Thyroid hormone should not be used to treat obesity in patients with normal thyroid function. Levothyroxine is ineffective for weight reduction in normal thyroid patients and may cause serious or life-threatening toxicity, especially when taken with amphetamines. Talk to your doctor about the potential risks associated with this medication.
Levothyroxine, a thyroid hormone, is used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone. Without this hormone, the body cannot function properly, resulting in: poor growth; slow speech; lack of energy; weight gain; hair loss; dry, thick skin; and increased sensitivity to cold. When taken correctly, levothyroxine reverses these symptoms. Levothyroxine is also used to treat congenital hypothyroidism (cretinism) and goiter (enlarged thyroid gland).
This medication is sometimes prescribed for other uses; ask your doctor or pharmacist for more information.
Levothyroxine comes as a tablet to take by mouth. It usually is taken once a day on an empty stomach, one half to one hour before breakfast. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take levothyroxine exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.
The tablets may get stuck in your throat or cause choking or gagging; therefore, the tablet should be taken with a full glass of water.
If you are giving levothyroxine to an infant or child who cannot swallow the tablet, crush the tablet and mix it in 1 to 2 teaspoons of plain water. Give this mixture by spoon or dropper right away. Do not store this mixture. Only mix the crushed tablets with water. Do not mix with food or soybean infant formula.
Your doctor will probably start you on a low dose of levothyroxine and gradually increase your dose.
Levothyroxine controls hypothyroidism, but does not cure it. It may take several weeks before you notice a change in your symptoms. Continue to take levothyroxine even if you feel well. Do not stop taking levothyroxine without talking to your doctor.
Before taking levothyroxine,
- tell your doctor and pharmacist if you are allergic to levothyroxine, thyroid hormone, any other drugs, povidone iodine, tartrazine (a yellow dye in some processed foods and drugs), or foods such as lactose or corn starch. Levothroid contains lactose, while Synthroid contains tartrazine and povidone.
- tell your doctor and pharmacist what prescription and nonprescription medications you are taking, especially amphetamines; anticoagulants ('blood thinners') such as warfarin (Coumadin); antidepressants or anti-anxiety agents; arthritis medicine; aspirin; beta-blockers such as metoprolol (Lopressor, Toprol), propranolol (Inderal) or timolol (Blocadren, Timoptic); cancer chemotherapy agents; diabetes medications (insulin and tablets); digoxin (Lanoxin); estrogens; methadone; oral contraceptives; phenytoin (Dilantin); steroids; theophylline (TheoDur); and vitamins.
- if you take an antacid, calcium carbonate (Tums), cholestyramine (Questran), colestipol (Colestid), iron, orlistat (alli, Xenical), simethicone (Phazyme, Gas X), sodium polystrene sulfonate (Kayexalate), or sucralfate (Carafate), take it at least 4 hours before or 4 hours after you take levothyroxine.
- tell your doctor if you have or have ever had diabetes; hardening of the arteries (atherosclerosis); kidney disease; hepatitis; cardiovascular disease such as high blood pressure, chest pain (angina), arrhythmias, or heart attack; or an underactive adrenal or pituitary gland.
- tell your doctor if you are pregnant, plan to become pregnant or are breast-feeding. If you become pregnant while taking levothyroxine, call your doctor.
- if you have surgery, including dental surgery, tell the doctor or dentist that you are taking levothyroxine.
Unless your doctor tells you otherwise, continue your normal diet.
Take the missed dose as soon as you remember it. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.
Levothyroxine may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:
- weight loss
- stomach cramps
- excessive sweating
- increased appetite
- changes in menstrual cycle
- sensitivity to heat
- temporary hair loss, particularly in children during the first month of therapy
If you experience either of the following symptoms, call your doctor immediately:
- chest pain (angina)
- rapid or irregular heartbeat or pulse
If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online [at Web Site] or by phone [1-800-332-1088].
Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom). Throw away any medication that is outdated or no longer needed. Talk to your pharmacist about the proper disposal of your medication.
In case of overdose, call your local poison control center at 1-800-222-1222. If the victim has collapsed or is not breathing, call local emergency services at 911.
Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests to check your response to levothyroxine.
Learn the brand name and generic name of your medication. Do not switch brands without talking to your doctor or pharmacist, as each brand of levothyroxine contains a slightly different amount of medication.
Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.
It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.
AHFS® Consumer Medication Information. © Copyright, The American Society of Health-System Pharmacists, Inc., 7272 Wisconsin Avenue, Bethesda, Maryland. All Rights Reserved. Duplication for commercial use must be authorized by ASHP.
Last Reviewed: September 1, 2010.