Levothyroxine – Essential thyroid hormone replacement therapy.
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What is Levothyroxine?
Levothyroxine is a synthetic thyroid hormone that’s essential for people with hypothyroidism (underactive thyroid). It replaces the hormone your thyroid gland cannot produce sufficiently, helping restore normal energy levels, metabolism, and overall wellbeing.
Book an online consultation if you’re experiencing symptoms of hypothyroidism such as fatigue, weight gain, feeling cold, depression, or slow heart rate. Our GPs can arrange appropriate blood tests and thyroid function monitoring to determine if Levothyroxine treatment is needed.
What is Levothyroxine used for?
- Hypothyroidism (underactive thyroid)
- Thyroid hormone replacement after thyroidectomy
- Goiter treatment and prevention
- Thyroid suppression therapy
- Congenital hypothyroidism in children
- Subclinical hypothyroidism (in some cases)
How does Levothyroxine work?
A synthetic form of thyroxine (T4) that replaces the natural thyroid hormone your body cannot produce sufficiently, restoring normal metabolic function and energy levels.
Dosage and Administration
Adults
Starting dose usually 50-100 micrograms daily, adjusted based on blood tests. Maintenance typically 100-200 micrograms daily.
Children
Dose calculated based on weight and age—specialist pediatric supervision required.
Important Notes
- Take on an empty stomach, 30-60 minutes before breakfast.
- Take at the same time each day for consistent levels.
- Avoid taking with coffee, calcium, or iron supplements.
- Regular blood tests needed to monitor and adjust dose.
Side Effects
Common Side Effects
- Initially may cause no side effects if dose is appropriate
- Temporary hair loss (usually improves with time)
- Weight changes as metabolism adjusts
- Mood changes during dose adjustment
Serious Side Effects
Seek immediate medical attention if you experience:
- Chest pain or heart palpitations (overdose signs)
- Severe headaches
- Tremor and excessive sweating
- Insomnia and anxiety
- Bone thinning with long-term overdosing
- Heart rhythm problems
Important Warnings
- Never stop taking suddenly—can cause severe hypothyroid symptoms.
- Dose must be individualized based on regular blood tests (TSH levels).
- Tell your GP if you have heart disease—dose increases must be gradual.
- Many medications and supplements can affect absorption.
- Pregnancy may require dose adjustments—regular monitoring needed.
Drug Interactions
Tell your GP if you're taking any of the following medications:
- Iron supplements—take 4 hours apart from Levothyroxine.
- Calcium supplements—take 4 hours apart from Levothyroxine.
- Coffee—may reduce absorption, take medication first.
- Warfarin—may enhance anticoagulant effects.
- Antacids and PPIs—may reduce Levothyroxine absorption.
- Cholestyramine—significantly reduces absorption.
Frequently Asked Questions
Why must I take Levothyroxine on an empty stomach?
Food, especially calcium and iron, can significantly reduce absorption. Taking it on an empty stomach ensures consistent and maximum absorption.
How long before I feel better on Levothyroxine?
Most people start feeling improvements within 2-4 weeks, but it can take 6-8 weeks to reach full benefits as your body adjusts to normal thyroid levels.
What happens if I miss doses regularly?
Missing doses can cause hypothyroid symptoms to return (fatigue, weight gain, depression). If you miss a dose, take it as soon as remembered unless it's nearly time for the next dose.
Do I need to take Levothyroxine forever?
Most people with hypothyroidism need lifelong treatment. However, some cases (like postpartum thyroiditis) may be temporary and require only short-term treatment.
Medically Reviewed by: Mohammed Hassan - Independent Prescriber
Last Updated: 2025-01-14