Levothyroxine Treatment
Levothyroxine is a synthetic form of thyroxine (T4) — the hormone the thyroid normally produces. It is the established, evidence-based treatment for hypothyroidism and is used worldwide.
This page provides general education — dosing and prescriptions require a qualified clinician.
Last medically reviewed: 1 November 2025
Key points
- Levothyroxine replaces thyroid hormone in hypothyroidism.
- Take it on an empty stomach, 30–60 minutes before food.
- The dose is adjusted by TSH testing, usually 6–8 weeks after a change.
- Most people need lifelong treatment.
How it works
Levothyroxine replaces the missing T4. The body converts some T4 to the more active T3 as needed. Because T4 has a long half-life (~7 days), levels stay stable with once-daily dosing — unlike shorter-acting hormones.
It does not cure the underlying cause (usually Hashimoto’s) but restores normal hormone levels and resolves symptoms.
Taking it correctly
Levothyroxine is best absorbed on an empty stomach — typically 30–60 minutes before breakfast, or at bedtime (separated from the last meal by several hours). Consistency matters more than the exact time.
Several substances interfere with absorption: calcium, iron, antacids, soy, coffee, and some medications should be separated by several hours. Your doctor or pharmacist will advise on timing.
Dosing and monitoring
Dosing is individualised by weight, age, cardiac status and TSH response. After starting or changing dose, TSH is rechecked every 6–8 weeks until stable, then periodically.
Symptoms of under-replacement (fatigue, cold intolerance, weight gain) or over-replacement (palpitations, anxiety, insomnia, weight loss) prompt dose review — never adjust dose without medical advice.
Long-term considerations
Most patients need lifelong treatment for primary hypothyroidism. Dose requirements may change with weight, age, pregnancy, and interacting medications.
Brand vs generic formulations can vary slightly — if switching brands causes symptom changes, discuss consistency with your prescriber.
Frequently asked questions
How long until levothyroxine starts working?
TSH begins improving within weeks; symptom relief typically follows over 4–12 weeks as hormone levels stabilise. Full benefit may take several months.
Can I take levothyroxine with other medications?
Yes, but timing matters — calcium, iron, antacids and some drugs reduce absorption. Separate them by at least 4 hours. Your pharmacist can advise.
What happens if I miss a dose?
Take it when remembered unless it is nearly time for the next dose — do not double up. Occasional missed doses are not dangerous; consistent missed doses affect control.
References & further reading
This page is based on established medical knowledge and guidelines from authoritative sources. Always consult a qualified clinician for personal medical advice.
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