Raw research findings for this medication. Mostly single studies, not curated or confirmed robust.
Fluorouracil (5-FU) is one of the most widely used chemotherapy medicines, an antimetabolite that stands in for a DNA and RNA building block and blocks thymidylate synthase, so cancer cells cannot make DNA. It is given by drip for bowel, stomach, pancreatic, breast and head and neck cancers, usually in combinations such as FOLFOX and FOLFIRI, and as a cream for skin lesions. It is sold as Adrucil, among other names.
DPYD makes dihydropyrimidine dehydrogenase, the enzyme that breaks down more than 80 percent of fluorouracil. A few DPYD variants (among them *2A, rs3918290, and c.2846A>T, rs67376798) make less working enzyme; people who carry one keep far more of the drug active, with a much higher chance of severe side effects. About 3 to 8 in 100 people of European ancestry carry one. CPIC and DPWG have published guidelines on DPYD and fluorouracil, and the US and EU labels discuss it. Other genes such as TYMS have been studied, with weaker evidence.
Clinical guidelines that name a gene for Fluorouracil. They sort people into groups by the gene copies they carry.
CPIC guideline: DPYD. DPYD activity score 0 to 2. Strong. 2018.
DPWG guideline: DPYD. DPYD activity score 0 to 2. 2020.
US FDA: DPYD. DPYD activity score 0 to 0.5. 2024.
Every published finding on gene variants and Fluorouracil. Upload your DNA file to see which of these rows apply to you.
PharmGKB weighs all studies of a variant and rates how strong the evidence is, from 1A (strongest) to 4.
DPYD rs3918290: Level 1A · replicated. Toxicity: Neoplasms. 52.
DPYD rs67376798: Level 1A · replicated. Toxicity: Neoplasms. 23.
DPYD rs3918290: Level 1A · replicated. Other. 23.
DPYD rs2297595: Level 1A · replicated. Toxicity: Neoplasms. 17.
Studies of how quickly the body processes this medication.
Studies of how well it worked in people carrying a variant.
Studies of how much of the drug people needed or tolerated.
Studies of side effects in people carrying a variant.
Study findings and evidence levels: PharmGKB (CC BY-SA 4.0). Guidelines: CPIC and DPWG, as bundled in PharmCAT. Most studies were done mainly in people of European ancestry.
More drugs from the same category
Not a prescribing recommendation. This page is educational information about pharmacogenomic research and clinical guidelines - it is not medical or dosing advice, and not a prediction of how any medication will work for you. Never start, stop, or change a medication or dose based on it; talk to your doctor or pharmacist, who can order clinical-grade testing if appropriate.
Content updated September 2026.
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