Crohn's Disease Forum » Forum Wiki » 6-Mercaptopurine


Also known as 6-Mercaptopurine, 6-MP, and Purinethol (brand name).

Mercaptopurine is in a class of medications called thiopurines and is an immunomodulator. It works by altering the immune response by inhibition of natural killer cell activity and suppression of T-cell function. Immunomodulators are used to help decrease corticosteroid dosage and also to help heal fistulas. In addition, immune modifiers can help maintain disease remission and have been shown to be more effective than steroids in this role.[1] It may take 2-3 months for results to be seen.



The maintenance dose of 6-MP tends to be 1-1.5 mg/kg. However, weight based dosing has been shown to correlate poorly with 6-TGN levels which are thought to correlate with the therapeutic affect of 6-MP. As such, 6-TGN levels should be monitored. It has been shown that splitting a dose to morning and evening can help lower 6-MMP levels while maintaining 6-TGN levels.[2]

Consuming milk products around the time you take your dose can potentially interfere with the bioavailability of 6-MP. It is best to avoid milk products for at least 2 hours before and after your dose.[3]

Possible Side Effects:

  • Nausea
  • Vomiting
  • Darkening of the skin
  • Hair loss
  • Fever
  • Leukopenia (decrease in white blood cells)
  • Rash
  • Pale skin
  • Weakness
  • Dizziness/fainting
  • Shortness of breath
  • Sore throat, fever, chills, or other signs of infection
  • Unusual bruising or bleeding
  • Yellowing of the skin or eyes
  • Pancreatitis (3-15% of patients)
  • Hepatitis
  • Loss of appetite
  • Diarrhea
  • Swelling of the stomach area
  • Pain in the upper right part of the stomach
  • Joint pain/swelling
  • Increased risk of lymphoma
  • Increased MCV

Blood Monitoring

If you are taking/prescribed 6-MP you must have blood work done on a regular basis (could be once/week, once/month or every few months) to make sure that you are not experiencing serious side effects. Talk to your doctor about how often and why you need to have blood work done.

Azathioprine as An Alternative

There is evidence that those who are intolerant to Azathioprine may do better on 6-MP. Unfortunately, data does not support the reverse being true, likely because Azathioprine is cleaved to 6-MP in the body.[2]


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