When Do Chemotherapy — Side Effects Start?

Nausea can begin within hours of your infusion, particularly once the anti-nausea medicines given during treatment begin to wear off. A second wave called delayed nausea can appear one to three days later and is common with certain regimens — your team can prescribe medicines to cover both phases. If nausea is stopping you from eating or drinking, call your team the same day, as dehydration develops quickly and is treatable when caught early.

The general pattern — effects within hours, harder days in the first week, recovery heading into the next cycle — applies to most people, but the exact days vary by regimen and by the individual. Some have their hardest day on day two, others on day four or five. After the first cycle you will know your own pattern, which makes it much easier to plan around the more difficult days.

Call the same day for fever, breathlessness, bleeding, severe pain, or anything that feels serious or is worsening quickly. Fever in the week or two after treatment — when white cell counts are at their lowest — is always a same-day call even if it seems mild. For uncomfortable but non-urgent symptoms, many teams have a nurse helpline. If you are unsure whether a symptom warrants a call, the safe default is to call.

Some effects are cumulative, building with each dose rather than appearing after a single treatment. Peripheral neuropathy — the tingling or numbness in hands and feet associated with certain medicines — is the most common example. You may notice nothing after the first two cycles and then begin to feel it later. This is why your team monitors you between cycles and not only at the start and end of your course.

Unlikely. Side effects vary by the specific medicines in your regimen and by your individual response. The list your team gives you describes what is possible, not what will definitely happen to you. Many people experience a handful of effects, often milder than they feared. Ask your team which effects are common with your specific regimen and which are rare — that gives a more useful picture than a general list.

For most people, fatigue peaks in the one to three days after treatment rather than on the day of the infusion, then eases as the body recovers toward the next cycle. Fatigue that stops you getting out of bed or managing basic daily tasks is worth reporting to your team. It can sometimes be linked to anaemia or other treatable causes, and there are strategies that help even when no specific cause is found.