What the label lists and what reports show
Tiopronin side effects
Tiopronin's FDA label: “Most common adverse reactions (≥10%) are nausea, diarrhea or soft stools, oral ulcers, rash, fatigue, fever, arthralgia, proteinuria, and emesis.” FAERS holds 2,449 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 nausea (194 reports).
- Generic listed
Check it at the source: the tiopronin FDA label on DailyMed (effective October 7, 2025, Mission Pharmacal Company); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsMost common adverse reactions (≥10%) are nausea, diarrhea or soft stools, oral ulcers, rash, fatigue, fever, arthralgia, proteinuria, and emesis.
A table the label prints in its adverse reactions section without a title; its column headings name the groups compared
| Adverse Reaction | Table 1: Group 1 Previously treated with d‑penicillamine (N = 49) | Adverse Reactions Occurring in One or More Patients Group 2 Naïve to d‑penicillamine (N = 17) |
|---|---|---|
| anemia | 1 (2%) | 1 (6%) |
| nausea | 12 (25%) | 2 (12%) |
| fever | 4 (8%) | – |
| anorexia | 4 (8%) | – |
| proteinuria | 5 (10%) | 1 (6%) |
| rash | 7 (14%) | 2 (12%) |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
From the label: adverse reactions, continuedThe following adverse reactions are discussed in greater detail in other sections of the labeling: Proteinuria [see Warnings and Precautions ( 5.1 )] Hypersensitivity [see Warnings and Precautions ( 5.2 )] Most common adverse reactions (≥10%) are nausea, diarrhea or soft stools, oral ulcers, rash, fatigue, fever, arthralgia, proteinuria, and emesis. ( 6 ) To report SUSPECTED ADVERSE REACTIONS, contact Mission Pharmacal Company at toll-free phone # 1-800-298-1087 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, the adverse reaction rates observed in the clinical trials of the drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. Adverse reactions occurring at an incidence of ≥5% in an uncontrolled trial in 66 patients with cystinuria age 9 to 68 years are shown in the table below. Patients in group 1 had previously been treated with d-penicillamine; those in group 2 had not. Of those patients who had stopped taking d-penicillamine due to toxicity (34 out of 49 patients in group 1), 22 were able to continue treatment with THIOLA. In those without prior history of d-penicillamine treatment, 6% developed reactions of sufficient severity to require THIOLA withdrawal. …
Source: FDA drug label, Mission Pharmacal Company, effective October 7, 2025 (SPL set 20298a52-a194-a161-8632-d84b6f26e23c), via openFDA; the full label on DailyMed
What do FAERS reports show?
2,449 reports list tiopronin among the medicines taken, each a report of something that happened, not proof the medicine caused it; 88 are coded as a death and 308 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 22 reactions below, 18 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?
- Tiopronin: 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