Medication·Interactions·Reviewed June 9, 2026
Levothyroxine interactions.
Levothyroxine has 20 documented interactions in the NutriStack database. The full interaction list is below. None of this is a substitute for your prescriber's advice.
Levothyroxine at a glance.
A quick, data-grounded summary. The full tables are below.
Levothyroxine has 20 documented interactions in the NutriStack database. The full interaction list is below. None of this is a substitute for your prescriber's advice.
Substances that interact with levothyroxine.
Every supplement and medication in the NutriStack database with a documented interaction with this drug, highest-severity first. Open any pair for the mechanism and sources.
| Substance | Interaction | What happens |
|---|---|---|
| Ashwagandha | Caution | Ashwagandha has been associated with increased thyroid hormone levels and rare thyrotoxicosis reports. When combined with levothyroxine, it may... |
| Biotin | Caution | Biotin (vitamin B7) does not pharmacologically interact with levothyroxine, but it causes clinically dangerous interference with thyroid laboratory... details → |
| DIM | Caution | DIM (diindolylmethane) may affect thyroid hormone metabolism by inducing phase II conjugation enzymes. It can alter the estrogen-thyroid axis... |
| Vitamin B7 | Caution | High-dose biotin (>5mg/day) interferes with streptavidin-biotin immunoassays used to measure TSH and free T4. This creates FALSELY NORMAL OR... details → |
| Calcium | Timing Sensitive | Calcium supplements significantly reduce levothyroxine absorption by 20-25% through chelation in the gastrointestinal tract. This can lead to... details → |
| Chromium | Timing Sensitive | Chromium supplements, particularly chromium picolinate, have been shown in a small human absorption study to reduce levothyroxine exposure. This can... details → |
| Coenzyme Q10 Ubiquinol | Timing Sensitive | CoQ10 may have a minor effect on levothyroxine absorption if taken concurrently. While the interaction is not well-studied, the general... |
| Coffee | Timing Sensitive | Coffee significantly reduces levothyroxine absorption when consumed within 60 minutes of taking the medication. Chlorogenic acids and tannins in... details → |
| Iron | Timing Sensitive | Iron supplements form an insoluble complex with levothyroxine in the GI tract, reducing thyroid hormone absorption by up to 75% in some studies.... details → |
| Iron Bisglycinate | Timing Sensitive | Iron bisglycinate contains elemental iron and should be handled like other oral iron supplements around levothyroxine. Iron can bind thyroid hormone... details → |
| Magnesium Citrate | Timing Sensitive | Magnesium-containing products can interfere with levothyroxine absorption when taken together. The best evidence is for magnesium antacids and other... |
| Magnesium Glycinate | Timing Sensitive | Magnesium supplements, particularly magnesium oxide and magnesium hydroxide (antacid forms), can reduce levothyroxine absorption by forming chelate... details → |
| Magnesium L-Threonate | Timing Sensitive | Magnesium L-threonate has not been studied directly with levothyroxine, but it supplies magnesium ions that may interfere with thyroid hormone... |
| Magnesium Malate | Timing Sensitive | Magnesium malate may reduce levothyroxine absorption if taken at the same time. Direct studies with this exact magnesium salt are lacking, but the... |
| Magnesium Taurate | Timing Sensitive | Magnesium taurate may interfere with levothyroxine absorption when taken together. This is an extrapolation from magnesium-containing products and... |
| Psyllium Husk | Timing Sensitive | Fiber supplements, particularly psyllium, can bind levothyroxine in the gastrointestinal tract and reduce its absorption. Studies have shown that... details → |
| Soy Isoflavones | Timing Sensitive | Soy isoflavones (genistein and daidzein) can reduce levothyroxine absorption by binding to the medication in the gastrointestinal tract, forming... details → |
| Zinc | Timing Sensitive | Zinc supplements may reduce levothyroxine absorption through chelation in the gastrointestinal tract. While the evidence is less robust than for... |
| Zinc Carnosine | Timing Sensitive | Zinc carnosine supplies zinc, a divalent mineral that may interfere with levothyroxine absorption if taken at the same time. Direct... |
| Zinc Picolinate | Timing Sensitive | Zinc picolinate may interfere with levothyroxine absorption if taken together. The evidence is weaker than for calcium or iron, but levothyroxine is... |
The full levothyroxine profile.
Uses, typical dosing, side effects, and the cited evidence for this medication.
Common levothyroxine questions.
Quick answers drawn from the tables above.
What interacts with Levothyroxine?
In the NutriStack database, Levothyroxine has 20 documented interactions. The most notable include Ashwagandha, Biotin, DIM, Vitamin B7, and Calcium. Check any specific combination before taking it and confirm with your prescriber.
Is it safe to take Ashwagandha with Levothyroxine?
NutriStack classifies the Ashwagandha and Levothyroxine pairing as caution: Ashwagandha has been associated with increased thyroid hormone levels and rare thyrotoxicosis reports. When combined with levothyroxine, it may contribute to... Avoid starting ashwagandha on your own if you take levothyroxine for thyroid replacement or TSH suppression. If you use it, tell your prescriber and... Always confirm with your prescriber.
Check your whole stack
See how levothyroxine fits your supplements.
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