What the label lists and what reports show
Allopurinol side effects
Allopurinol's FDA label: “Most Common Adverse Reactions (≥ 1%) Gastrointestinal: Diarrhea, nausea, alkaline phosphatase increase, AST/ALT increase.” FAERS holds 155,998 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 diarrhoea (8,723 reports).
- Generic listed
- A presentation discontinued
Check it at the source: the allopurinol FDA label on DailyMed (effective May 21, 2026, Rising Pharma Holdings, Inc.); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsMost Common Adverse Reactions (≥ 1%) Gastrointestinal: Diarrhea, nausea, alkaline phosphatase increase, AST/ALT increase.
From the label: adverse reactions, continuedThe following clinically significant adverse reactions are described elsewhere in the labeling: Skin Rash and Hypersensitivity [ see Warnings and Precautions (5.1) ] Nephrotoxicity [ see Warnings and Precautions (5.3) ] Hepatoxicity [ see Warnings and Precautions (5.4) ] Myelosuppression [ see Warnings and Precautions (5.5) ] Potential Effect on Driving and Use of Machinery [ see Warnings and Precautions (5.6) ] The following adverse reactions associated with the use of allopurinol were identified in literature, unpublished clinical trials or postmarketing reports. Because some of these reactions were reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. The most frequent adverse reaction to allopurinol is skin rash. Most Common Adverse Reactions (≥ 1%) Gastrointestinal: Diarrhea, nausea, alkaline phosphatase increase, AST/ALT increase. Metabolic and Nutritional: Acute attacks of gout. Skin and Appendages: Rash, maculopapular rash. Less Common Adverse Reactions (< 1%) Body As a Whole: Ecchymosis, fever, headache, malaise. Cardiovascular: Necrotizing angiitis, vasculitis, pericarditis, peripheral vascular disease, thrombophlebitis, bradycardia, vasodilation.
Source: FDA drug label, Rising Pharma Holdings, Inc., effective May 21, 2026 (SPL set 30ad5ba2-1cef-4933-b104-0597f6a2aaa2), via openFDA; the full label on DailyMed
What do FAERS reports show?
155,998 reports list allopurinol among the medicines taken, each a report of something that happened, not proof the medicine caused it; 21,961 are coded as a death and 76,437 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, 13 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
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Allopurinol: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions