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Is Vitamin D Safe with Synthroid?

✓ LOW SEVERITY
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Synthroid Vitamin D
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Free · No account · based on published sources including NIH ODS, FDA drug labels, and peer-reviewed literature

WHAT YOU NEED TO KNOW

Maintain adequate vitamin D levels (target 40–60 ng/mL). Vitamin D3 supplements can be taken at any time and do not need to be separated from Synthroid by several hours. Annual or biannual vitamin D level testing is recommended in hypothyroid patients.

Why this interaction occurs

Vitamin D receptors are present in thyroid tissue, and vitamin D deficiency is highly prevalent in patients with autoimmune hypothyroidism (Hashimoto's). Low vitamin D is associated with higher thyroid peroxidase antibodies and poorer TSH control. While vitamin D does not directly block Synthroid absorption, deficiency may worsen autoimmune thyroid destruction and increase medication requirements. This is a clinically relevant supportive interaction.

Evidence

Evidence level: moderate.

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

Can I take Vitamin D with Synthroid?
Generally yes, with awareness that Maintain adequate vitamin D levels (target 40–60 ng/mL). Vitamin D3 supplements can be taken at any time and do not need to be separated from Synthroid by several hours. Annual or biannual vitamin D level testing is recommended in hypothyroid patients.
How long should I wait between Synthroid and Vitamin D?
Maintain adequate vitamin D levels (target 40–60 ng/mL). Vitamin D3 supplements can be taken at any time and do not need to be separated from Synthroid by several hours. Annual or biannual vitamin D level testing is recommended in hypothyroid patients.
Does Vitamin D affect how well Synthroid works?
Vitamin D receptors are present in thyroid tissue, and vitamin D deficiency is highly prevalent in patients with autoimmune hypothyroidism (Hashimoto's). Low vitamin D is associated with higher thyroid peroxidase antibodies and poorer TSH control. While vitamin D does not directly block Synthroid absorption, deficiency may worsen autoimmune thyroid destruction and increase medication requirements. This is a clinically relevant supportive interaction.

Related interactions

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All Vitamin D interactions →  ·  All Synthroid interactions →

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Educational only — not medical advice.
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