Levothyroxine is used to treat an underactive thyroid gland (hypothyroidism). It replaces or provides more thyroid hormone, which is normally produced by the thyroid gland. Low thyroid hormone levels can occur naturally or when the thyroid gland is injured by radiation/medications or removed by surgery. Having enough thyroid hormone is important for normal mental and physical activity. In children, having enough thyroid hormone is important for normal mental and physical development.
This medication is also used to treat other types of thyroid disorders (such as certain types of goiters, thyroid cancer).
This medication should not be used to treat infertility unless it is caused by low thyroid hormone levels.
Hair loss may occur during the first few months of treatment. This effect is usually temporary as your body adjusts to this medication. If this effect lasts or gets worse, tell your doctor or pharmacist promptly.
Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.
Tell your doctor right away if you have any serious side effects, including: increased sweating, sensitivity to heat, mental/mood changes (such as nervousness, mood swings), tiredness, diarrhea, shaking (tremor), headache, shortness of breath, bone pain, easily broken bones.
Get medical help right away if you have any very serious side effects, including: chest pain, fast/pounding/irregular heartbeat, swelling hands/ankles/feet, seizures.
A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.
This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.
Before taking levothyroxine, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.
Before using this medication, tell your doctor or pharmacist your medical history, especially of: increased thyroid hormones (thyrotoxicosis), decreased adrenal gland function, heart disease (such as coronary artery disease, irregular heartbeat), high blood pressure, diabetes.
If you have diabetes, this drug may affect your blood sugar. Check your blood sugar regularly as directed and share the results with your doctor. Tell your doctor right away if you have symptoms such as increased thirst/urination, shakiness, unusual sweating, dizziness, or hunger. Your doctor may need to adjust your diabetes medication, exercise program, or diet.
Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).
Children may be more sensitive to certain side effects of this drug, especially headache, vision changes, and hip/leg pain. High thyroid hormone levels may lead to decreased bone development/growth and reduced final adult height. Keep all lab/medical appointments so the doctor can monitor treatment.
Older adults may be more sensitive to the side effects of this drug, especially fast/pounding/irregular heartbeat.
This drug may be used during pregnancy. Tell your doctor if you are pregnant because your doctor may need to change your dose.
Levothyroxine passes into breast milk but is unlikely to harm a nursing infant. Consult your doctor before breast-feeding.