hypothyroidism
11 interactions related to hypothyroidism
levothyroxine + iron
When taken at the same time, iron can reduce how much levothyroxine your body absorbs by forming a poorly soluble complex in the gut, which can blunt the effect of your thyroid medication and raise TSH.
levothyroxine + calcium
Calcium can reduce levothyroxine absorption when the two are taken close together
levothyroxine + biotin
Biotin (vitamin B7) does not interact with levothyroxine pharmacologically and does not change how the medication is absorbed or works. The issue is in the lab: high-dose biotin can interfere with the biotin-streptavidin immunoassays used to measure TSH, free T4, free T3, and thyroglobulin, which can produce a falsely low TSH and falsely high T4/T3 pattern that mimics an overactive thyroid and can prompt an inappropriate dose change.
levothyroxine + soy
Soy protein and isoflavones can bind to levothyroxine in the gut and reduce how much of the dose is absorbed, which can raise TSH and, in some people, increase the dose needed to stay in range. The effect is most relevant with large, variable soy intake taken close to the dose, and is best documented in infants fed soy formula.
cabbage + levothyroxine
Cabbage and other brassica vegetables release thiocyanates and goitrin that can compete with iodide uptake at the thyroid and interfere with hormone synthesis. In normal, mostly-cooked portions this has no meaningful effect on levothyroxine in iodine-sufficient adults. Concern is limited to very large, sustained raw-cruciferous intakes or iodine-poor diets.
levothyroxine + fiber
Dietary and supplemental fiber can bind levothyroxine in the gut and modestly reduce how much of each dose is absorbed. When fiber intake is high or variable around the time of dosing, this can nudge TSH upward and make a stable dose harder to settle on. The effect is real but generally modest, and it is managed mainly by timing and consistency rather than by avoiding fiber.
tempeh + levothyroxine
Tempeh is a fermented soybean cake rich in soy protein, and soy protein binds levothyroxine in the gut and reduces how much of the thyroid hormone is absorbed. Fermentation lowers isoflavone bioavailability but leaves the soy protein intact, so the absorption interference remains. Taken consistently close to the dose, this can lower thyroid hormone levels enough to push TSH out of its target range.
levothyroxine + coffee
Coffee can reduce how much levothyroxine you absorb when the two are taken at the same time. Chlorogenic acids and other compounds in coffee appear to bind the hormone in the gut, and coffee can also speed gastric transit, leaving less time for the tablet to dissolve. The effect largely disappears when the dose and the coffee are separated by enough time.
edamame + levothyroxine
Edamame is whole young soybeans. Soy protein and isoflavones can bind levothyroxine in the gut and modestly reduce how much is absorbed if the two are taken close together. The evidence is limited and mixed: case reports and one pharmacokinetic study suggest a small reduction in absorption, while the only randomized crossover study found no significant effect. Any impact is best avoided simply by separating the dose from soy-rich meals.
cauliflower + levothyroxine
Cauliflower is a cruciferous vegetable whose breakdown products (thiocyanates) can theoretically compete with iodine uptake by the thyroid. In practice, a 2024 systematic review found brassica vegetables at normal dietary intakes do not impair thyroid function when iodine is adequate, and because levothyroxine is hormone you swallow as a tablet, ordinary cauliflower portions do not meaningfully affect it.
tofu + levothyroxine
Tofu is one of the most concentrated sources of soy protein in the diet. Soy protein binds levothyroxine in the gut and reduces how much of the drug is absorbed, and case reports describe TSH rising when soy-heavy foods like tofu are added to a previously stable levothyroxine regimen. The effect is modest in most adults but clinically relevant in sensitive patients, and it is managed by timing.