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Mercaptopurine Side Effects

Medically reviewed by Last updated on Nov 24, 2022.

Applies to mercaptopurine: oral suspension, oral tablet.

Serious side effects of Mercaptopurine

Along with its needed effects, mercaptopurine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking mercaptopurine:

More common

  • Black, tarry stools
  • bleeding gums
  • clay colored stools
  • cough or hoarseness
  • dark urine
  • decreased appetite
  • fever or chills
  • headache
  • loss of appetite
  • lower back or side pain
  • nausea, vomiting
  • painful or difficult urination
  • pale skin
  • pinpoint red spots on the skin
  • rash, itchy skin
  • stomach pain or tenderness
  • swelling of the feet or lower legs
  • trouble with breathing upon exertion
  • unusual bleeding or bruising
  • unusual tiredness or weakness
  • yellow eyes or skin

Less common

  • Chest pain
  • joint pain
  • sore throat
  • sores, ulcers, or white spots on the lips or in the mouth
  • swollen glands

Incidence not known

  • Anxiety
  • blurred vision
  • cold sweats
  • coma
  • confusion
  • constipation
  • depression
  • diarrhea
  • dizziness
  • fast heartbeat
  • heartburn
  • increased hunger
  • increased sensitivity of the skin to sunlight
  • indigestion
  • joint pain, stiffness, or swelling
  • nervousness
  • nightmares
  • redness or other discoloration of the skin
  • seizures
  • severe sunburn
  • shakiness
  • slurred speech
  • stomach cramping or burning
  • vomiting of blood or material that looks like coffee grounds

Other side effects of Mercaptopurine

Some side effects of mercaptopurine may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Less common

  • Darkening of the skin

Incidence not known

  • Hair loss or thinning of the hair
  • low sperm count

For Healthcare Professionals

Applies to mercaptopurine: oral suspension, oral tablet.


Very common (10% or more): Bone marrow suppression (e.g., anemia, leukopenia, thrombocytopenia) (more than 20%)[Ref]


Frequency not reported: Hyperuricemia[Ref]


Common (1% to 10%): Stomatitis, diarrhea, vomiting, nausea

Uncommon (0.1% to 1%): Pancreatitis, oral ulceration

Very rare (less than 0.01%): Intestinal ulceration[Ref]


Common (1% to 10%): Biliary stasis, hepatotoxicity

Uncommon (0.1% to 1%): Hepatic necrosis

Frequency not reported: Hepatotoxicity[Ref]


Uncommon (0.1% to 1%): Skin rash

Rare (less than 0.1%): Facial edema, alopecia

Frequency not reported: Photosensitivity reaction[Ref]


Rare (less than 0.1%): Transient oligospermia[Ref]


Frequency not reported: Fetotoxicity[Ref]


Rare (0.01% to 0.1%): Neoplasms including lymphoproliferative disorders, skin cancers (melanomas and non-melanomas), sarcomas (Kaposi's and non-Kaposi's), uterine cervical cancer in situ

Very rare (less than 0.01%): Secondary leukemia, myelodysplasia

Frequency not reported: Hepatosplenic T-cell lymphoma[Ref]


Uncommon (0.1% to 1%): Bacterial and viral infections, infections associated with neutropenia, drug fever

Frequency not reported: Immunosuppression, macrophage activation syndrome[Ref]


Common (1% to 10%): Anorexia

Frequency not reported: Hypoglycemia In patients with inflammatory bowel disease (IBD) (IBD is not an approved indication of this drug)[Ref]

Nervous system

Uncommon (0.1% to 1%): Arthralgia[Ref]


Postmarketing reports: Portal hypertension[Ref]


1. Product Information. Purixan (mercaptopurine). AnovoRx Distribution. 2019.

2. Product Information. Mercaptopurine (mercaptopurine). Mylan Pharmaceuticals Inc. 2019.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.