Is Soy Safe with Levothyroxine?
Free · No account · based on published sources including NIH ODS, FDA drug labels, and peer-reviewed literature
Avoid consuming soy-based supplements or large amounts of soy products within 3-4 hours of taking levothyroxine. Maintain consistent soy intake and inform your provider so dosage can be adjusted accordingly.
Why this interaction occurs
Soy isoflavones may inhibit the intestinal absorption of levothyroxine and may also interfere with thyroid hormone synthesis and peripheral conversion. Infants on soy formula have shown increased levothyroxine requirements.
Evidence
Evidence level: moderate.
Reported safety data
The FDA’s adverse event reporting system (FAERS) has received 302,514 reports mentioning Levothyroxine. This reflects reported cases involving the medication in general — not confirmed causation, and not specific to the Levothyroxine + supplement combination on this page.
FAERS reports are voluntary and cannot prove that a drug caused an event. Do not use report counts to assess the safety of this specific drug-supplement pair.
Frequently asked questions
Related interactions
All Soy interactions → · All Levothyroxine interactions →
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Educational only — not medical advice.
Always confirm with your doctor or pharmacist.