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5-Fluorouracil (5-FU, Fluracil): What to Expect from Treatment

Medically reviewed by Dr. Bharati Devi Gorantla, Medical Oncologist, MBBS · MD · DM (Adyar, Chennai) · ECMO · MRCP SCE (UK) · Last reviewed September 2026

5-Fluorouracil (5-FU) has been used in chemotherapy regimens for decades. Many regimens deliver it through a portable pump you carry home overnight — which surprises people who expect to leave the clinic without any equipment. The two side effects most worth knowing about before you start are mouth sores and hand-foot changes.

Medically reviewed by Dr. Bharati Devi Gorantla, Medical Oncologist, MBBS · MD · DM (Adyar, Chennai) · ECMO · MRCP SCE (UK) · Last reviewed September 2026

Prescription-only medicine.

5-Fluorouracil is a prescription-only medicine given under the supervision of a specialist oncologist in a hospital or licensed cancer centre. It cannot be started, stopped, or adjusted on the basis of anything you read online. It is not suitable for everyone — see who this is not for below.

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In short

5-Fluorouracil (5-FU, Fluracil) causes mouth sores, hand-foot changes, nausea, diarrhoea, and fatigue. Many people receive it through a portable pump they carry home overnight. Of all the side effects, mouth sores and changes to the palms and soles are the ones most worth knowing about before you start — both are manageable when you report them early.

In detail

What is 5-Fluorouracil and how does it work?

5-Fluorouracil — also known as 5-FU or by the Indian brand name Fluracil — is an antimetabolite chemotherapy that has been in clinical use for several decades. It works by interfering with the way cancer cells copy their DNA, which stops them dividing.

It is used across a range of cancers, including colorectal, gastric, oesophageal, breast, and head and neck cancers. Your oncologist will have chosen it based on your specific cancer type and treatment plan, usually as part of a combination regimen.

5-FU is a hospital-administered medicine. It is never self-administered and is not available outside a licensed treatment setting.

In detail

Why do some people go home with an infusion pump?

5-FU can be given as a short injection or as a continuous infusion over many hours. For a number of regimens — particularly in colorectal and gastric cancer — delivering it slowly over around 46 hours is built into how the regimen is designed.

The pump is a small, sealed device, sometimes called a balloon pump or elastomeric pump, which connects to your central line, PICC line, or port. You carry it home in a small shoulder bag and go about your day normally while it runs.

After around 46 hours you return to the clinic. The nurse disconnects the pump in a few minutes. Before you leave, your nurse will explain what to do if the pump leaks, sounds an alarm, or the line comes loose — the rule is always to call the clinic rather than trying to fix it yourself.

Checklist

What side effects does 5-FU cause?

Mouth sores (mucositis)Soreness, ulcers, or redness inside the mouth and throat, typically appearing a few days after treatment.
Hand-foot syndromeRedness, warmth, tenderness, and possible peeling of the palms and soles — report at the first sign of redness, before the skin breaks.
NauseaUsually managed with anti-sickness medicines your team prescribes before treatment begins.
DiarrhoeaLoose stools after treatment — tell your team if frequency increases or you cannot keep fluids down.
FatigueTiredness that can build across cycles; tell your team if it is affecting your daily life.
Lowered blood countsRaising your risk of infection, anaemia, and bruising — your blood is checked before each cycle to monitor this.

Eligibility

Who should not receive 5-Fluorouracil?

5-Fluorouracil is not given to everyone, and the decision depends on individual assessment by a specialist oncologist.

DPD enzyme deficiency: People who lack the enzyme dihydropyrimidine dehydrogenase (DPD) cannot break down 5-FU safely. Even a partial deficiency can cause severe toxicity. Testing before starting is recommended by international guidelines.
Severe bone marrow suppression: If your blood counts are already very low, 5-FU can reduce them further to a dangerous level.
Serious heart conditions: 5-FU has a known association with cardiac toxicity in some patients, including coronary artery spasm. A history of coronary artery disease is a factor your oncologist will consider carefully.
Severe liver impairment: 5-FU is processed by the liver, and severe impairment changes how the drug behaves in the body.
Pregnancy and breastfeeding: 5-FU can harm a developing baby and is not used during pregnancy or breastfeeding.

Eligibility is decided by your oncologist based on your individual history, blood tests, and cancer type. This list is not a substitute for that assessment.

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In detail

How bad do mouth sores get — and what about the hands and feet?

Mucositis means inflammation of the lining of the mouth and throat. With 5-FU, it typically appears a few days after each treatment and can range from mild sensitivity to painful ulcers that make eating and drinking difficult.

The most important thing you can do is tell your team at the first sign — even just a slightly sore or dry mouth. Treated early, mucositis usually stays manageable. Left unreported, it can worsen to the point where you cannot swallow enough fluids.

Hand-foot syndrome follows the same principle. At the first sign of redness, warmth, or tenderness in your palms or soles, tell your team. A moisturising routine and avoiding pressure on affected skin are part of early management — but that starts with reporting it.

Do not wait for your next scheduled appointment if either is bothering you. Both can worsen between cycles, and early contact changes the outcome.

Step by step

What happens during a 46-hour pump cycle, step by step?

You arrive at the clinic on your treatment day

The nursing team checks your blood results. If your counts are suitable, your port, PICC line, or central line is accessed.

The pump is connected to your line

The nurse attaches the sealed pump to your line. It is small — roughly the size of a small water bottle — and starts running automatically.

You leave with the pump in a carry bag

The pump sits in a small shoulder bag or belt pouch. You go home, eat, sleep, and move about normally while it runs.

You carry the pump for around 46 hours

You do not need to operate or adjust the pump. If it leaks, sounds an alarm, or the line comes loose, call your clinic — do not try to fix it yourself.

You return to the clinic for disconnection

The nurse disconnects and removes the pump in a few minutes. Your line is flushed and your next appointment is confirmed.

Worth knowing

Did you know?

Mouth sores and hand-foot syndrome are among the most underreported side effects of fluoropyrimidine chemotherapy. Patients often assume that discomfort is simply part of treatment and must be endured.

Neither has to be severe. Both respond to early intervention — and telling your team at the first sign of redness or soreness is the single most effective thing you can do.

Source: ESMO Clinical Practice Guidelines: Supportive Care in Oncology

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Common questions

Frequently asked questions

Why does the pump stay attached for 46 hours — can it be shorter?

The 46-hour duration is part of how the regimen is designed, not an arbitrary choice. Regimens such as FOLFOX and FOLFIRI, commonly used for colorectal and gastric cancers, were established through research that found continuous delivery over this period to be part of how the treatment works. Your oncologist prescribes the specific duration that applies to your case. Changing it without medical instruction would change the treatment itself, not just the convenience.

What can I eat when I have mouth sores?

Soft, cool, and non-acidic food is generally easier to manage when mucositis is active — things like well-cooked rice, yoghurt, banana, and soft dal. Very hot, spicy, or acidic food such as tomatoes and citrus, and rough or crunchy textures tend to worsen soreness. The most important step is telling your team early, because there are mouthwashes and medicines that help and work better when started before the soreness becomes severe. If you cannot swallow enough fluid in a day, call your team the same day rather than waiting.

What does hand-foot syndrome look like when it first starts?

In its early form, hand-foot syndrome shows as mild redness, a feeling of warmth, and slight tenderness in the palms of the hands and soles of the feet. The skin may look flushed or feel dry. This is the stage to tell your team — because at this point, moisturising, avoiding pressure, and sometimes adjusting treatment can keep it mild. Left unreported, it can progress to blistering, peeling, and pain that makes walking or gripping things difficult. Early is always better.

Will my hair fall out on 5-FU?

5-FU causes less hair loss than some other chemotherapy medicines, and significant hair loss is not a typical feature of 5-FU regimens. Some mild thinning can occur in some people. If you are receiving a combination regimen that includes other drugs — such as oxaliplatin or irinotecan — those drugs may also affect your hair, and the combination determines what to expect. Ask your oncologist which medicines are in your specific regimen, because the answer depends on what is being given alongside 5-FU, not on 5-FU alone.

What signs should make me call the clinic straight away?

Call the same day if you develop a fever — your team will give you a specific temperature threshold to watch for before treatment begins. Also call if you have severe or rapidly worsening diarrhoea, if you cannot keep fluids down because of nausea or mouth soreness, or if you notice chest pain, tightness, or palpitations. 5-FU has a known association with cardiac symptoms in some patients, and chest pain during treatment always needs urgent attention. If you are unsure whether something is serious, call rather than waiting — it is always the right default.

Can I drink alcohol or take other medicines while on 5-FU?

Alcohol can worsen nausea and mouth soreness, and your team may advise reducing or avoiding it during treatment. More importantly, some over-the-counter medicines, supplements, and herbal preparations interact with 5-FU or affect how it is processed in the body — including aspirin, ibuprofen, and certain commonly used supplements. Tell your team everything you are taking before you start, and ask before starting anything new. This includes Ayurvedic preparations, which should always be mentioned to your treating team even if you consider them safe or natural.

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