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The commonly used oral prescription medication levothyroxine (EUTHYROX, LEVOLET, LEVO-T, LEVOXYL, SYNTHROID, THYQUIDITY, THYRO-TABS, TIROSINT, TIROSINT-SOL, UNITHROID) is chemically identical to the human thyroid hormone thyroxine.[1] It is taken once daily, primarily to treat hypothyroidism (underactive thyroid gland).
Generally, levothyroxine absorption is increased by fasting and decreased with aging and malabsorption conditions. Importantly, a wide range of prescription and...
The commonly used oral prescription medication levothyroxine (EUTHYROX, LEVOLET, LEVO-T, LEVOXYL, SYNTHROID, THYQUIDITY, THYRO-TABS, TIROSINT, TIROSINT-SOL, UNITHROID) is chemically identical to the human thyroid hormone thyroxine.[1] It is taken once daily, primarily to treat hypothyroidism (underactive thyroid gland).
Generally, levothyroxine absorption is increased by fasting and decreased with aging and malabsorption conditions. Importantly, a wide range of prescription and over-the-counter medications, dietary supplements and even certain foods can impact the absorption or effectiveness of levothyroxine when used concomitantly (at the same time) with it. To a lesser extent, levothyroxine can alter the effects of other medications as well. We discuss these interactions below to help levothyroxine users recognize and avoid impairment in their drug treatment.
Drugs and supplements that impact levothyroxine
By far, most drug interactions with levothyroxine involve impairment of its absorption or therapeutic effect.[2] The Table below lists numerous oral drugs that may result in such interactions when used concomitantly with levothyroxine. These drugs include bile acid sequestrants used to lower cholesterol levels in the blood (such as colesevelam [WELCHOL]); Levothyroxineproton pump inhibitors used to suppress stomach acid (such as esomeprazole [NEXIUM]); ion-exchange resins used to lower blood levels of potassium (such as patiromer [VELTASSA]) or phosphate (such as lanthanum [FOSRENOL]); menopausal hormone drugs (such as conjugated estrogens [PREMARIN]); the seizure medication phenytoin (DILANTIN, PHENYTEK); and certain antibiotics (such as ciprofloxacin [CIPRO]).
In addition, the concomitant use of aluminum-, calcium- or magnesium-containing antacids used to treat heartburn and certain dietary supplements that contain iron, calcium and chromium, as well as the over-the-counter colic medication simethicone (INFACOL), can decrease the absorption or effectiveness of levothyroxine.[3] Certain herbs (including bugleweed and Lithospermum) also appear to reduce the effectiveness of levothyroxine.
In contrast, the absorption of levothyroxine is enhanced when it is taken with vitamin C.[4] Moreover, the diabetes drug semaglutide (RYBELSUS) may increase levothyroxine blood levels.
Examples of Oral Drugs That May Decrease the Absorption or Effectiveness of Levothyroxine When Used Concomitantly[5],[6]
| Generic Name | Brand Name(s)† | Drug Class |
|---|---|---|
| aluminum hydroxide | AMPHOJEL | Antacid |
| amiodarone* | PACERONE | Abnormal heart rhythm drug |
| calcium carbonate | CAL-GEST ANTACID, TUMS | Antacid |
| chloroquine* | generic only | Antimalarial drug |
| cholestyramine | LOCHOLEST, PREVALITE | Bile acid sequestrant |
| ciprofloxacin* | CIPRO | Antibiotic |
| colesevelam | WELCHOL | Bile acid sequestrant |
| colestipol | COLESTID | Bile acid sequestrant |
| conjugated estrogens* | PREMARIN | Menopausal hormone therapy drug |
| dexlansoprazole* | DEXILANT | Proton pump inhibitor |
| esomeprazole* | NEXIUM | Proton pump inhibitor |
| esterified estrogens* | MENEST | Menopausal hormone drug |
| estradiol* | generic only | Menopausal hormone drug |
| estramustine | EMCYT | Prostate cancer drug |
| estropipate | OGEN 5 | Menopausal hormone drug |
| ferrous sulfate | FEOSOL | Iron-deficiency anemia drug |
| imatinib | GLEEVEC | Chemotherapy drug |
| lansoprazole* | PREVACID | Proton pump inhibitor |
| lanthanum | FOSRENOL | Phosphate binder |
| lopinavir | KALETRA | Antiviral drug for HIV infection |
| omeprazole* | PRILOSEC | Proton pump inhibitor |
| orlistat** | XENICAL, ALLI | Weight-loss drug |
| pantoprazole* | PROTONIX | Proton pump inhibitor |
| patiromer | VELTASSA | Potassium binder |
| phenytoin | DILANTIN, PHENYTEK | Antiseizure medication |
| rabeprazole* | ACIPHEX | Proton pump inhibitor |
| raloxifene*** | EVISTA | Selective estrogen receptor modulator |
| rifampin | RIFADIN, RIMACTANE | Antibiotic |
| ritonavir | NORVIR | Antiviral drug for HIV infection |
| sertraline* | ZOLOFT | Selective serotonin reuptake inhibitor antidepressant |
| sevelamer | RENAGEL, RENVELA | Phosphate binder |
| simethicone** | GENASYME, MYLICON | Gas-relief medication |
| simvastatin | FLOLIPID, ZOCOR | Cholesterol-lowering statin |
| sucralfate* | CARAFATE | Duodenal ulcer drug |
†Brand-name combination products that contain other active ingredients are not listed.
*Designated as Limited Use by Worst Pills, Best Pills News
**Designated as Do Not Use by Worst Pills, Best Pills News
***Designated as Do Not Use for Osteoporosis by Worst Pills, Best Pills News
Drugs whose own effects are impacted by levothyroxine
Levothyroxine impairs the effects of certain medications when they are taken concomitantly with it. For example, it reduces the therapeutic effects of the heart medication digoxin (LANOXIN) and the diabetes drug insulin (HUMALOG, HUMULIN, LANTUS, LEVEMIR, NOVOLIN, NOVOLOG and others).[7]
In contrast, levothyroxine increases the effects of the alpha-adrenergic agonist midodrine (ORVATEN), resulting in an increased risk of hypertension, and certain blood thinners such as warfarin (JANTOVEN), resulting in an increased risk of bleeding.[8]
In addition, concomitant use of levothyroxine and tricyclic antidepressants (such as amitriptyline [generic only]) or tetracyclic antidepressants (such as maprotiline [generic only]) may increase the therapeutic and toxic effects of both drugs.
Levothyroxine food interactions
Concurrent consumption of certain foods and drinks with levothyroxine may decrease or delay its absorption. These include fiber products (such as bran flakes, fiber bars, and whole-wheat or fiber drinks), coffee, cottonseed meal, grapefruit, soybean products (which may be present in some flours and infant formulas) and walnuts.[9],[10]
In addition, concomitant use of levothyroxine with kelp may result in increased risk of either hypothyroidism or hyperthyroidism (overactive thyroid), altered levothyroxine dosage requirements or inaccurate thyroid function tests.[11]
What You Can Do
If you need treatment with levothyroxine, take it on an empty stomach, ideally one-half to one hour before breakfast with water, not juice, coffee or — in the case of infants — soybean-based formula. Take levothyroxine at least an hour before consuming any of the interacting foods and drinks discussed in this article.
Review all your other medications with your doctor to assess for potentially significant drug interactions with levothyroxine. If any of your medications may interact with levothyroxine, your doctor may recommend that you take levothyroxine at least four hours before taking that medication. Your doctor also may adjust your levothyroxine dose, monitor your thyroid parameters more frequently or advise you to take an alternative medication instead of the interacting drug. Note that other oral drugs and certain injectable ones not mentioned in this article also may interact with levothyroxine. Never stop taking levothyroxine, skip a dose or take a higher or lower dose without medical supervision.
References
[1] AbbVie Inc. Label: levothyroxine (SYNTHROID). August 2022. https://www.accessdata.fda.gov/drugsatfda_docs/label/2022/021402Orig1s036Correctedlbl.pdf. Accessed January 9, 2023.
[2] IBM Micromedex. Drug interactions. http://www.micromedexsolutions.com/home/dispatch. Search term: “levothyroxine.” Accessed January 9, 2023.
[3] Balapatabendi M, Harris D, Shenoy SD. Drug interaction of levothyroxine with infant colic drops. Arch Dis Child. 2011;96(9):888-889.
[4] Skelin M, Lucijanić T, Amidžić Klarić D, et al. Factors affecting gastrointestinal absorption of levothyroxine: A review. Clin Ther. 2017;39(2):378-403.
[5] IBM Micromedex. Drug interactions. http://www.micromedexsolutions.com/home/dispatch. Search term: “levothyroxine.” Accessed January 10, 2023.
[6] AbbVie Inc. Label: levothyroxine (SYNTHROID). August 2022. https://www.accessdata.fda.gov/drugsatfda_docs/label/2022/021402Orig1s036Correctedlbl.pdf. Accessed January 10, 2023.
[7] AbbVie Inc. Label: levothyroxine (SYNTHROID). August 2022. https://www.accessdata.fda.gov/drugsatfda_docs/label/2022/021402Orig1s036Correctedlbl.pdf. Accessed January 10, 2023.
[8] IBM Micromedex. Drug interactions. http://www.micromedexsolutions.com/home/dispatch. Search term: “levothyroxine.” Accessed January 10, 2023.
[9] AbbVie Inc. Label: levothyroxine (SYNTHROID). August 2022. https://www.accessdata.fda.gov/drugsatfda_docs/label/2022/021402Orig1s036Correctedlbl.pdf. Accessed January 10, 2023.
[10] Wiesner A, Gajewska D, Paśko P. Levothyroxine interactions with food and dietary supplements–A systematic review. Pharmaceuticals (Basel). 2021;14(3):206.
[11] IBM Micromedex. Drug interactions. http://www.micromedexsolutions.com/home/dispatch. Search term: “levothyroxine.” Accessed January 10, 2023.
