Thyroid hormone replacement
Levothyroxine and grapefruit: a real interaction?
Grapefruit is famous as the juice that interacts with medications, and the warning is real for a number of drugs. Whether it matters specifically for Levothyroxine (Levothyroxine) at 25mcg, 50mcg, 75mcg, 100mcg, 150mcg depends on whether the active ingredient Levothyroxine is metabolised by CYP3A4 in the gut wall and how much that pathway contributes to first-pass metabolism.
The CYP3A4 mechanism
Grapefruit (and its juice) inhibits CYP3A4 enzymes in the gut wall, increasing the absorbed dose of medications metabolised by that enzyme. For drugs in the Thyroid hormone replacement class that go through CYP3A4 first-pass metabolism, regular grapefruit consumption can raise plasma levels of Levothyroxine by a clinically meaningful margin and amplify side effects.
What to do with Levothyroxine
According to the prescribing information for Levothyroxine, if grapefruit is flagged as an interaction, the safest practice is to avoid grapefruit entirely or to discuss timing with the prescriber. Levothyroxine replaces deficient endogenous thyroxine, which is converted in tissues to the active hormone triiodothyronine (T3) by deiodinase enzymes. A small occasional serving may be tolerable; daily large servings around the time of Levothyroxine dosing are not recommended at 25mcg, 50mcg, 75mcg, 100mcg, 150mcg.
Frequently asked questions
Can I eat grapefruit while on Levothyroxine? ▾
For some Thyroid hormone replacement medications, grapefruit is best avoided or limited because of CYP3A4 inhibition. Whether Levothyroxine specifically is affected depends on Levothyroxine; the prescribing information lists this. When in doubt, ask the pharmacist or check the patient leaflet.
How much grapefruit is too much with Levothyroxine? ▾
For drugs where the interaction matters, even modest daily grapefruit intake (one whole grapefruit or one large glass of juice) can shift drug levels noticeably. For Levothyroxine at 25mcg, 50mcg, 75mcg, 100mcg, 150mcg, individual tolerance varies; the cautious choice is to avoid grapefruit if any interaction is mentioned.
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.