Can I Take These?

Can You Take Aspirin and Levothyroxine Together?

Levothyroxine's FDA label describes an effect of high-dose salicylates on thyroid hormone lab measurements, at doses well above typical aspirin use.

MonitorEvidence: Moderate

See the full Aspirin page and Levothyroxine page for other reviewed interactions and reference information.

What the interaction means

Levothyroxine's FDA prescribing information includes "Salicylates (> 2 g/day)" in "Table 3: Drugs That May Alter T4 and Triiodothyronine (T3) Serum Transport," stating: "Salicylates inhibit binding of T4 and T3 to TBG and transthyretin. An initial increase in serum FT4 is followed by return of FT4 to normal levels with sustained therapeutic serum salicylate concentrations, although total T4 levels may decrease by as much as 30%." Aspirin's own label does not mention thyroid hormone or levothyroxine.

Why it may happen

High-dose salicylates compete with thyroid hormone for binding to serum transport proteins (thyroxine-binding globulin and transthyretin), which can transiently alter measured free and total thyroid hormone levels.

Practical context

This entry specifically concerns salicylate doses above 2 g/day, well above typical low-dose (81-325 mg/day) cardioprotective or occasional pain-relief aspirin use, and describes changes in lab measurements rather than a described clinical bleeding or efficacy risk. It is most relevant to chronic, high-dose aspirin or salicylate therapy; anyone on levothyroxine starting or stopping high-dose aspirin therapy should mention it to the prescriber monitoring thyroid function tests.

What the sources say

DURLAZA (Aspirin) Extended-Release Capsules — FDA Prescribing Information — New Haven Pharmaceuticals, Inc. (via DailyMed, U.S. National Library of Medicine)Levothyroxine Sodium Capsules — FDA Prescribing Information — YARAL Pharma, Inc. (via DailyMed, U.S. National Library of Medicine)

Last reviewed 2026-08-24

Medical information disclaimer: this information is general and educational. It does not diagnose conditions, prescribe treatment, or determine whether a combination is safe for you personally. Follow your prescription label and ask a pharmacist or clinician before starting, stopping, or combining products. Full disclaimer.

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