Levothyroxine is a synthetic thyroid hormone used to treat hypothyroidism, a condition where the thyroid gland doesn't produce enough hormones [1.2.5]. For this medication to be effective, it must be absorbed properly in the small intestine [1.2.5]. However, numerous substances can interfere with this process. Taking levothyroxine on an empty stomach, typically 30 to 60 minutes before breakfast with only water, is the standard recommendation to maximize absorption [1.2.2, 1.2.9].
Medications That Interfere with Levothyroxine
Several over-the-counter (OTC) and prescription drugs can reduce levothyroxine's effectiveness, primarily by decreasing its absorption from the gut [1.3.2, 1.3.4]. In most cases, a 4-hour gap between taking levothyroxine and these medications is recommended to prevent interactions [1.3.4, 1.5.1].
Acid Reducers and Antacids
Medications that reduce stomach acid, such as proton pump inhibitors (PPIs) and antacids, can significantly impair levothyroxine absorption [1.2.4, 1.3.5]. Levothyroxine requires an acidic environment to be absorbed properly [1.2.4].
- Proton Pump Inhibitors (PPIs): Examples include omeprazole (Prilosec), esomeprazole (Nexium), and lansoprazole (Prevacid) [1.3.5, 1.3.7]. Since their effect is long-lasting, simply spacing the doses may not be enough, and a dose adjustment of levothyroxine might be necessary [1.2.6].
- Antacids: Products containing aluminum, magnesium, or calcium carbonate (like Tums, Maalox, Rolaids) can bind to levothyroxine and prevent its absorption [1.2.4, 1.3.5]. These should be taken at least 4 hours apart from your thyroid medication [1.5.3].
Cholesterol-Lowering Drugs
Certain medications used to lower cholesterol, known as bile acid sequestrants, can bind to levothyroxine in the intestine.
- Examples: Cholestyramine (Prevalite), colestipol (Colestid), and colesevelam (Welchol) [1.3.1, 1.3.5].
- Recommendation: Take levothyroxine at least 4 hours before these medications to avoid the interaction [1.3.1, 1.4.3].
Other Prescription Medications
- Sucralfate (Carafate): Used for treating ulcers, this medication can also bind to levothyroxine and should be separated by at least 4 hours [1.4.3, 1.5.9].
- Phosphate Binders: Drugs like sevelamer (Renvela) and lanthanum carbonate, used in patients with kidney disease, are known to interfere with absorption [1.2.4, 1.3.2].
- Certain Antibiotics: Rifampin can accelerate the metabolism of levothyroxine, potentially requiring a higher dose [1.3.1]. Ciprofloxacin can decrease its absorption [1.3.6, 1.3.8].
- Estrogens: Found in birth control pills and hormone replacement therapy (HRT), estrogens can increase the amount of thyroid-binding globulin, which may necessitate a levothyroxine dose adjustment [1.2.4, 1.3.1].
Supplements and Minerals to Avoid
Many common dietary supplements can bind to levothyroxine, preventing your body from getting the full dose. The general rule is to wait at least 4 hours after taking levothyroxine before taking these supplements [1.5.7].
- Iron: Ferrous sulfate, a common iron supplement, forms an insoluble complex with levothyroxine [1.3.2]. This includes multivitamins that contain iron [1.4.8].
- Calcium: Calcium supplements, including calcium carbonate and calcium citrate, significantly reduce levothyroxine absorption [1.3.2, 1.4.9].
- Magnesium and Aluminum: These minerals, often found in antacids and other supplements, also interfere with absorption [1.2.6, 1.4.6].
- Biotin (Vitamin B7): Biotin doesn't interfere with levothyroxine absorption but can cause incorrect thyroid function test results [1.4.5, 1.4.6]. It's recommended to stop taking biotin for at least two days before having thyroid labs drawn [1.4.5].
Foods and Beverages That Cause Interactions
Consistency is key when taking levothyroxine. Certain foods and drinks can also inhibit its absorption. It's best to wait at least 30-60 minutes after your dose before eating or drinking anything other than water [1.2.1, 1.2.5].
- Coffee and Tea: Caffeinated beverages like coffee and tea are well-documented to reduce the absorption of levothyroxine [1.2.1, 1.6.3]. You should wait at least 30-60 minutes after your medication before drinking them [1.2.1].
- Soy Products: Soy, found in foods like tofu, soy milk, and edamame, can interfere with absorption [1.2.1, 1.2.5]. A four-hour gap between levothyroxine and soy consumption is often advised [1.4.5, 1.4.8].
- High-Fiber Foods: Foods high in dietary fiber, such as whole grains, legumes, and certain fruits and vegetables, can bind to the medication and reduce its bioavailability [1.2.3, 1.2.5].
- Calcium-Rich Foods: Dairy products like milk, cheese, and yogurt can interfere similarly to calcium supplements. A 4-hour waiting period is recommended [1.2.1, 1.2.5].
- Grapefruit Juice: Grapefruit juice can delay and reduce the absorption of levothyroxine and is best avoided around the time of your dose [1.2.3, 1.6.4].
- Walnuts and Cottonseed Meal: These are also known to decrease the absorption of levothyroxine [1.2.4, 1.2.5].
| Substance | Type | Recommended Waiting Time | Mechanism of Interaction |
|---|---|---|---|
| Calcium Supplements | Mineral/Supplement | At least 4 hours [1.3.4] | Binds to levothyroxine, reducing absorption [1.3.2]. |
| Iron Supplements | Mineral/Supplement | At least 4 hours [1.5.3] | Binds to levothyroxine, reducing absorption [1.3.2]. |
| Antacids (Tums, Maalox) | Medication (OTC) | At least 4 hours [1.5.3] | Reduces stomach acidity and binds to the drug [1.2.4]. |
| Proton Pump Inhibitors (PPIs) | Medication (Prescription/OTC) | Discuss with doctor; spacing may not be enough [1.2.6] | Reduces stomach acid needed for absorption [1.2.4]. |
| Coffee/Tea | Beverage | 30-60 minutes [1.2.1] | Reduces absorption [1.6.3]. |
| Soy Products | Food | At least 4 hours [1.4.8] | Interferes with absorption [1.2.5]. |
| High-Fiber Foods | Food | 30-60 minutes [1.2.5] | Binds to levothyroxine in the gut [1.2.5]. |
| Grapefruit Juice | Beverage | Avoid around dosing time [1.6.2, 1.6.4] | Delays and reduces absorption [1.6.4]. |
Conclusion
To ensure the effectiveness of levothyroxine therapy, it is vital to be aware of what cannot be taken with it. The cornerstone of proper administration is taking the medication on an empty stomach with water and waiting 30-60 minutes before consuming food or other beverages [1.2.9]. For interacting medications and supplements, particularly those containing calcium, iron, or aluminum, a 4-hour separation is crucial [1.5.1]. Always maintain open communication with your healthcare provider about all medications, supplements, and significant dietary changes to ensure your thyroid hormone levels remain stable and within the target range. Consistency in how and when you take your medication is paramount for successful treatment of hypothyroidism [1.5.3].
An authoritative outbound link to the NHS page on Levothyroxine
