Is Zinc Safe with Synthroid?
Free · No account · based on published sources including NIH ODS, FDA drug labels, and peer-reviewed literature
Take Synthroid at least 2–4 hours apart from zinc supplements. Take Synthroid first thing in the morning on an empty stomach, and separate zinc supplements until midday or evening. Monitor TSH if zinc supplementation is started or stopped.
Why this interaction occurs
Zinc can chelate with levothyroxine (Synthroid) in the gastrointestinal tract, potentially reducing its absorption. Additionally, zinc is a necessary cofactor for thyroid hormone receptor binding and peripheral T4 to T3 conversion. While zinc deficiency impairs thyroid function, high-dose zinc supplements taken simultaneously with Synthroid may competitively bind the drug and reduce its bioavailability.
Evidence
Evidence level: limited.
Reported safety data
The FDA’s adverse event reporting system (FAERS) has received 185,542 reports mentioning Synthroid. This reflects reported cases involving the medication in general — not confirmed causation, and not specific to the Synthroid + 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 Zinc interactions → · All Synthroid interactions →
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Educational only — not medical advice.
Always confirm with your doctor or pharmacist.