Medical Oncologist
Your first cycle
Infusion reactions: what they are and what happens
The body reacting to a drug as it goes in, usually within the first minutes of a new medicine starting — flushing, itching, a rash, a tight chest, breathlessness, shivering or feeling suddenly unwell. They are uncommon, and they almost always happen where they can be dealt with immediately. Most settle quickly and the treatment continues the same day, more slowly.
NG
Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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The short answer
What is an infusion reaction?
The body reacting to a drug as it goes in, usually within the first minutes of a new medicine starting. It shows as flushing, itching, a rash, a tight chest, breathlessness, shivering, back pain or feeling suddenly unwell. It is not the same as the side effects that appear over the following days.
They are uncommon with most drugs, they are more likely with a few specific ones, and they almost always happen where they can be dealt with immediately — in a chair, with a nurse in the room, watching for exactly this.
The reassuring part
Most reactions are mild, settle quickly once the infusion is paused and something is given, and the treatment then continues the same day, usually running more slowly. Having a reaction does not normally mean the drug is abandoned.
Press the call bell the moment something feels wrong. Do not wait to see whether it passes, and do not wait for the nurse to walk by.
!
Call the nurse immediately for any of these
Breathlessness or a tight chest · a rash, flushing, itching or hives · a swollen face, lips or tongue · feeling suddenly hot, faint or very unwell · pain in the back, chest or stomach · shivering, or feeling feverish · dizziness or a racing heart · pain, burning or swelling at the drip site. Press the call bell. Say what you are feeling rather than trying to decide whether it counts — that judgement is theirs to make, and they would far rather be called for nothing.
Not sure whether this applies to you?
Ask an oncologistIf it happens
What the team actually does
This is a well-drilled routine rather than an emergency improvisation, and it usually takes minutes.
The infusion is stopped
First and immediately. The drip is paused and the line is flushed, so no more of the drug goes in while you are assessed.
You are checked over
Pulse, blood pressure, oxygen level, breathing and your skin. Usually within moments, and often by more than one person, which can look alarming and is simply how it is done.
Medicine is given to settle it
Usually through the same line — antihistamines, steroids, sometimes other medicines depending on what is happening. Most reactions settle quickly once this is given.
You are watched for a while
Until things are clearly stable. This lengthens the day, which is worth knowing so that whoever is collecting you is not left waiting without explanation.
The infusion is usually restarted
Often at a slower rate, sometimes with extra pre-medication. In most cases the same treatment is completed that day rather than abandoned.
What it means going forward
Does it change the rest of your treatment?
Usually less than people fear. For most mild reactions, the plan for future cycles is more pre-medication and a slower infusion rate, and subsequent cycles pass without incident. Many people have a reaction on a first exposure and none afterwards.
When it does change things
A severe reaction, or one that recurs despite extra pre-medication, may lead your oncologist to switch to a different drug. That is a considered decision made to keep you safe, and it is not the same as running out of options — there is usually an alternative.
Make sure it is recorded properly
Ask for the reaction to be written in your file and on your treatment card, with the drug name and what happened. Ask for a copy. If you are ever treated elsewhere, or seen by a doctor who does not know you, that record matters a great deal.
Tell them at every future cycle
Even if it is in the notes. Say it at registration and again when the line is being set up. Staff change, and a sentence from you is the most reliable safeguard there is.
Ask what you should watch for at home afterwards, and for how long. Delayed reactions are uncommon but they do happen.Leave a number, we will call you
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Lowering the chance
What already reduces the risk
Most of this is done for you. Knowing about it explains why the day is structured the way it is.
Pre-medication
Antihistamines and steroids given before the chemotherapy exist substantially for this reason. This is why they are given to everyone, including people who have never reacted.
Which is why
- Never ask for them to be skipped
- Take any pre-cycle tablets as instructed
A slow start
Drugs known to cause reactions are often started slowly and speeded up if all is well. That is why the first bag of a new drug takes longer than later ones.
Close observation early on
The nurses check on you more often in the first minutes of a new drug, because that is when reactions usually appear. It is deliberate rather than a sign of concern about you.
Stay in the chair during that period rather than wandering off.Telling them your history
Previous drug reactions, allergies, asthma, and any reaction to a previous cycle. Say all of it before the line is set up, every time, rather than assuming it is on file.
Being straight with you
What this page cannot tell you
It cannot tell you how likely a reaction is for you. That depends heavily on which drugs you are having — some carry a meaningful chance and many carry almost none. Ask your own team whether yours is one to watch for, and what they will be doing about it.
It also cannot tell you whether something you are feeling is a reaction. Coolness in the arm, a taste in the mouth and drowsiness are ordinary; breathlessness, rash and swelling are not. When you are not sure, the answer is to call the nurse rather than to work it out.
What to do next
Before your first cycle, ask whether your drugs commonly cause reactions and what will be done to reduce the chance. Tell the team about any allergies or previous drug reactions every time, not just once. Learn where the call bell is. And if you have had a reaction, get it written on your card and carry it.
Questions we are asked
Common questions about infusion reactions
How common are they?
Uncommon with most chemotherapy drugs, and more likely with a few specific ones. Ask your team whether yours is one to watch for. What is reassuring is that they nearly always happen in the unit, where a nurse is watching and the response is immediate.
Will the treatment be stopped for good?
Usually not. Most mild reactions are settled with medicine and the same infusion is restarted more slowly the same day. Future cycles typically go ahead with extra pre-medication. Only a severe or recurring reaction leads to a change of drug, and there is usually an alternative.
Is a reaction the same as an allergy?
Not always, though they can look similar. Some reactions are true allergic responses and others are the body reacting to the infusion itself, which is why many people can continue the same drug afterwards. Your team distinguishes them; from the chair they feel much the same.
When do they usually happen?
Most often within the first minutes of a new drug starting, which is why nurses check on you closely then and why the first bag runs slowly. Reactions later in an infusion, or after you get home, are less common but do occur — ask what to watch for.
What if I am not sure whether it counts?
Call the nurse anyway. Deciding whether a symptom matters is their job, not yours, and they would far rather come for nothing than be called late. Describe what you feel plainly rather than trying to judge whether it is significant.
Can a reaction happen after I get home?
Delayed reactions are uncommon but possible. Ask what to watch for and for how long before you leave. A rash, breathlessness, swelling of the face or lips, or feeling suddenly very unwell at home should be treated as urgent — go to the nearest emergency department and say you are on chemotherapy.
Should I mention a reaction I had years ago to another drug?
Yes, always, and every time rather than once. Previous drug reactions, allergies and asthma all matter here, and staff change between cycles. A sentence from you at the chair is the most reliable safeguard, whatever is written in the file.
Does a reaction mean the drug is not working?
No. The two are unconnected. A reaction is about how your body responds to the drug going in, not about whether it is acting on the cancer. Whether the treatment is working is judged on scans and tests at the planned points.
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Sources
- Cancer Research UK — Having chemotherapy
- National Cancer Institute — Chemotherapy to Treat Cancer
- Macmillan Cancer Support — Having chemotherapy
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
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