Skip to main content
Cancer Explained
Donate

Based on National Cancer Institute resources

Side effects, explained

Plain-language explainers on the side effects of cancer and its treatment — what they are, why they may happen, and questions to bring to your care team.

A note before you read: this is educational information, not medical advice. Side effects vary from person to person — even among people receiving the same treatment. Your health care team is the right source for advice about your situation.

Some side effects can’t wait

Most side effects can be discussed at your next visit — but a few mean call your care team now, day or night. Based on CDC and National Cancer Institute guidance, these include:

  • Fever of 100.4°F (38°C) or higher, or shaking chills — during chemotherapy a fever is a medical emergency: call immediately, at any hour.
  • Vomiting or diarrhea that won’t stop, or being unable to keep liquids down — dehydration can develop fast.
  • Bleeding that doesn’t stop, or blood in vomit, stool, or urine.
  • New trouble breathing, chest pain, or sudden confusion — call 911 or your local emergency number.

Your care team may give you a different temperature threshold or after-hours number — their instructions come first. Learn more in Fever During Chemotherapy and Infection and Neutropenia.

Body changes

Pain, nerves, swelling, fertility, and sexual health.

Side-effect help doesn’t all live in one place. These guides from our nutrition, symptoms, and living-with-cancer sections pick up where the explainers above leave off.

Eating and drinking

When nausea, mouth sores, or a vanished appetite make food hard, these guides offer small, practical ideas — no pressure, no perfect diets.

Side effect, or something more?

Not every new symptom is a side effect — and not every side effect is 'just' a side effect. When you're unsure, these can help you sort out what's worth a call.

The heavy days

Side effects aren't only physical. Worry, low mood, and exhaustion are real parts of treatment too — and there's help for those as well.

Wondering about a specific medicine?

Many side effects come from a particular drug. Our medicine guides explain what each one is, its common side effects, and the warning signs to report.

Turn reading into a conversation

Every explainer includes questions for your care team. These tools help you get ready for your next appointment.

More ways in

Browse all nutrition during treatment guides, look up a drug in cancer medicines, explained, bring your side-effect questions to the appointments hub, or — if you’re helping someone through this — start at the caregiving hub.