What is the standard starting dose of levothyroxine?

For healthy adults with overt hypothyroidism, the standard starting estimate is **1.6 mcg/kg/day**, rounded to the nearest available tablet strength. For a 70 kg adult this is approximately *112 mcg/day*. Elderly and cardiac patients must start much lower — typically *12.5–25 mcg/day*.

How long does it take for levothyroxine to work?

Symptoms of hypothyroidism typically begin to improve within **4–6 weeks** of starting or adjusting the dose. Full symptomatic and biochemical stabilisation may take *3–6 months*. TSH should be checked 4–6 weeks after each dose change.

Why does pregnancy increase the levothyroxine requirement?

Pregnancy increases thyroid hormone demand due to *fetal thyroid requirements*, increased thyroid-binding globulin, and placental degradation of T4. The dose typically needs to increase by **30–50%** from the pre-pregnancy level, often as soon as pregnancy is confirmed.

Why should levothyroxine be taken on an empty stomach?

Food, coffee, and dairy products *significantly reduce absorption* of levothyroxine. Taking it *30–60 minutes before breakfast* on an empty stomach ensures consistent and maximal absorption, which is critical for maintaining stable TSH levels.

What TSH should I aim for on levothyroxine?

For most adults, the treatment target is a **TSH within the normal reference range** (typically 0.4–4.0 mU/L). Some clinicians target the *lower half of the range* (0.5–2.0 mU/L) for better symptom control. Intentional TSH suppression is only appropriate in specific thyroid cancer management protocols.

Can levothyroxine cause heart problems?

At excessive doses, levothyroxine can cause *tachycardia, palpitations, atrial fibrillation*, and worsening of *angina* — particularly in elderly patients and those with pre-existing cardiac disease. This is why these groups must be started at very low doses and titrated slowly under close supervision.

Do I need to take levothyroxine for life?

For most causes of primary hypothyroidism, including *Hashimoto's thyroiditis* and post-surgical hypothyroidism, levothyroxine is **lifelong therapy**. In a minority of patients (e.g., drug-induced or transient hypothyroidism), the requirement may resolve — reassessment with the prescriber is warranted.

Endocrinology · Hormone Therapy

TSH Levothyroxine
Dose Calculator

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TSH — Levothyroxine Dose Calculator

Educational tool · Last reviewed: March 2026

This tool provides weight-based starting dose estimates for levothyroxine. These are population-level starting points only.

Actual doses must be individualised based on clinical response, serial TSH monitoring, symptoms, and comorbidities. Doses should be titrated gradually with regular laboratory review.

Always confirm dosing with the treating clinician and follow local guidelines. Recheck TSH approximately 6–8 weeks after any dose change.

I understand this is educational only and will verify dosing with the treating clinician.