Thyroid Medication Management
Thyroid medication — primarily levothyroxine — interacts with several common drugs and supplements. Managing these interactions is essential for stable control.
This page covers the key considerations.
Last medically reviewed: 1 November 2025
Common interactions
Drugs that reduce levothyroxine absorption include calcium carbonate, iron supplements, antacids (aluminium/magnesium), sucralfate, cholestyramine, and sevelamer — separate by 4 hours. Proton pump inhibitors may also reduce absorption.
Drugs that increase thyroid hormone requirements include estrogen-containing medications, rifampicin, carbamazepine, phenytoin, and some others — dose adjustment may be needed.
Amiodarone affects thyroid function directly — thyroid monitoring is essential.
Supplements and foods
Calcium and iron supplements are the most common culprits — take them at least 4 hours apart from levothyroxine. Soy products, high-fibre diets, coffee, and grapefruit can affect absorption.
Biotin (vitamin B7) interferes with thyroid lab assays — stop biotin 2–3 days before testing if recommended by your lab.
Special situations
Pregnancy increases levothyroxine requirements by ~30% — dose adjustment and close TSH monitoring are essential. Elderly patients and those with heart disease start at lower doses and titrate slowly.
Surgery, acute illness, and major weight changes may require temporary dose adjustments.
Frequently asked questions
Do I need to tell my doctor about all medications?
Yes — always disclose all prescription drugs, over-the-counter medications, and supplements. Interactions are common and manageable with proper timing.
Can I take levothyroxine with coffee?
Wait at least 30–60 minutes after levothyroxine before coffee — it can reduce absorption. Many patients find bedtime dosing easier.
Does metformin affect thyroid medication?
Metformin may slightly lower TSH in some patients — usually not clinically significant, but thyroid function should be monitored if doses change.
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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