Chemotherapy is not a single drug. A typical chemo session delivers a mix of cancer-killing chemicals, anti-nausea medications, steroids, and carrier fluids, all tailored to the specific type and stage of cancer being treated. What ends up in your IV bag or pill bottle depends on your diagnosis, but the core ingredients fall into a few well-defined categories.
The Cancer-Killing Drugs
The active ingredients in chemotherapy are cytotoxic chemicals, meaning they kill cells that are actively dividing. Since cancer cells divide faster than most normal cells, they’re hit hardest. These drugs work by interrupting different stages of cell division, and they generally fall into a few major classes.
Alkylating agents are compounds that form permanent chemical bonds with DNA, physically preventing a cell from copying its genetic material. The most common type, nitrogen mustards, contain a reactive chemical group that latches onto DNA strands and locks them together. Platinum-based drugs work similarly: a platinum atom at the center of the molecule swaps out its original chemical attachments for bonds with DNA, creating cross-links that stop the cell from replicating. These drugs don’t wait for a specific phase of cell division, so they can affect cells at multiple points.
Antimetabolites are designed to mimic the building blocks cells need to copy their DNA. When a cell tries to use these fake building blocks during DNA synthesis, the process stalls. This makes antimetabolites most effective during the phase when cells are actively building new DNA.
Plant-derived drugs come from two surprising sources. Vinca alkaloids, originally extracted from the Madagascar periwinkle flower, and taxanes, derived from the Pacific yew tree, both work by disrupting the tiny structural fibers a cell needs to physically pull apart during division. Without those fibers, the cell can’t split in two, and it dies.
Why Chemo Uses Drug Combinations
Most chemotherapy isn’t a single drug. Oncologists combine multiple agents into regimens, each known by an acronym. ABVD, used for Hodgkin lymphoma, contains four drugs: doxorubicin, bleomycin, vinblastine, and dacarbazine. R-CHOP, a standard regimen for certain lymphomas, combines five: rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone. FOLFOX pairs a platinum drug with an antimetabolite for colon cancer.
The logic is straightforward. Each drug attacks the cell cycle at a different point, so combining them makes it harder for cancer cells to survive. One drug might damage the DNA while another prevents the cell from repairing it. Combinations also reduce the chance that cancer develops resistance to any single agent.
How Your Dose Is Calculated
The amount of each drug you receive is based on your body surface area, a measurement derived from your height and weight. This practice dates back to early cancer research, when scientists found that body surface area was a better predictor of how a drug would behave in the body than weight alone. At least five different formulas exist for this calculation, and oncologists typically use whichever is standard at their institution. For patients who are clinically obese, current guidelines recommend using actual body weight rather than an idealized number. In practice, the final dose is often rounded to the nearest convenient amount.
What Else Is in the IV Bag
The active drug makes up only a small fraction of what flows through your IV. The rest is carrier fluid, most commonly normal saline (a sterile solution of sodium chloride in water) or a 5% dextrose solution, essentially sterile sugar water. These fluids dissolve the drug, keep it stable, and deliver it at a safe concentration. Small amounts of hydrochloric acid or sodium hydroxide may be added to adjust the solution’s pH so it doesn’t irritate your veins.
Some chemotherapy vials also contain preservatives. Benzyl alcohol, for example, appears in certain formulations of methotrexate at a concentration of about 0.9%. This prevents bacterial growth in multi-dose vials. However, preservative-free versions are required for drugs injected into the spinal fluid, where even small amounts of benzyl alcohol can cause serious neurological harm.
Medications Given Before and During Infusion
Before the actual chemotherapy starts, you’ll typically receive a round of premedications through the same IV line. These aren’t optional extras. They prevent the most disabling side effects of treatment.
Anti-nausea drugs are the most important. Chemotherapy regimens are rated by how likely they are to cause vomiting, and the premedication cocktail scales accordingly. For highly nauseating regimens, you’ll receive three or four anti-nausea drugs working through different pathways in the brain. For milder regimens, a single agent may be enough. The steroid dexamethasone plays a dual role: it reduces nausea on its own and boosts the effectiveness of the other anti-nausea medications. You might receive 12 mg on infusion day and 8 mg on the days following.
Some chemotherapy drugs can trigger allergic-type reactions during the infusion, so acetaminophen and antihistamines are commonly given beforehand as a precaution. For certain drugs like docetaxel, you may start taking oral steroids the day before your infusion, continuing for three days total, to prevent fluid retention and allergic reactions.
What’s in Chemo Pills
Not all chemotherapy comes through an IV. Oral chemotherapy pills contain the same types of active cytotoxic ingredients, packaged with the same inactive fillers found in any tablet. These include binders that hold the pill together, coatings that control how quickly it dissolves, and lubricants that keep it from sticking to manufacturing equipment. Magnesium stearate, a common lubricant, appears in roughly 72% of all oral medications on the market. Some pills contain lactose as a filler, which can be relevant for people with severe dairy allergies since the lactose may carry trace milk protein contamination.
Targeted Therapy vs. Traditional Chemo
If your oncologist mentions targeted therapy, the ingredients are fundamentally different from traditional chemotherapy. Traditional chemo uses potent chemicals that kill any rapidly dividing cell, cancerous or not. Targeted therapies are either small synthetic molecules designed to slip inside cells and block a specific protein driving tumor growth, or laboratory-made antibodies (large protein molecules) that attach to markers on the surface of cancer cells.
The distinction matters because it changes the side effect profile. Traditional cytotoxic drugs damage healthy tissue in the gut, bone marrow, and hair follicles because those cells also divide quickly. Targeted therapies are more selective, though they come with their own set of side effects depending on which molecular pathway they block. Many modern treatment plans combine both approaches, using traditional chemo to kill the bulk of the tumor while targeted agents cut off specific survival signals the cancer depends on.