Purinethol (Mercaptopurine) - Oral

What Is Purinethol?

Purinethol (mercaptopurine, 6-MP) is an oral chemotherapy medication used to treat acute lymphoblastic leukemia (ALL). Purinethol is a nucleoside metabolic inhibitor that belongs to the class of drugs called antimetabolites. Antimetabolites help stop the growth of cancer cells.

This medication comes in tablet form. It is also available as a suspension (liquid) under the brand name Purixan.

Drug Facts

Generic Name: Mercaptopurine (6-MP)

Brand Name(s): Purinethol, Purixan

Drug Availability: Prescription

Administration Route: Oral

Therapeutic Classification: Antineoplastic agent

Available Generically: Yes

Controlled Substance: N/A

Active Ingredient: Mercaptopurine

Dosage Form: Tablet, suspension

What Is Purinethol Used For?

Purinethol is used in combination with other chemotherapy as part of a treatment regimen for adults and children with ALL.

ALL is a type of leukemia that commonly occurs in children. However, adults can develop ALL as well. It is sometimes referred to as acute lymphocytic or acute lymphoid leukemia, and it affects a type of white blood cell called immature lymphocytes, also known as blasts.

An illustration with drug information about Purinethol (mercaptopurine 6-MP)

Illustration by Dennis Madamba for Verywell Health

How to Take Purinethol

This medication is usually taken once a day, around the same time. No specific time of day is recommended in the prescription label for taking Purinethol; however, studies have demonstrated better outcomes with an evening schedule versus a morning schedule for children treated for ALL.

For both the tablet and suspension form, you can take it with or without food, but you should consistently take it the same way.

Although there is no specific time of day recommended in the prescribing label for Purinethol

If you are taking the suspension form (Purixan), make sure to use the provided syringes that come with the medication so that you administer the correct dose. Shake the suspension well for 30 seconds before each dose. After using, wash the syringe in warm, soapy water and allow it to fully dry before using it again. Make sure to discard the suspension within eight weeks of opening the bottle.


Store Purinethol at room temperature, in its original container. Do not put the tablets in a pill box. This is a hazardous chemotherapy medication that should be kept out of the reach of children and pets.

Store the suspension formulation in a clean, dry place. Properly dispose of any unused medication after eight weeks. 

Make sure to follow special precautions when handling hazardous medications at home. Only the person prescribed the medication should handle it, if possible. If a caregiver needs to handle it, they should wear disposable gloves. Wash your hands after touching the medication or removing the gloves.

Off-Label Uses

Healthcare providers can prescribe medications off-label for medical conditions that are not yet approved by the Food and Drug Administration (FDA). 

Purinethol has been prescribed for off-label use to treat Crohn’s disease and ulcerative colitis.

What Are the Side Effects of Purinethol?

This is not a complete list of side effects and others may occur. A healthcare provider can advise you on side effects. If you experience other effects, contact your healthcare provider. You may report side effects to the FDA at fda.gov/medwatch or 1-800-FDA-1088.

Common Side Effects

Common side effects of Purinethol can include:

Severe Side Effects

Some side effects from 6-MP can be severe. Call your healthcare provider right away if you’re experiencing any serious side effects. Call 911 if you feel you are having a life-threatening medical emergency.

Serious side effects and their symptoms can include:

  • Severely low blood counts
  • Liver dysfunction or failure
  • Macrophage activation syndrome, which can cause fever, severely low blood counts, and blood clots

Long-Term Side Effects

The use of 6-MP is associated with the risk of developing other cancers in the future, such as:

Report Side Effects

Purinethol may cause other side effects. Call your healthcare provider if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your healthcare provider may send a report to the FDA's MedWatch Adverse Event Reporting Program or by phone (800-332-1088).

Dosage: How Much Purinethol Should I Take?

Drug Content Provided and Reviewed by IBM Micromedex®

The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For oral dosage forms (suspension or tablets):
    • For maintenance treatment of acute lymphatic leukemia:
      • Adults—Dose is based on body weight and must be determined by your doctor. At first, 1.5 to 2.5 milligrams (mg) per kilogram (kg) of body weight per day, taken as a single dose. Your doctor may adjust your dose as needed and tolerated.
      • Children—Use and dose must be determined by your doctor.


In certain cases, your healthcare provider may modify your treatment with 6-MP. For example, if you have severe side effects or severely low blood counts, your healthcare provider may change your dose.

Missed Dose

If you miss a dose, take it as soon as it is remembered. However, if it is close to the next dose due, skip the missed dose. Never double up on a dose, even if one was missed.

Overdose: What Happens If I Take Too Much Purinethol?

An overdose of Purinethol may cause symptoms, such as:

  • Nausea
  • Vomiting
  • Diarrhea
  • Liver dysfunction
  • Low blood counts

If an overdose is suspected, contact your healthcare team immediately, as there may be the potential need to induce vomiting to reduce the risk of an overdose.

What Happens If I Overdose on Purinethol?

If you think you or someone else may have overdosed on Purinethol, call a healthcare provider or the Poison Control Center (800-222-1222).

If someone collapses or isn't breathing after taking Purinethol, call 911 immediately.


Drug Content Provided and Reviewed by IBM Micromedex®

It is very important that your doctor check your progress at regular visits to make sure that this medicine is working properly. Blood tests may be needed to check for unwanted effects. Genetic testing may also be performed to check your levels of thiopurine S-methyltransferase (an enzyme needed to metabolize mercaptopurine).

Using this medicine while you are pregnant can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant during treatment with this medicine and for at least 6 months after your last dose. Male patients who have female partners should use effective birth control during treatment with this medicine and for at least 3 months after the last dose. If you think you have become pregnant while using this medicine, tell your doctor right away.

Mercaptopurine can temporarily lower the number of white blood cells in your blood, increasing the chance of getting an infection. It can also lower the number of platelets, which are necessary for proper blood clotting. If this occurs, there are certain precautions you can take, especially when your blood count is low, to reduce the risk of infection or bleeding:

  • If you can, avoid people with infections. Check with your doctor immediately if you think you are getting an infection or if you get a fever or chills, cough or hoarseness, lower back or side pain, or painful or difficult urination.
  • Check with your doctor immediately if you notice any unusual bleeding or bruising, black, tarry stools, blood in the urine or stools, or pinpoint red spots on your skin.
  • Be careful when using a regular toothbrush, dental floss, or toothpick. Your medical doctor, dentist, or nurse may recommend other ways to clean your teeth and gums. Check with your medical doctor before having any dental work done.
  • Do not touch your eyes or the inside of your nose unless you have just washed your hands and have not touched anything else in the meantime.
  • Be careful not to cut yourself when you are using sharp objects such as a safety razor or fingernail or toenail cutters.
  • Avoid contact sports or other situations where bruising or injury could occur.

Check with your doctor right away if you have pain or tenderness in the upper stomach, pale stools, dark urine, loss of appetite, nausea, vomiting, or yellow eyes or skin. These could be symptoms of a serious liver problem.

While you are being treated with mercaptopurine, and after you stop treatment with it, do not have any immunizations (vaccines) without your doctor's approval. Mercaptopurine may lower your body's resistance and the vaccine may not work as well or you might get the infection the vaccine is meant to prevent. In addition, you should not be around other persons living in your household who receive live virus vaccines because there is a chance they could pass the virus on to you. Some examples of live vaccines include measles, mumps, influenza (nasal flu vaccine), poliovirus (oral form), rotavirus, and rubella. Do not get close to them and do not stay in the same room with them for very long. If you have questions about this, talk to your doctor.

This medicine may increase your risk of getting certain types of cancer, including skin cancer and cervical cancer. Some teenagers and young adults with Crohn's disease or ulcerative colitis developed a rare type of cancer called hepatosplenic T-cell lymphoma (HSTCL). Check with your doctor right away if you have unusual bleeding, bruising, or weakness, swollen lymph nodes in the neck, underarms, or groin, or unexplained weight loss.

This medicine may cause a life-threatening condition called macrophage activation syndrome (MAS). This usually occurs in patients with an autoimmune disease (eg, inflammatory bowel disease) or virus infection (eg, Epstein-Barr, cytomegalovirus), and must be treated immediately. Tell your doctor right away if you have a fever, cough that does not go away, redness in one part of your body, or warm feeling or swelling of your skin.

Talk with your doctor before using this medicine if you plan to have children. Some men and women using this medicine have become infertile (unable to have children).

This medicine may make your skin more sensitive to sunlight. Wear sunscreen. Do not use sunlamps or tanning beds.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

What Are Reasons I Shouldn’t Take Purinethol?

You should not take Purinethol if you are pregnant or breastfeeding. Also, do not take this medication if you have an allergy to Purinethol or any of its ingredients.

What Other Medications Interact With Purinethol?

You may need to avoid certain medications if taking Purinethol. Taking some medications with Purinethol may also affect how well they work. You may need a dosage change for your Purinethol in some cases.

Medications that can interact with Purinethol include:

  • Allopurinol: You may need a reduced dose of Purinethol.
  • Warfarin: This combination may decrease the effectiveness of warfarin.
  • Bactrim (trimethoprim-sulfamethoxazole)
  • Mesalamine
  • Sulfasalazine
  • Medications that can cause liver toxicity

What Medications Are Similar?

Purinethol is in the class of chemotherapy medications called antimetabolites.

Other chemotherapy agents in this class include:

Frequently Asked Questions

  • What is Purinethol used for?

    Purinethol is an oral chemotherapy medication used to treat acute lymphoblastic leukemia (ALL). It is typically given in combination with other chemotherapy medications. Purinethol has off-label uses in Crohn’s disease and ulcerative colitis.

  • What drugs should not be taken with Purinethol?

    Certain medications may interact with Purinethol when taken together. These include:

    • Warfarin
    • Allopurinol
    • Sulfasalazine
    • Sulfamethoxazole and trimethoprim
  • What are the side effects of Purinethol?

    The side effects of Purinethol can include:

    • Low blood counts
    • Nausea
    • Vomiting
    • Diarrhea
    • Fatigue
    • Loss of appetite
    • Rash
    • Itching
    • Kidney dysfunction
    • Liver dysfunction

How Can I Stay Healthy While Taking Purinethol?

If you’ve been prescribed Purinethol, it is for a very important reason. Be sure to ask your healthcare team about what to expect as you begin treatment. 

If you do have side effects, do not stop taking your medication without talking to your healthcare provider. They may be able to help you manage your side effects.

Receiving a diagnosis of ALL can be scary and overwhelming. Keeping in constant communication with your healthcare team can help you better navigate your condition and treatment plan. You can also reach out to loved ones for emotional support to get you through this difficult time.

Medical Disclaimer

Verywell Health's drug information is meant for educational purposes only and is not intended to replace medical advice, diagnosis, or treatment from a healthcare provider. Consult your healthcare provider before taking any new medication(s). IBM Watson Micromedex provides some of the drug content, as indicated on the page.

8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Schmiegelow K, Glomstein A, Kristinsson J, Salmi T, Schrøder H, Björk O. Impact of morning versus evening schedule for oral methotrexate and 6-mercaptopurine on relapse risk for children with acute lymphoblastic leukemia. J Pediatr Hematol Oncol. 1997;19(2):102-109. doi:10.1097/00043426-199703000-00002

  3. Memorial Sloan Kettering Cancer Center. Safe handling of chemotherapy and biotherapy at home.

  4. Parelsnoer Institute (PSI), the Dutch Initiative on Crohn's and Colitis (ICC), Simsek M, et al. Off-label prescriptions of drugs used for the treatment of Crohn's disease or ulcerative colitis. Aliment Pharmacol Ther. 2019;49(10):1293-1300. doi:10.1111/apt.15229

  5. Crayne CB, Albeituni S, Nichols KE, Cron RQ. The immunology of macrophage activation syndrome. Front Immunol. 2019;0. doi: 10.3389/fimmu.2019.00119

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  7. Food and Drug Administration. Purinethol label.

  8. American Cancer Society. How chemotherapy drugs work.

By Julie Scott, MSN, ANP-BC, AOCNP
Julie is an Adult Nurse Practitioner with oncology certification and a healthcare freelance writer with an interest in educating patients and the healthcare community.