Mercaptopurine (6-MP)

Say it: mer-kap-toh-PYOOR-een · Brand names: Purixan

Mercaptopurine is a chemotherapy pill that blocks leukemia cells from making the DNA they need to grow.

What it is

Mercaptopurine looks like one of the building blocks of DNA. Leukemia cells take it in and cannot make DNA the right way. The cells stop growing and die.

Often used for

• acute lymphoblastic leukemia (ALL), as long-term maintenance treatment

How you get it

Mercaptopurine is a tablet or liquid you take at home, usually once a day, often for many months. Your team adjusts the dose based on your blood counts. Your schedule may be different.

Common side effects and what helps

• Low blood counts, which raise your risk of infection and bleeding. Wash your hands often.
• Nausea or vomiting. Take it the same way every day, and ask about anti-nausea medicine.
• Poor appetite. Try small meals.
• Feeling tired. Rest when you need to.
• Mouth sores. Use a soft toothbrush and gentle rinses.
• Rash. Use a gentle, unscented lotion.
• Changes in liver blood tests.

Call your care team right away if you have

• A fever of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher, or chills
• Yellow skin or eyes, dark urine, or belly pain
• Bleeding or bruising that will not stop, black or bloody stools, or blood in your urine
• Vomiting so much you cannot keep the medicine or fluids down
• Severe belly or back pain

Before you start, tell your team

• If you are pregnant, may become pregnant, or are breastfeeding
• If you take allopurinol or febuxostat for gout
• If you take warfarin
• If you have liver or kidney problems
• If you have had a test for TPMT or NUDT15 genes
• All the medicines, vitamins, and herbal products you take

Good to know

• Some people have gene changes (TPMT or NUDT15) that make this medicine much stronger. Your team may test for these.
• Allopurinol and febuxostat can raise the level of this medicine a lot. Your team must know if you take them.
• You will have blood tests often to check your blood counts and liver.
• Protect your skin from the sun, since it may raise skin cancer risk.

At home

• Take it at the same time each day, the same way each day (always with food or always without). Follow your team's plan.
• If you use the liquid, shake well and measure with the oral syringe from the pharmacy.
• If you miss a dose, ask your team what to do.
• Store at room temperature, away from children and pets.
• Caregivers should wear gloves if they touch the medicine and wash hands after.

Questions to ask

• Should I take it with or without food?
• Do I need gene testing before starting?
• How often will I need blood tests?
• Which of my medicines could interact with it?

Part of these treatment plans

• C10403 (CALGB 10403)
• POMP

Side effect guides

• Fatigue (tiredness)
• Nausea and vomiting
• Mouth sores
• Appetite loss and weight loss
• Low white blood cells and infection risk
• Low platelets and bleeding
• Skin rash (including EGFR-inhibitor rash)

Last updated: 2026-10-27. Medically reviewed by Veli Bakalov, MD, medical oncologist (October 2026). General education from Step by Step, the patient portal of HemeOncBuddy.