Ideally Synthroid™ (levothyroxine) should be taken on an empty stomach in order to keep blood levels the same on a day to day basis. In the past the empty stomach rule was more or less a "suggestion" and it was just important to take it the same way (ie. with the same meds, or with a similar breakfast) every day.

I believe that the main reason that recent recommendations say to take the drug on an empty stomach is that the new pharmacy software programs (eg. Kroll Windows) print out little stickers saying to take it on an empty stomach (1 hour before or two hours after meals or other medication). To tell you the truth, I never put "empty stomach" warnings on Synthroid prescriptions until the software told me to. I always counseled just to take the medication the same way every day. There is a certain amount of leeway for blood levels of the drug, and the periodic assessment of thyroid status by blood tests give a, more or less, reasonable indication of what dose one should be taking.

That said, there are many medications and situations that will affect levels of Synthroid in the blood. The magnitude and relative clinical importance of drug interactions are likely to be patient-specific and may vary by such factors as age, gender, race, intercurrent illnesses, dosages of other drugs being taken (especially ones added or stopped), as well as timing of taking these other medications in relation to the taking of the Synthroid. Dosage adjustments may have to be made if you start or stop any of the following medications (Note: the list is long, but not all inclusive).

Certain medications will bind to Synthroid and decrease it's absorption from the intestine. Some of these are: aluminum hydroxide (in Maalox™, Diovol™, Gaviscon™, Mylanta™, etc.); cholestyramine resin (Questran™); colestipol (Colestid™); ferrous sulfate (Fer-In-Sol™); sodium polystyrene sulfonate (Kayexalate™), soybean flour (in certain infant formulas); and sucralfate (Sulcrate™).

Other medications may affect Synthroid's binding to plasma proteins or alter the concentration of plasma proteins, which may affect Synthroid's half-life (how long the drug remains active in the body). Some of these being androgens and related anabolic hormones (fluoxymesterone - Halotestin™; nandrolone - Durabolin™; and testosterones - Climacteron™, Androderm™, Androgel™, Testoderm™, Andriol™, Delatestryl™); l-asparaginase (Elspar™, Kidrolase™); clofibrate (Atromid-S™); estrogens (Premarin™, Estrace™, Estraderm™, Estrogel™, etc.); 5-fluorouracil (Adrucil™, Efudex™); furosemide (Lasix™); glucocosteroids (prednisone, cortisone, dexamethasone, etc.); meclofenamic acid (Meclomen™); mefenamic acid (Ponstan™, Ponstel™); methadone (Metadol™, Methadose™); perphenazine (Trilafon™, Etrafon™, Triavil™); phenylbutasone, phenytoin (Dilantin™); salicylates (Aspirin™, etc.); and tamoxifen (Nolvadex™, Tamofen™).

Other drugs can alter thyroid hormone or TSH levels by effects on thyroid hormone synthesis, secretion, distribution, metabolism, hormone action, or elimination, or TSH secretion: p-aminosalicylic acid (Nemasol Sodium™); amiodarone (Cordarone™); antithyroid drugs (methimazole - Tapazole™, propylthiouracil (Propyl-Thyracil™); beta-blockers (propranolol - Inderal™; atenolol - Tenormin™; bisoprolol - Monocor™, Zebeta™; metoprolol - Betaloc™, Lopressor™; etc.); carbamazepine (Tegretol™); chloral hydrate (Noctec™); dopamine (Intropin™), dopamine agonists (bromocriptine - Parlodel™; pergolide - Permax™; pramipexole - Mirapex™; ropinirol - ReQuip™); ethionamide (Trecator-SC™); heparin (Hepalean™); insulin (Humulin™, Novolin™); iodine-containing compounds, levodopa (Sinemet™, Prolopa™, Dopar™, Larodopa™); lovastatin (Mevacor™); lithium (Carbolith™, Duralith™, Lithane™); 6-mercaptopurine (Purinethol™); metoclopramide (Maxeran™, Reglan™); mitotane (Lysodren™); nitroprusside (Nitropres™); phenobarbital (Donnatal™, Phenaphen™, Bellergal Spacetabs™); rifampin (Rifadin™, Rofact™, Rifamate™, Rifater™), somatostatin (Stilamin™); sulfonamides (sulfamethoxazole - Gantanol™, Bactrim™, Septra™; sulfamethizole - Thiosulfil™; sulfanilamide - AVC™; sulfamethazine - Trisulfaminic™; sulfadiazine - Coptin™); sulfonylureas (chlorpropamide - Diabinese™; gliclazide - Diamicron™; glyburide - Diabeta™; tolbutamide); and thiazide diuretics (chlorthalidone - Tenoretic™, Regroton™; hydrochlothiazide - HydroDiuril™, Ziac™, Inhibace Plus™, Prinizide™, Zestoretic™, Hyzaar™, Uniretic™, Vaseretic™, Avalide™, Oreticyl™, Captozide™,Accuretic™, Viskazide™, Inderide™, Aldactazide™, Timolide™, etc.; indapamide - Lozide™, Lozol™; metolazone - Zaroxolyn™, Mykrox™).

Various others: interferon (Roferon™, Intron™, Rebetron™, Avonex™, Rebif™, Actimmune™, etc.); digitalis glycosides (digoxin - Lanoxin™, Lanoxicaps™); ketamine (Ketalar™); maprotiline (Ludiomil™); theophylline (Theo-Dur™, Uniphyl™, Theolair™, etc.); tricyclic antidepressants (amitriptyline - Elavil™, Endep™; nortriptyline - Aventyl™, etc.; desipramine - Nopramin™, etc.; imipramine - Tofranil, etc.; etc, etc, etc.), and many others.

Sorry, I got tired looking up the different drugs, but I think I got most of them. This list is probably why they say, "Take Synthroid On An Empty Stomach". Seriously, taking Synthroid by itself will give you better blood levels and probably you can be maintained on a lower dose than if you took it with food or other medications. Just keep in mind that any medication regimen change, or change in dosage of current medications, may necessitate a check of your thyroid levels, and perhaps even a change in Synthroid dose. Ask your doctor about this when making medication changes.

I hope that this is of some help. - Cam