Loading
If this is the first time anyone has visited this substance, we may be fetching live data from TGA Product Information, PBS, and state framework sources — that can take up to a minute. Cached substances load in a second or two.
A plain-language summary of the cited sources below. Informational only — not medical advice.
Levothyroxine is a synthetic version of thyroxine, a hormone normally made by the thyroid gland. It's prescribed when someone's thyroid isn't producing enough hormone on its own. The thyroid hormones control how quickly the body uses energy — they affect heart rate, body temperature, and how food is converted into fuel.
The medication works as a replacement. Once taken, levothyroxine converts in the body to a more active form called T3, which enters cells and switches on genes that control metabolism. Because the body processes levothyroxine slowly — it has a half-life of about seven days — it builds up gradually and stays steady in the bloodstream. That's why dosing is typically once daily and changes take weeks to show effect.
Common side effects include headache, tremors, palpitations, sweating, and weight loss. These often signal the dose is too high for the person's needs. Serious reactions are uncommon but include heart problems such as myocardial infarction and cardiac failure, seizures, severe allergic reactions, and in rare cases death. The medication should not be used in people with untreated overactive thyroid, uncorrected adrenal gland problems, acute heart attack unrelated to low thyroid, or acute inflammation of the heart muscle or surrounding tissue. It's also not suitable for people with known allergy to thyroxine. During pregnancy, levothyroxine must not be combined with medications that suppress thyroid activity.
If your family member has been prescribed levothyroxine, their doctor will monitor thyroid hormone levels with blood tests to find the right dose. Too little and the original symptoms persist; too much and the side effects listed above may appear.
For prescribing by certain health practitioners Clinical criteria: Treatment criteria: Must be treated by a health practitioner who is any of: (i) a medical practitioner, (ii) a nurse practitioner, (iii) an endorsed midwife who is each of: (a) sharing patient care with a medical practitioner for the current pregnancy episode, (b) continuing existing treatment with this drug that was initiated by a medical practitioner.
“The principal pharmacological effect of thyroid hormones is to increase the metabolic rate of body tissues.”
“Levothyroxine sodium has a plasma half-life in euthyrodism of about 6 to 7 days. In hypothyroidism, the half life is prolonged between 9 to 10 days.”
A plain-language summary of the cited sources below. Informational only — not medical advice.
Levothyroxine is a synthetic T4 thyroid hormone indicated for the management of demonstrated thyroid hormone deficiency and for suppression of thyrotropin in TSH-responsive thyroid tumours. It functions as a prohormone: peripheral conversion by iodothyronine deiodinase yields T3, which binds thyroid receptor proteins in the cell nucleus to regulate DNA transcription, protein synthesis, and metabolic rate. The principal pharmacological effect is increased metabolic rate of body tissues.
The plasma half-life in euthyroid individuals is approximately six to seven days, prolonged to nine to ten days in hypothyroidism and shortened to three to four days in hyperthyroidism. Common adverse effects include headache, tremor, palpitations, sweating, and weight loss. Serious adverse effects—myocardial infarction, cardiac failure, seizures, anaphylactic reactions, and death—have been reported. Contraindications include known hypersensitivity, untreated hyperthyroidism, uncorrected adrenal insufficiency, thyrotoxicosis, acute myocardial infarction uncomplicated by hypothyroidism, acute myocarditis, acute pancarditis, and combination use with antithyroid agents during pregnancy for the treatment of hyperthyroidism.
Working under the parallel aged-care framework? Aged-care equivalent →
Curated subset. The full adverse-effect list is in the TGA Product Information; click any citation above to open it.