Mercaptopurine: uses, dosing, side effects & brands
Mercaptopurine is a medicine sold in the U.S. under one brand, for non-hodgkin lymphoma, b-cell chronic lymphocytic leukemia and precursor cell lymphoblastic leukemia-lymphoma. Below: what the FDA label says, every product that contains it, what the pills look like, and its recall record.
Key facts
- Treats
- Non-Hodgkin Lymphoma, B-Cell Chronic Lymphocytic Leukemia and Precursor Cell Lymphoblastic Leukemia-Lymphoma
- Available as
- Tablet
- Sold as
- Purinethol
- Prescription?
- Prescription only
- Generic available?
- Not in our catalog
- What the pharmacy pays
- about $30 for a 30-count supply — not your price
How mercaptopurine is dosed
From the FDA label for Purinethol (application NDA009053). Other mercaptopurine products — different forms, different strengths — are dosed differently. Follow the label for the one you were prescribed.
The recommended starting dose of mercaptopurine tablets is 1.5 mg/kg to 2.5 mg/kg orally once daily as part of a combination chemotherapy maintenance regimen. Adjust dose to maintain desirable absolute neutrophil count and for excessive myelosuppression. (2.1) Renal Impairment : Use the lowest recommended starting dose or increase the dosing interval. (2.3, 8.6) Hepatic Impairment : Use the lowest recommended starting dose. (2.3, 8.7) 2.1 Recommended Dosage The recommended starting dosage of mercaptopurine tablets is 1.5 mg/kg to 2.5 mg/kg orally once daily as part of combination chemotherapy maintenance regimen. A recommended dosage for patients less than 17 kg is not achievable, because the only available strength is 50 mg. Take mercaptopurine tablets either consistently with or without food. After initiating mercaptopurine tablets, monitor complete blood count (CBC) and adjust the dose to maintain absolute neutrophil count (ANC) at a desirable level and for excessive myelosuppression. Evaluate the bone marrow in patients with prolonged myelosuppression or repeated episodes of myelosuppression to assess leukemia status and marrow cellularity. Evaluate thiopurine S-methyltransferase (TPMT) and nucleotide diphosphatase (NUDT15) status in patients with severe myelosuppression or repeated episodes or myelosuppression [see Dosage and Administration (2.2)] . Do not administer to…
Mercaptopurine side effects
The following clinically significant adverse reactions are described elsewhere in the labeling: Myelosuppression [see Warnings and Precautions (5.1)] Hepatotoxicity [see Warnings and Precautions (5.2)] Immunosuppression [see Warnings and Precautions (5.3)] Treatment related malignancies [see Warnings and Precautions (5.4)] Macrophage activation syndrome [see Warnings and Precautions (5.5)] The most common adverse reaction (>20%) is myelosuppression, including anemia, leukopenia and thrombocytopenia. Adverse reactions occurring in 5% to 20% of patients include anorexia, nausea, vomiting, diarrhea, malaise and rash. (6.1) To report SUSPECTED ADVERSE REACTIONS, contact Florida Pharmaceutical Products, LLC at 1-800-315-0985 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. Based on multicenter cooperative group ALL trials, the most common adverse reaction occurring in > 20% of patients was myelosuppression, including anemia, neutropenia, lymphopenia and thrombocytopenia. Adverse reactions occurring in 5% to 20% of patients included anorexia, nausea, vomiting, diarrhea, malaise and rash.…
Who shouldn’t take mercaptopurine
None. None.
Mercaptopurine drug interactions
Allopurinol : Reduce the dose of mercaptopurine tablets when co-administered with allopurinol. (2.4, 7.1) Warfarin : Mercaptopurine tablets may decrease the anticoagulant effect. (7.2) 7.1 Allopurinol Allopurinol can inhibit the first-pass oxidative metabolism of mercaptopurine by xanthine oxidase, which can lead to an increased risk of mercaptopurine adverse reactions (i.e., myelosuppression, nausea, and vomiting) [see Warnings and Precautions (5.1), Adverse Reactions (6.1)] . Reduce the dose of mercaptopurine tablets when coadministered with allopurinol [see Dosage and Administration (2.4)] . 7.2 Warfarin The concomitant administration of mercaptopurine tablets and warfarin may decrease the anticoagulant effectiveness of warfarin. Monitor the international normalized ratio (INR) in patients receiving warfarin and adjust the warfarin dosage as appropriate. 7.3 Myelosuppresive Products Mercaptopurine tablets can cause myelosuppression. Myelosuppression may be increased when mercaptopurine tablets is coadministered with other products that cause myelosuppression. Enhanced myelosuppression has been noted in some patients also receiving trimethoprim-sulfamethoxazole. Monitor the CBC and adjust the dose of mercaptopurine tablets for excessive myelosuppression [see Dosage and Administration (2.1), Warnings and Precautions (5.1)] . 7.4 Aminosalicylates Aminosalicylates (e.g., mesalamine, olsalazine or sulfasalazine) may inhibit the TPMT enzyme, which may increase the risk of myelosuppression when coadministered with mercaptopurine tablets. When aminosalicylates and mercaptopurine tablets are coadministered, use the lowest possible doses for each drug and monitor more frequently for myelosuppression [see Warnings and Precautions (5.1)] . 7.5 Hepatotoxic Products Mercaptopurine tablets can cause hepatotoxicity. Hepatotoxicity may be increased when mercaptopurine tablets is coadministered with other products that cause hepatotoxicity. Monitor liver tests more frequently in patients who are receiving mercaptopurine tablets with other hepatotoxic products [see Warnings and Precautions (5.2)] .
Every mercaptopurine product we track (1)
Same active ingredient — different manufacturer, form, price and FDA recall record. That last one is what our independent score measures.
Only one: Purinethol.
What mercaptopurine pills look like
Imprint codes, colour and shape from the FDA’s labelling data. Match the imprint on your pill — or search any imprint.
| Imprint | Strength | Colour | Shape | Maker |
|---|---|---|---|---|
| 54;420 | 50 mg | yellow | round | — |
Mercaptopurine recalls
From the FDA Enforcement database. A recall covers specific lots — not the drug as a whole.
How long mercaptopurine keeps
The date on a sealed pack is not the only one: some mercaptopurine labels start a second clock once the product is opened or mixed, as short as 8 weeks.
Does mercaptopurine expire? The in-use limits and storage rules from its labelsMercaptopurine and breastfeeding
From LactMed, the US National Library of Medicine’s Drugs and Lactation Database — quoted, not rewritten.
Full LactMed record for mercaptopurine: levels in milk, effects in breastfed infants, and the drugs it would consider insteadIn the treatment of conditions such as ulcerative colitis and Crohn's disease, most professional guidelines and other experts consider breastfeeding to be acceptable during mercaptopurine therapy.[1-9] Azathioprine is rapidly converted to mercaptopurine, so data from mothers taking azathioprine apply to mercaptopurine. No active metabolites of mercaptopurine were found in the blood of breastfed infants whose mothers were taking azathioprine and only poorly documented cases of mild, asymptomatic neutropenia and increased rates of infection have been reported occasionally. It might be desirable to monitor exclusively breastfed infants with a complete blood count with differential, and liver function tests if azathioprine is used during lactation, although some authors feel that such monitoring is unnecessary.[10]. See the Azathioprine record for details. Mothers with decreased activity of the enzyme that detoxifies mercaptopurine metabolites may transmit higher levels of drug to their infants in breastmilk. It might be desirable to monitor exclusively breastfed infants with a complete blood count with differential, and liver function tests if mercaptopurine is used during lactation, although some authors feel that monitoring is unnecessary.[11] Avoiding breastfeeding for 4 hours after a dose should markedly decrease the dose received by the infant in breastmilk.[12]
National Institute of Child Health and Human Development, record revised February 15, 2024. LactMed states its information is not a substitute for professional judgement.
What people report to the FDA about mercaptopurine
The FDA Adverse Event Reporting System (FAERS) collects reports from patients and clinicians. It holds 19,627 reports naming mercaptopurine, and the FDA flagged 87% of those reports as serious. The effects reported most often — leaving out reports about overdose, misuse or the condition being treated, which dominate the raw list for common medicines:
- febrile neutropenia2,071 reports
- pyrexia1,280 reports
- nausea832 reports
- vomiting810 reports
- diarrhoea740 reports
- abdominal pain739 reports
- neutropenia652 reports
- headache638 reports
Read these as a signal, not a rate. A report does not mean mercaptopurine caused the effect — anyone can file one, and many describe people taking several medicines for several conditions. Crucially there is no denominator: FAERS does not record how many people took the drug, so these counts cannot be turned into “X% of patients” — a bigger number often just means a more widely used or more talked-about drug. Duplicates exist, and publicity drives reporting. For what is actually established, read the FDA label section above.
Source: openFDA drug/event (FAERS), retrieved July 25, 2026.
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Frequently asked questions
What is mercaptopurine?
Purinethol (Mercaptopurine) is a medication used to treat Non-Hodgkin Lymphoma, B-Cell Chronic Lymphocytic Leukemia, Precursor Cell Lymphoblastic Leukemia-Lymphoma.
Can you take mercaptopurine with other medicines?
It depends on the medicine. We check it against the FDA labels rather than guessing: our interaction checker searches each drug's own label for the other and quotes what it says, naming the section it came from. Run mercaptopurine against whatever else you take — and remember that a label not naming a drug is not the same as that combination being safe.
What forms does mercaptopurine come in?
Across the brands we track, mercaptopurine is currently marketed as tablet, per the FDA's National Drug Code Directory. Each form is dosed differently — follow the label for the exact product you were prescribed.
Is there a generic mercaptopurine?
We do not currently list a generic-labelled mercaptopurine product. That does not always mean none exists — it means none appears under a generic name in the FDA data we track. Ask your pharmacist.
Has mercaptopurine been recalled?
The FDA's Enforcement database lists 1 recall record whose product description mentions mercaptopurine. The most recent: Mercaptopurine Tablets (Feb 9, 2024). A recall applies to specific lots, not to the drug as a whole — check the record for the affected lot numbers.
Cite this page
- APA
- pharmaranks. (2026, July 24). Mercaptopurine: uses, dosing, side effects & brands. https://pharmaranks.com/drugs/mercaptopurine
- MLA
- “Mercaptopurine: uses, dosing, side effects & brands.” pharmaranks, 24 July 2026, https://pharmaranks.com/drugs/mercaptopurine.
We summarise public FDA and NIH sources — for a clinical claim, cite the primary source we link to as well.
Sources: FDA openFDA drug label, National Drug Code Directory, and Enforcement (recall) database. This page reproduces public FDA data and is not medical advice. Dosing is set by your prescriber.
Read the full FDA label for mercaptopurine on DailyMed (NIH) ↗.