Thyroid hormone replacement
Levothyroxine drug interactions: a practical overview
Drug interactions are the single biggest cause of preventable medication problems. Levothyroxine (Levothyroxine) interacts to varying degrees with several classes of medication and with a smaller list of foods. This page summarises the practically important ones at 25mcg, 50mcg, 75mcg, 100mcg, 150mcg, framed for a real-world prescription review rather than an exhaustive PDF list.
High-priority interactions for Levothyroxine
For Levothyroxine, the most clinically relevant interactions are typically with strong CYP3A4 inhibitors and inducers, with cardiovascular medications (notably nitrates for several Thyroid hormone replacement agents), with central nervous system depressants, and with medications affecting blood pressure or heart rate. Levothyroxine replaces deficient endogenous thyroxine, which is converted in tissues to the active hormone triiodothyronine (T3) by deiodinase enzymes.
Working with the pharmacist
A pharmacist review of all current medications is the practical safeguard against unintended interactions with Levothyroxine. According to the prescribing information for Levothyroxine, the full medication list — prescription, OTC, supplements and recreational substances — should be reviewed before starting and at every dose change at 25mcg, 50mcg, 75mcg, 100mcg, 150mcg.
Frequently asked questions
What's the most important Levothyroxine interaction to know? ▾
For most Thyroid hormone replacement medications, the highest-priority interaction is with nitrate medications used for chest pain — this combination is often a hard contraindication. After that, strong CYP3A4 inhibitors (some antifungals, macrolides) are the next concern at routine 25mcg, 50mcg, 75mcg, 100mcg, 150mcg doses.
Do I need to tell the pharmacist about supplements? ▾
Yes. Supplements and herbal products can interact with Levothyroxine in ways that prescription drug-drug interaction databases miss. The pharmacist needs the complete picture — including supplements like St John's Wort, grapefruit-containing products and high-dose vitamins — to flag risks at 25mcg, 50mcg, 75mcg, 100mcg, 150mcg.
Products containing Levothyroxine
More on Levothyroxine
- With alcoholLevothyroxine and alcohol — is it safe to drink?
- With foodShould Levothyroxine be taken with food?
- Side effectsLevothyroxine side effects: common, rare and warning signs
- Dosage guideLevothyroxine dosage guide: how much to take and when
- OnsetHow fast does Levothyroxine start working?
- DurationHow long does Levothyroxine last?
The information on this website is provided for reference and educational purposes only. It does not replace consultation with a qualified healthcare professional.