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What the label lists and what reports show

Thioguanine side effects

Thioguanine's FDA label lists its adverse reactions in its own words. FAERS holds 2,099 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is febrile neutropenia (486 reports).

  • No generic listed

Check it at the source: the thioguanine FDA label on DailyMed (effective January 8, 2025, Waylis Therapeutics LLC); the FDA FAERS public dashboard.

What does the label list?

From the label: adverse reactions

To report SUSPECTED ADVERSE REACTIONS, contact Waylis Therapeutics LLC Toll-Free at 1-888-514-4727 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. The most frequent adverse reaction to thioguanine is myelosuppression. The induction of complete remission of acute myelogenous leukemia usually requires combination chemotherapy in dosages which produce marrow hypoplasia. Since consolidation and maintenance of remission are also effected by multiple-drug regimens whose component agents cause myelosuppression, pancytopenia is observed in nearly all patients. Dosages and schedules must be adjusted to prevent life-threatening cytopenias whenever these adverse reactions are observed. Hyperuricemia frequently occurs in patients receiving thioguanine as a consequence of rapid cell lysis accompanying the antineoplastic effect. …

Source: FDA drug label, Waylis Therapeutics LLC, effective January 8, 2025 (SPL set 44b0c461-47fb-4106-ba11-6ed85530235c), via openFDA; the full label on DailyMed

What do FAERS reports show?

2,099 reports list thioguanine among the medicines taken, each a report of something that happened, not proof the medicine caused it; 376 are coded as a death and 972 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 21 reactions below, 5 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.

Reports received each year

The 25 most reported reactions

  • Febrile Neutropenia486
  • Haematotoxicity138
  • Neutropenia134
  • Pyrexia134
  • Off Label Use (a use or a product term, not a reaction)120
  • Thrombocytopenia (named in the label)100
  • Sepsis98
  • Vomiting (named in the label)87
  • Pancytopenia (named in the label)86
  • Febrile Bone Marrow Aplasia70
  • Platelet Count Decreased67
  • Venoocclusive Liver Disease67
  • Death (an outcome recorded in the report)61
  • Mucosal Inflammation60
  • Nausea (named in the label)58
  • Pneumonia53
  • Osteonecrosis51
  • Drug Ineffective (a use or a product term, not a reaction)50
  • Hepatotoxicity49
  • Abdominal Pain47
  • Headache46
  • Toxicity To Various Agents46
  • Anaemia (named in the label)44
  • Cough44
  • Product Use In Unapproved Indication (a use or a product term, not a reaction)44

Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms

What next?

Thioguanine: the full record
label, generics, price, shortages, recalls
Side effects hub
the most reported medicines and reactions