. If you are sensitive to dyes, you can take the Synthroid 50-microgram tablet, which is made without color additives.

Although Synthroid will speed up your metabolism, it is not effective as a weight-loss drug and should not be used as such. An overdose may cause life-threatening side effects, especially if you take Synthroid with an appetite-suppressant medication.

What should I tell my doctor before I take the first dose of Synthroid?

Tell your doctor about all prescription, over-the-counter, and herbal medications you are taking before beginning treatment with Synthroid. Also, talk to your doctor about your complete medical history, especially if you have: a history of blood clots, anemia (lack of red blood cells), angina (chest pain caused by a heart condition), diabetes, heart disease, high blood pressure, problems with your pituitary or adrenal glands, seizures.

What is the usual dosage?

The information below is based on the dosage guidelines your doctor uses. Depending on your condition and medical history, your doctor may prescribe a different regimen. Do not change the dosage or stop taking your medication without your doctor's approval.

Adults: The average full replacement dose of Synthroid is approximately 1.7 micrograms (mcg) per 2.2 pounds of body weight per day (eg, 100 to 125 mcg/day for a 154-pound adult). Older patients may require less than 1 mcg per 2.2 pounds of body weight per day.

Infants and Children: The usual recommended dose is based on body weight and decreases with age. For severe hypothyroidism, a starting dose of 25 mcg/day is recommended with increments of 25 mcg every 2-4 weeks until the desired effect is achieved.

Newborns: The recommended starting dose of Synthroid in newborn infants is 10 to 15 mcg per 2.2 pounds of body weight per day. A lower starting dose (eg, 25 mcg/day) may be given if your infant is at risk for heart failure; the dose should be increased in 4 to 6 weeks as needed based on your baby's response. If your newborn has very low amounts of thyroid hormone (serum T₄ concentrations), the recommended starting dose is 50 mcg/day.

How should I take Synthroid?

Take Synthroid as a single dose, preferably on an empty stomach, 30 minutes to 1 hour before breakfast. The drug is absorbed better on an empty stomach.

Take your daily dose of Synthroid at least 4 hours apart from taking any other medicines, supplements, or foods that may interact with Synthroid.

Synthroid tablets may swell quickly, resulting in choking or gagging. Be sure to take the pills with an entire glass of water to avoid this problem.

If an infant or child cannot swallow whole tablets, you may crush a Synthroid tablet and mix it into 1 to 2 teaspoonfuls of water. The suspension can be administered by spoon or by dropper. DO NOT STORE THE SUSPENSION.

Foods that decrease absorption of Synthroid, such as soybean infant formula, should not be used for administering Synthroid.

What should I avoid while taking Synthroid?

Do not stop taking Synthroid or change the way you take it unless your doctor tells you to do so. Do not stop taking Synthroid even if you feel fine. Stopping the medicine could lead to other health conditions, such as infertility, problems during pregnancy, and heart disease.

Do not change brands or change to a generic levothyroxine drug product without first asking your doctor. Different brands may not work in the same way.

Walnuts, dietary fiber, antacids, and iron and calcium supplements can decrease the amount of Synthroid your body absorbs. Take Synthroid at least 4 hours apart from these other food and medicines.

What are possible food and drug interactions associated with Synthroid?

If Synthroid is taken with certain other drugs, the effects of either could be increased, decreased, or altered. It is especially important to check with your doctor before combining Synthroid with the following: amiodarone, androgens (male hormones), antacids and antigas medications, antidepressants such as imipramine and sertraline, blood pressure drugs, blood-thinners such as heparin and warfarin, cancer drugs (such as 5-fluorouracil, 6-mercaptopurine, mitotane, and tamoxifen), chloral hydrate, cholesterol-lowering drugs, diabetes drugs such as glyburide and insulin, digoxin, estrogen products and oral contraceptives, furosemide, growth hormones, hormone inhibitors such as aminoglutethimide and methimazole, interferon, interleukin, iodide, iron supplements, kayexalate, ketamine, lithium, methadone and heroin, metoclopramide, nonsteroidal anti-inflammatory drugs such as ibuprofen and naproxen, Parkinson's drugs such as levodopa/carbidopa, propylthiouracil, seizure medications such as carbamazepine, phenobarbital, and phenytoin, steroids such as dexamethasone and hydrocortisone, stimulants such as epinephrine, sucralfate, tranquilizers, tuberculosis drugs, theophylline.

What are the possible side effects of Synthroid?

Side effects cannot be anticipated. If any develop or change in intensity, tell your doctor as soon as possible. Only your doctor can determine if it is safe for you to continue taking this drug.

Side effects may include: allergic reactions such as rash or hives, changes in appetite, initial and usually temporary hair loss, fatigue, headache, heat intolerance, diarrhea, vomiting, menstrual irregularities

In rare cases, infants taking Synthroid may experience increased pressure in the skull. Seizures are another rare side effect of Synthroid.

Excessive dosage or too rapid of an increase in dosage may lead to over-stimulation of the thyroid gland.

Can I receive Synthroid if I am pregnant or breastfeeding?

If you need to take Synthroid because of a thyroid hormone deficiency, you can continue to take Synthroid during pregnancy. In fact, your doctor will test you regularly and may increase your dose. Once your baby is born, you may breastfeed while continuing to take carefully regulated doses of Synthroid, unless your doctor says otherwise.

What should I do if I miss a dose of Synthroid?

Take it as soon as you remember that day. If you do not remember until the next day, or if you miss more than one dose, call your doctor for advice on what you should do.

How should I store Synthroid?

Store at room temperature, away from light and moisture. Keep in a tightly closed container.