Levothyroxine and Ciprofloxacin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Ciprofloxacin
No brand names on recordLevothyroxine
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Decreased efficacy of levothyroxine
Interaction Deep Dive
Ciprofloxacin can interfere with absorption of levothyroxine3. In a double-blind, randomized, crossover study (n=8), thyroxine AUC was decreased by 39% with concurrent oral doses of ciprofloxacin and levothyroxine 4. Additionally, TSH levels were increased in 2 patients on stable levothyroxine therapy after multi-week administration of oral ciprofloxacin 5. Avoid concomitant use if possible 1. If concomitant use is required, administer levothyroxine at least 4 hours before or after drugs that are known to interfere with absorption 2 and closely monitor thyroid status 4.
Why it happens (mechanism)
Interference with absorption of levothyroxine; possible competition for OATP1A2 receptors
Literature reports
2 reports — tap to read
a) During a prospective, double-blind, randomized study in healthy adult volunteers (n=8), mean baseline-corrected thyroxine (T4) AUC was significantly decreased by 39% with coadministration of ciprofloxacin and levothyroxine compared with crossover treatment with placebo and levothyroxine. Study doses were levothyroxine 1000 mcg orally and ciprofloxacin 750 mg orally. The washout period between study days was at least 4 weeks. Total plasma T4 concentrations were measured over a 6-hour period after dosing 4.
b) Two cases of unexplained hypothyroidism were reported in patients previously stable on levothyroxine who received oral ciprofloxacin for treatment of infection. In an 80-year-old woman with advanced thyroid cancer, thyroid stimulating hormone (TSH) was increased to 44 milli-international units/L following 4 weeks of ciprofloxacin 750 mg twice daily for treatment of osteomyelitis. Increase of her standard dose of levothyroxine 125 mcg/day to 200 mcg/day was ineffective, but thyroid function tests returned quickly to normal after discontinuation of ciprofloxacin. In a 79-year-old woman with a stable daily dose of levothyroxine 150 mcg, TSH increased from 1.6 to 19 milli-international units/L following 3 weeks of treatment with ciprofloxacin 500 mg twice daily for a wound infection. Thyroid function normalized in this patient with a switch from concomitant administration of the 2 drugs to a 6-hour separation 5.
Common questions
Can I take Levothyroxine and Ciprofloxacin together?
Decreased efficacy of levothyroxine Always confirm with your pharmacist or prescriber before making any change.
How serious is the Levothyroxine and Ciprofloxacin interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "rapid". Effects can appear quickly, often within about 24 hours of combining the drugs.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
- Can Ciprofloxacin INCREASE Appetite?
- Does Coconut Water Interact With Ciprofloxacin?
- Can You Take Cipro (Ciprofloxacin) With Alcohol?
- Black Currant Oil With Levothyroxine, Methotrexate, and a Statin
- Provitalize With Levothyroxine, Valacyclovir, and Citalopram
- Can Bovine Thyroid Replace Levothyroxine?
Questions for your pharmacist
- Does my dose of Levothyroxine or Ciprofloxacin need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there anything you'd monitor while I'm on both?
References (5)
- Centanni M, Duntas L, Feldt-Rasmussen U, et al: ETA guidelines for the use of levothyroxine sodium preparations in monotherapy to optimize the treatment of hypothyroidism. Eur Thyroid J 2025; 14(4):e250123. PubMed
- Product Information: TIROSINT oral capsules, levothyroxine sodium oral capsules. Akrimax Pharmaceuticals, LLC (per FDA), Cranford, NJ, 2012. DailyMed
- Garber JR, Cobin RH, Gharib H, et al: Clinical practice guidelines for hypothyroidism in adults: Co-sponsored by American Association of Clinical Endocrinologists and the American Thyroid Association. Endocr Pract 2012; 18(6):988-1028.
- Goldberg AS, Tirona RG, Asher LJ, et al: Ciprofloxacin and rifampin have opposite effects on levothyroxine absorption. Thyroid 2013; 23(11):1374-1378. PubMed
- Cooper JG, Harboe K, Frost SK, et al: Ciprofloxacin interacts with thyroid replacement therapy. BMJ 2005; 330(7498):1002. DOI
Keep reading about Ciprofloxacin
Keep reading about Levothyroxine
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