Hydrochlorothiazide and Fluorouracil Topical: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Hydrochlorothiazide
Fluorouracil Topical
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
Myelosuppression (granulocytopenia)
Interaction Deep Dive
Thiazide diuretics may enhance the myelosuppressive effects of antineoplastic agents. Fourteen breast cancer patients treated with a cyclophosphamide, methotrexate, 5-fluorouracil combination and a thiazide diuretic experienced significantly higher levels of granulocytes during treatment cycles without the thiazides as compared with cycles that included thiazides1.
Why it happens (mechanism)
Unknown
Common questions
Can I take Hydrochlorothiazide and Fluorouracil Topical together?
Myelosuppression (granulocytopenia) Always confirm with your pharmacist or prescriber before making any change.
How serious is the Hydrochlorothiazide and Fluorouracil Topical interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Hydrochlorothiazide or Fluorouracil Topical 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 (1)
- Orr LE: Potentiation of myelosuppression from cancer chemotherapy and thiazide diuretics. Drug Intell Clin Pharm 1981; 15:967-970. PubMed
Keep reading about Hydrochlorothiazide
Keep reading about Fluorouracil Topical
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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