What Medications Should I Avoid Taking with Levothyroxine?

October 12, 2025 •

4 min read

Drug interactions can reduce the effectiveness of levothyroxine by up to 25%, according to a study on coadministered calcium preparations. For individuals treating hypothyroidism, knowing what medications should be avoided or carefully timed with levothyroxine is critical for managing thyroid hormone levels and preventing complications.

Quick Summary

This guide details the major categories of drugs and supplements that can interfere with levothyroxine absorption or alter its effectiveness, including spacing recommendations and considerations for certain formulations. It provides a table of common interactions and offers advice for minimizing risks.

Key Points

Medication Spacing: Always take levothyroxine on an empty stomach, at least 30-60 minutes before food and at least four hours away from interacting medications and supplements.
Common Interferences: Antacids, calcium, and iron supplements are common culprits that bind to levothyroxine and reduce its absorption.
Dietary Factors: Soy products, coffee, grapefruit juice, and high-fiber foods can interfere with absorption and should be spaced from your dose.
Hidden Interactions: Some multivitamins contain iron and calcium, creating an interaction. Always check the ingredients and separate timing by at least four hours.
Proton Pump Inhibitors: These medications can reduce gastric acidity, hindering tablet dissolution. Liquid formulations may be a better alternative for some patients.
Close Monitoring: Medications like estrogens, some seizure drugs, and certain antidepressants can affect thyroid levels and may require more frequent TSH level monitoring.
Consistency is Key: When concurrent medication is unavoidable, maintaining consistent timing and monitoring is crucial to allow for proper dose adjustments.

Navigating Drug Interactions with Levothyroxine

Levothyroxine is a narrow therapeutic index drug, meaning small changes in absorption can significantly impact thyroid hormone levels and overall health. Many common medications, supplements, and even foods can bind to levothyroxine, hindering its absorption in the gut and reducing its effectiveness. To ensure proper treatment, it is crucial to understand these interactions and manage your medication timing carefully.

Key Classes of Medications to Space Out

A wide range of drugs can interfere with the absorption of levothyroxine, and the most common strategy to manage this is to separate the dosing times. For many of these medications, a separation of at least four hours is recommended. This is because the binding often occurs in the gastrointestinal tract, and adequate time is needed for the levothyroxine to be absorbed on its own.

Antacids and Acid Reducers

Antacids that contain aluminum, magnesium, or calcium can bind to levothyroxine, preventing it from being fully absorbed. This includes products like Maalox, Tums, and Milk of Magnesia. Similarly, proton pump inhibitors (PPIs) such as omeprazole (Prilosec) and lansoprazole (Prevacid), which decrease gastric acid, can also impair levothyroxine tablet absorption. Gastric acidity aids in the dissolution of levothyroxine tablets, so reducing it can make the medication less effective.

Calcium and Iron Supplements

Both calcium supplements (including calcium carbonate) and iron supplements (ferrous sulfate) are notorious for decreasing levothyroxine's absorption. This interaction is also seen in multivitamins that contain these minerals. Studies have shown that concurrent administration of iron can significantly raise TSH levels, indicating reduced effectiveness of levothyroxine. Patients should separate their levothyroxine dose from these supplements by at least four hours.

Bile Acid Sequestrants

These medications, used to lower cholesterol, can bind to levothyroxine in the digestive tract. Examples include cholestyramine (Prevalite), colesevelam (Welchol), and colestipol (Colestid). Bile acid sequestrants should be administered at least 4 hours after levothyroxine to minimize binding.

Other Absorptive Inhibitors

Other drugs that can interfere with absorption include phosphate binders (like sevelamer and lanthanum), ulcer medications (sucralfate), and the weight-loss drug orlistat. The binding mechanism is similar to that of antacids and supplements, emphasizing the need for proper spacing. Sodium polystyrene sulfonate (Kayexalate), used to treat high potassium levels, is another medication that requires a separation of at least 4 hours.

Medications Requiring TSH Monitoring

Beyond absorption issues, some medications can affect your body's overall thyroid hormone levels or metabolism by other mechanisms. These may not require strict timing separation but necessitate more frequent monitoring of TSH levels by your healthcare provider.\n\n Estrogens: Found in oral contraceptives and hormone replacement therapy, estrogens can increase the level of thyroid-binding globulin, requiring a higher dose of levothyroxine.\n Seizure medications: Phenytoin and carbamazepine can accelerate the breakdown of thyroid hormones in the liver.\n Rifampin: This antibiotic can increase the metabolism of levothyroxine, leading to decreased hormone concentrations and potentially requiring a dosage increase.\n Certain Antidepressants: While the interaction is less severe, some antidepressants like amitriptyline and fluoxetine can impact thyroid levels.\n Statins: Some studies have observed an interaction between statins and levothyroxine, with patients potentially needing closer monitoring of their thyroid function.\n Amphetamines: Taking large doses of levothyroxine with amphetamines (e.g., Adderall, Desoxyn) can cause serious or life-threatening problems. This combination can increase the risk of adverse effects on the heart.

Foods and Beverages that Affect Absorption

It's not just medications; certain dietary choices can also impact levothyroxine effectiveness. Taking the medication on an empty stomach is key. Experts recommend taking levothyroxine at least 30 to 60 minutes before breakfast.

Soy Products: Compounds in soy (e.g., soy milk, tofu) can inhibit levothyroxine absorption. For infants, using non-soy formula is advised.\n Coffee: Studies suggest coffee can significantly reduce absorption. It's recommended to wait at least an hour after taking levothyroxine before drinking coffee.\n Dietary Fiber and Walnuts: High-fiber diets and excessive consumption of walnuts can also interfere with absorption.\n* Grapefruit Juice: Consuming grapefruit juice around the time of your dose can also decrease absorption.

Comparison Table: Common Levothyroxine Interactions

When Interactions are Unavoidable

Sometimes, avoiding interacting medications is not possible. In these cases, consistent timing is crucial. Your doctor may need to adjust your levothyroxine dose based on regular monitoring of your TSH levels to ensure your thyroid function remains stable. For patients on PPIs or those with significant absorption issues, alternative formulations like liquid levothyroxine or soft gel capsules can offer more consistent absorption. A study on liquid levothyroxine noted its absorption is less affected by PPIs compared to tablets.

Conclusion

Managing levothyroxine effectively requires a careful approach to all other medications, supplements, and even dietary factors. The primary strategy is to take levothyroxine on an empty stomach and separate it by at least four hours from key interfering agents like antacids, calcium, and iron. It is also essential to inform your healthcare provider of all the medications and supplements you take so they can proactively manage potential interactions and ensure your thyroid hormone levels remain stable. Always follow your doctor's instructions for monitoring and dosage adjustments to optimize your treatment.

Frequently Asked Questions

No, many multivitamins contain iron and calcium, which can significantly reduce the absorption of levothyroxine. You should separate the dose of your multivitamin from your levothyroxine by at least four hours.

It is recommended to wait at least one hour after taking levothyroxine before drinking coffee. Studies have shown that coffee can interfere with the absorption of thyroid medication.

While an isolated instance is unlikely to cause serious harm, it is important to be consistent with timing to maintain stable thyroid hormone levels. Inform your doctor and ensure you maintain proper spacing moving forward. If this happens frequently, discuss your timing challenges with your healthcare provider.

Yes, taking levothyroxine at bedtime (at least 4 hours after your last meal) can be an effective alternative, especially if you have a morning routine with coffee or other interacting medications. The key is consistency and taking it on an empty stomach.

You should discuss this with your doctor. Options include taking the PPI and levothyroxine at least four hours apart or considering a liquid or soft gel capsule formulation of levothyroxine, which may be less affected by changes in stomach acidity.

Not all interactions are related to absorption. Some medications, like oral estrogens and certain seizure drugs, alter the body's metabolism of thyroid hormones, which may require a dose adjustment based on TSH monitoring rather than just spacing.

Yes, aside from supplements and medications, certain foods can also interfere. This includes soy products, walnuts, cottonseed meal, grapefruit, and high-fiber foods. It is best to take levothyroxine on an empty stomach and avoid consuming these foods too close to your dose.

Yes, switching between brands or generics can affect the medication's absorption and effectiveness. Consistent use of the same formulation is important to maintain stable thyroid hormone levels.