FOLFIRI — What This Regimen Is and What to Expect
FOLFIRI is a three-drug chemotherapy combination used most commonly for colorectal cancer. If it has appeared on your treatment plan and nobody has expanded the acronym, this page does that — and explains which side effects are most important to prepare for.
- Three drugs — Folinic acid, fluorouracil and irinotecan make up FOLFIRI.
- Different from FOLFOX in one key drug — Irinotecan replaces oxaliplatin, which changes the side-effect profile entirely.
- Diarrhoea, not nerve tingling — The numbness and cold sensitivity linked to FOLFOX are not a feature of FOLFIRI. Diarrhoea is.
- Hair thinning is common — Irinotecan causes temporary hair loss in many people. It usually grows back after treatment ends.
Medically reviewed by Dr. Naresh Gundu, Medical Oncologist, MBBS (Chalmeda Anand Rao Institute of Medical Sciences, Karimnagar) · DNB Internal Medicine (Sir Gangaram Hospital, New Delhi) · DM Medical Oncology (AIIMS) · Last reviewed September 2026
FOLFIRI is a combination chemotherapy regimen made up of three medicines: folinic acid (leucovorin), fluorouracil (5-FU) and irinotecan. It is given by intravenous infusion and is used most commonly for colorectal cancer. The defining difference from FOLFOX is irinotecan in place of oxaliplatin — which means diarrhoea and hair thinning rather than nerve tingling.
What do the letters in FOLFIRI stand for?
Folinic acid — the FOL
Also called leucovorin. It is not a chemotherapy drug on its own. It is included because it makes the next drug, fluorouracil, work more effectively inside cancer cells.
Fluorouracil (5-FU) — the F
A chemotherapy drug that interferes with the way cancer cells copy their DNA, preventing them from multiplying. It is given as a rapid intravenous injection and then as a slower continuous infusion.
Irinotecan — the IRI
A chemotherapy drug that blocks an enzyme cancer cells need to unwind their DNA during replication. This is the drug that sets FOLFIRI apart from FOLFOX and is responsible for the diarrhoea and hair thinning most people on this regimen notice.
How is FOLFIRI different from FOLFOX?
Both regimens share folinic acid and fluorouracil. The only difference is the third drug: FOLFOX uses oxaliplatin, FOLFIRI uses irinotecan.
That one change alters the side-effect profile completely. Oxaliplatin is associated with peripheral neuropathy — numbness, tingling and cold sensitivity that can outlast treatment, sometimes permanently. Irinotecan does not cause neuropathy.
Instead, irinotecan brings diarrhoea and hair thinning. Those two differences are often central to the conversation when your oncologist is deciding which regimen suits your situation.
Who is FOLFIRI not suitable for?
FOLFIRI is not suitable for everyone. Eligibility is decided by an oncologist on the individual case, based on testing and your overall health.
It is not used, or used with caution, in the following situations:
- UGT1A1 gene variants: Some people carry a genetic change that slows how the body processes irinotecan. Without genetic testing, this can lead to severe side effects. Your oncologist may arrange a blood test before treatment starts.
- Severely reduced liver function: Irinotecan is broken down in the liver. Severe liver impairment changes how the drug behaves in the body.
- Active severe infection: Chemotherapy suppresses the immune system and is not started while a serious infection is untreated.
- Bone marrow already significantly suppressed: FOLFIRI reduces blood counts further. It is not given when counts are already too low to treat safely.
- Pregnancy: This regimen is not used during pregnancy.
Is the diarrhoea on FOLFIRI dangerous?
Diarrhoea from irinotecan comes in two distinct forms that are managed differently, so knowing which type you have matters.
Early-onset diarrhoea can happen during or shortly after the infusion. It is a cholinergic effect — a nerve-related response to the drug — and your clinical team is prepared for it. Tell the nurse if it starts while you are still in the infusion chair.
Delayed-onset diarrhoea starts later, often the day after the infusion or beyond, and this is the type that can become serious. It can lead to severe dehydration quickly. Contact your team the same day if it is significant, frequent or worsening — do not wait for your next scheduled appointment.
What other side effects does FOLFIRI cause?
Hair thinning or loss is common because of irinotecan. It is usually temporary — hair typically returns after treatment ends — but it can be distressing, and that is a reasonable response to have.
Low blood counts are expected during each cycle. Fatigue, a higher susceptibility to infection and bruising more easily are all related to this. Your team will check your counts before each infusion.
Nausea and mouth sores are associated with fluorouracil. Anti-nausea medicines are given as part of the regimen, and you will usually go home with medicine to continue. Tell your team if nausea is not being controlled — there are alternatives.
Words on the treatment sheet that need explaining
- FOLFIRI
- The name of the regimen, built from the first letters of its three drugs: folinic acid, fluorouracil and irinotecan.
- Irinotecan
- The IRI in FOLFIRI. A chemotherapy agent that blocks an enzyme cancer cells use to copy their DNA. The drug primarily responsible for diarrhoea and hair change in this regimen.
- Leucovorin (folinic acid)
- The FOL in FOLFIRI. Not a chemotherapy drug — a compound that makes fluorouracil more active inside tumour cells.
- 5-FU (fluorouracil)
- The F in FOLFIRI. A chemotherapy drug that disrupts DNA copying in cancer cells. Given as both a fast injection and a slower continuous infusion during the same visit.
- Nadir
- The lowest point of blood counts in a treatment cycle, typically reached in the days after the infusion ends. This is the period when infection risk is highest and when to monitor most carefully for fever.
- Cycle
- One complete course of FOLFIRI followed by a rest period before the next. FOLFIRI is given in multiple cycles; the planned number is set individually and discussed with you before treatment starts.
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Frequently asked questions
What does FOLFIRI stand for?
Each part of the acronym names one of the three drugs: FOL stands for folinic acid, F for fluorouracil and IRI for irinotecan. Knowing this matters because it tells you which drug is responsible for which side effects. Irinotecan — the IRI — is the drug most people notice first, through diarrhoea and, for many, temporary hair thinning. The other two drugs are shared with several related regimens.
How often is FOLFIRI given?
FOLFIRI is given in repeated cycles, with a rest period between each to allow your body to recover. The number of cycles planned is decided individually and will be discussed with you before treatment starts. Your oncologist will explain the schedule for your specific case and when blood tests are scheduled to monitor how your body is responding.
Will I lose all my hair on FOLFIRI?
Hair thinning or loss is common with FOLFIRI because of irinotecan. The extent varies between individuals — some experience significant loss, others notice thinning. It is usually temporary and hair typically grows back after treatment ends. It does not fall out all at once; if it happens, it usually begins some weeks into treatment. Ask your team whether a cold cap is appropriate for your situation.
What should I do if the diarrhoea is severe?
Contact your oncology team the same day — not at your next scheduled appointment. Severe diarrhoea can cause dehydration very quickly. If you cannot keep fluids down, or if there is blood in the stool, go to the emergency department rather than waiting for a callback. Your team will have given you guidance before treatment started about when to call; follow that guidance and err on the side of calling earlier rather than later.
Can I eat normally while on FOLFIRI?
Many people find appetite and food tolerance change during FOLFIRI cycles. Nausea, mouth sores and taste changes can all affect what you want to eat. Small, frequent meals often suit better than larger ones. If diarrhoea is active, your team will advise which foods to avoid temporarily. Do not restrict eating severely without guidance — the body needs nutrition to recover between cycles. Tell your team if eating has become very difficult.
Is FOLFIRI better than FOLFOX?
They are not directly comparable in the way that question implies. Both regimens share two of their three drugs and are used for some of the same cancers, but the choice between them is about matching the side-effect profile to your individual situation, health and preferences — not selecting the stronger one. FOLFOX neuropathy can persist after treatment ends, sometimes permanently, whereas FOLFIRI diarrhoea does not follow that long-term pattern. Your oncologist will explain why one was recommended for you specifically.
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