Some prescription medications interact with grapefruit or grapefruit juice. Most do not, however, and there is no evidence that thyroid medicines interact with grapefruit. But to be sure you understand any possibly interactions with medications you take, read the Gradon's Guide to Grapefruit Interactions or Grapefruit Drug Interactions Website.
I have read reference to grapefruit juice effecting the absorption of L-thyroxine.
These are medications with which grapefruit juice should NOT be consumed unless advised by a doctor:
* Statins (cholesterol drugs): lovastatin (Mevacor), atorvastatin Lipitor, simvastatin Zocor, simvastatin/ezetimibe (Vytorin)
* Antihistamines: fexofenadine (Allegra), (terfenadine (Seldane), taken off the U.S. market
* Calcium channel blockers (blood pressure drugs): nimodipine (Nimotop), felodipine (Nitrendipine, Plendil), nisoldipine (Sular), nicardipine (Cardene), verapamil (Verelan)
* Psychiatric medications: buspirone (BuSpar), triazolam (Halcion), carbamazepine (Tegretol), diazepam (Valium), midazolam (Versed), sertraline (Zoloft)
* Intestinal medications: cisapride (Propulsid) taken off the U.S. market
* Immune suppressants: cyclosporine (Neoral), (tacrolimus) Prograf
* Pain medications: Methadone
* Impotence drug: (erectile dysfunction): sildenafil (Viagra)
* HIV medication: saquinavir (Invirase, Fortovase)
* Antiarrhythmics: amiodarone (Cordarone), disopyramide (Norpace)