Levothyroxineليفوثيروكسين

Levothyroxine, sold under the brand name Euthyrox, is a thyroid hormone medicine used to replace or supplement the hormone when the thyroid gland doesn't produce enough of it.

Levothyroxine replaces the body's natural thyroid hormone. Thyroid hormone regulates many of the body's metabolic processes and plays a role in growth, development, and the maturation of the nervous system.

• Hypothyroidism, as replacement or supplementary treatment
• Suppressing thyroid-stimulating hormone (TSH) secretion from the pituitary gland, in certain thyroid conditions

Levothyroxine is not used for weight loss or obesity treatment — it is not effective for reducing weight, and using it in large doses for this purpose can cause serious or life-threatening harm, especially when combined with appetite-suppressant medicines.

Levothyroxine has a narrow therapeutic window — even a small increase or decrease in dose can meaningfully affect how well your thyroid levels are controlled, so it's important to follow your doctor's dosing instructions precisely and not adjust the dose on your own.

The dose is individualized and typically adjusted in steps of 12.5–25 micrograms until thyroid hormone levels (TSH) return to a normal, stable range.

Do not switch between different brands of levothyroxine without checking with your doctor first — different products may not work identically, even at the same labeled dose.

This is educational background, not an individual prescription — your own doctor sets and adjusts your exact dose based on regular blood tests.

Take on an empty stomach, about 30 minutes before breakfast, with a full glass of water.

• Store below 25°C
• Keep away from humidity and direct sunlight

• Headache
• Insomnia
• Nervousness, anxiety, or tremor
• Fever, hot flashes, or sweating
• Changes in menstrual periods
• Changes in appetite or weight
• Hair loss

Many of these can be signs the dose needs adjusting, so mention them to your doctor rather than adjusting the dose yourself.

Too much thyroid hormone can put strain on the heart. Seek medical attention immediately for chest pain (angina), a fast or irregular heartbeat, palpitations, shortness of breath, or facial flushing — these can be signs of a dose that's too high, or, rarely, more serious problems such as heart failure or a heart attack.

Long-term use of doses that are higher than needed has been linked to decreased bone mineral density, as well as muscle weakness or cramps. Regular monitoring helps keep the dose at the right level.

• Known hypersensitivity to levothyroxine or any component of the product
• Untreated thyrotoxicosis or overactive thyroid (hyperthyroidism)
• A low TSH level with normal T4/T3 levels, without further evaluation
• A recent heart attack
• Uncorrected adrenal insufficiency

Timing matters — take these several hours apart from levothyroxine

• Calcium supplements, iron supplements, and aluminum- or magnesium-containing antacids — these reduce how well levothyroxine is absorbed
• Cholestyramine or colestipol — separate by at least 2 hours
• Sucralfate — separate by at least 4 hours

Other noted interactions

• Warfarin (a blood thinner) — levothyroxine may increase its effect
• Tricyclic antidepressants — combined use may increase the toxicity of both medicines
• Ketamine — combined use can raise blood pressure and heart rate
• Digoxin and theophylline (heart/lung medicines) — their blood levels can change as thyroid levels change
• Estrogen — can reduce free thyroxine levels
• Imatinib (a cancer medicine) — can reduce how well levothyroxine works

Always tell your doctor and pharmacist about every other medicine and supplement you take.

Pregnancy: women with hypothyroidism need to keep taking levothyroxine during pregnancy — not treating it can cause problems for the baby, including miscarriage and preeclampsia. Thyroid levels (TSH) are generally checked at each prenatal visit and again 6–8 weeks after delivery, and the dose is often increased during pregnancy.

Breastfeeding: small amounts may pass into breast milk; a doctor should be consulted about use while breastfeeding.

• Regular blood tests (TSH, and sometimes T4) are needed to keep the dose at the right level
• Because of the narrow therapeutic window, don't skip follow-up appointments or stop the medicine without medical advice
• Do not switch between different brands or manufacturers without checking with your doctor first