Thiamine and Capecitabine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Capecitabine
Thiamine
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
Reduced thiamine exposure
Interaction Deep Dive
The thiamine pyrophosphate (TPP) effect of red cell transketolase activity, a measure of thiamine deficiency, was significantly elevated with adjuvant 5-fluorouracil chemotherapy in both new and treatment-experienced cancer patients in prospective studies. Thiamine deficiency occurred within 1 month of initiation of 5-fluorouracil alone or with combination therapy in treatment-naive patients. The deficiency was reversed within 12 weeks with thiamine 100 mg/day supplementation. Consider high-dose thiamine supplementation during 5-fluorouracil treatment1.
Why it happens (mechanism)
Unknown
Literature reports
1 report — tap to read
a) In a prospective study in treatment-naive cancer patients (mean age, 46.7 years) receiving 1-month of adjuvant chemotherapy regimens containing 5-fluorouracil (n=9), the thiamine pyrophosphate (TPP) effect of red cell transketolase activity, a measure of thiamine deficiency, rose significantly from 8.5% at baseline to 31.4%. TTP values in these patients reversed to 10.5% after 4 to 12 weeks of thiamine 100 mg/day supplementation. In another prospective study, adjuvant treatment with non 5-fluorouracil chemotherapy drugs in treatment-experienced patients (n=10; mean age, 61.6) had no significant effect on TPP values (TPP, 11%) when compared with age-matched healthy controls (n=10; TPP, 7.8%). Patients treated with 5-fluorouracil-based regimens (n=26), however, experienced significant TPP elevations (TPP, 20.2%) 1.
Common questions
Can I take Thiamine and Capecitabine together?
Reduced thiamine exposure Always confirm with your pharmacist or prescriber before making any change.
How serious is the Thiamine and Capecitabine interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How strong is the evidence for this interaction?
The evidence is graded "established". Well documented — supported by controlled studies or strong clinical data.
Questions for your pharmacist
- Does my dose of Thiamine or Capecitabine 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)
- Aksoy M, Basu TK, Brient J, et al: Thiamin status of patients treated with drug combinations containing 5-fluorouracil. Eur J Cancer 1980; 16(8):1041-1045. PubMed
Keep reading about Capecitabine
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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