Chemotherapy is a drug treatment that kills fast-dividing cells throughout your body. What actually happens spans far more than the infusion itself: it includes preparation beforehand, hours in a treatment chair, a recovery period at home, and ongoing monitoring between sessions. If you or someone close to you is about to start chemo, here’s what the full process looks like from start to finish.
How Chemotherapy Drugs Attack Cancer
Cancer cells grow and divide faster than most normal cells, and chemotherapy exploits that vulnerability. Some drugs work by damaging DNA directly, essentially scrambling the genetic instructions a cell needs to copy itself. Others block the raw materials cells need to build new DNA, starving them during the replication process. A third category targets the physical machinery cells use to pull apart and divide.
Some of these drugs attack cells only during a specific phase of growth, such as when DNA is being copied or when the cell is actively splitting in two. Others damage cells regardless of what phase they’re in, including cells that are temporarily resting. This is why oncologists often combine multiple drugs into a single regimen: by hitting different stages of the cell cycle at once, fewer cancer cells escape.
The downside is that other fast-dividing cells in your body, like those lining your mouth, gut, and bone marrow, get caught in the crossfire. That overlap between cancer cells and healthy cells is the root cause of most chemotherapy side effects.
Before the Infusion Starts
Your care team will likely ask you to eat a light meal before arriving unless told otherwise. Wear something comfortable with easy access to your arm or chest, like a short-sleeved or button-up shirt. Plan to arrive about 15 minutes early.
At check-in, a nurse will take your weight, check your vital signs, and possibly draw blood. Blood work before each session is common because your team needs to confirm your blood cell counts and organ function are strong enough to handle the next dose. You may also sign a consent form, especially on your first visit.
Before the chemo drugs themselves, you’ll typically receive pre-medications through your IV. These often include anti-nausea drugs, a steroid to reduce inflammation and allergic reactions, and sometimes an antihistamine or anti-anxiety medication. For certain drugs known to cause infusion reactions, you might take a steroid by mouth the night before and the morning of treatment. These pre-medications make a significant difference: chemotherapy drugs that cause nausea in more than 10% of patients almost always come with preventive anti-nausea treatment built into the protocol.
What the Infusion Itself Is Like
A nurse will either start a standard IV in your hand or arm, or access a port if you have one. A port is a small device surgically placed under the skin of your chest, connected to a large vein. Ports reduce the need for repeated needle sticks, lower the risk of the drug leaking into surrounding tissue, and are generally more comfortable over months of treatment. If your regimen involves many sessions or drugs that are harsh on smaller veins, your oncologist will typically recommend a port before treatment begins.
Once the line is running, the nurse will let you know when the actual chemotherapy drug starts. Infusion times vary widely. Some drugs drip over 30 minutes, others take several hours. A full session, including pre-medications, the chemo drugs, and any fluids given afterward, can last anywhere from one to six or more hours. During that time, you’re free to read, watch something on your phone, nap, or talk. Many treatment centers have recliners, blankets, and Wi-Fi available.
Nurses will check your vital signs at regular intervals and watch for reactions. Immediate reactions, when they happen, tend to appear within the first 15 minutes and can include flushing, itching, shortness of breath, or changes in blood pressure. These are uncommon, and nearly all of them resolve within an hour once the infusion is paused and treated. Most people get through their sessions without any acute reaction.
The Cycle Structure
Chemotherapy is given in cycles: a period of treatment followed by a period of rest. A common pattern is one week of treatment followed by three weeks off, making a four-week cycle. Some regimens use two-week or three-week cycles, and the number of total cycles depends on the type and stage of cancer.
The rest period isn’t optional. It exists because your healthy cells need time to recover, especially the blood-forming cells in your bone marrow. Without that break, cumulative damage to normal tissue would become dangerous. Your oncologist plans each cycle so that your body has rebuilt enough healthy cells before the next round hits.
Side Effects and When They Appear
Side effects don’t all arrive at once. They follow a rough timeline that repeats with each cycle.
In the first 24 hours, nausea is the most common concern, though pre-medications prevent or significantly reduce it for most people. You may also feel fatigued, flushed, or have a metallic taste in your mouth. Some people feel surprisingly fine on day one.
Over the next one to two weeks, deeper effects set in. Your bone marrow slows its production of blood cells, and counts typically hit their lowest point around 10 to 17 days after treatment. White blood cells drop first, which temporarily weakens your immune system. Platelets, which help your blood clot, follow a similar pattern. This low point is called the nadir, and it’s the window when you’re most vulnerable to infections and bleeding. Your care team may schedule blood draws during this period to monitor your counts.
Hair loss, mouth sores, digestive changes, and skin sensitivity tend to develop gradually over the first few cycles rather than appearing all at once. Not every drug causes every side effect. Your oncologist can tell you which ones are most likely based on your specific regimen.
Safety Precautions at Home
For at least 48 hours after each infusion, traces of the chemotherapy drugs are present in your body fluids, including urine, stool, and vomit. During this window, caregivers should wear gloves when handling soiled linens, cleaning up body fluids, or changing diapers. Keep the toilet lid down when flushing, and wash contaminated laundry separately. These are straightforward precautions that protect the people around you from low-level drug exposure.
How Doctors Track Whether It’s Working
Your oncologist won’t wait until the end of all your cycles to check progress. Imaging scans, blood tests, or both are used at intervals during treatment to see how the cancer is responding. For solid tumors, doctors measure target lesions on scans and categorize the result into one of four outcomes: complete response (the tumor has disappeared on imaging), partial response (at least a 30% reduction in tumor size), stable disease (no significant change), or progressive disease (the tumor has grown by 20% or more). Blood-based cancers are tracked through lab markers instead.
If scans show the cancer is shrinking or stable, treatment typically continues as planned. If the disease is progressing, your oncologist may switch to a different drug combination.
Long-Term Effects After Treatment Ends
Some effects of chemotherapy persist or even emerge months to years after the last infusion. About one-third of cancer survivors experience significant fatigue up to six years after finishing treatment. Cognitive changes, sometimes called “chemo brain,” can affect memory, concentration, and mental processing speed across a range of cancer types. And for certain drugs, nerve damage can be lasting: roughly 21% of colorectal cancer patients treated with one common regimen still report pain or numbness in their feet five years later.
Fear of the cancer returning is another well-documented aftereffect. Depending on how it’s measured, between 20% and 58% of survivors report clinically meaningful levels of this anxiety years after treatment. These physical and emotional late effects often overlap and reinforce each other, which is why survivorship care, including follow-up visits focused on quality of life, has become a growing part of cancer treatment planning.