Levamisole and Fluorouracil: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Fluorouracil
Levamisole
No brand names on record
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
Hepatotoxicity
Interaction Deep Dive
A prospective, randomized study of 1,025 colon cancer resection patients who received either no treatment, levamisole monotherapy, or treatment with fluorouracil plus levamisole demonstrated a significantly higher rate of hepatotoxicity with the combination (39.6%) than with levamisole alone (16.3%) or no treatment (16.1%)1. Hepatotoxicity was described as reversible and characteristically mild and asymptomatic, most commonly taking the form of an elevated alkaline phosphatase, often accompanied by increased transaminases or serum bilirubin.
Why it happens (mechanism)
Additive hepatotoxic effects
Common questions
Can I take Levamisole and Fluorouracil together?
Hepatotoxicity Always confirm with your pharmacist or prescriber before making any change.
How serious is the Levamisole and Fluorouracil 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 "probable". Good supporting evidence, though not definitively proven.
Questions for your pharmacist
- Does my dose of Levamisole or Fluorouracil 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)
- Moertel CG, Fleming TR, MacDonald JS, et al: Hepatic toxicity associated with fluorouracil plus levamisole adjuvant therapy. J Clin Oncol 1993; 11:2386-2390. DOI
Keep reading about Fluorouracil
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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