What the label lists and what reports show
Cysteamine side effects
Cysteamine's FDA label: “The most common adverse reactions (incidence approximately 10% or greater) are sensitivity to light, redness, eye pain/irritation, headache and visual field defects.” FAERS holds 1,390 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 eye irritation (178 reports).
- No generic listed
Check it at the source: the cysteamine FDA label on DailyMed (effective April 30, 2025, Leadiant Biosciences, Inc.); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsThe most common adverse reactions (incidence approximately 10% or greater) are sensitivity to light, redness, eye pain/irritation, headache and visual field defects.
Table 3: Adverse Reactions in >10% of Patients with Nephropathic Cystinosis Naïve to Cysteamine Treatment in an Open-Label Trial
This table is printed in the PROCYSBI label published by Horizon Therapeutics USA, Inc. of June 25, 2026; the label quoted above does not print one.
| Adverse Reaction | PROCYSBI N = 17 n (%) |
|---|---|
| Vomiting | 13 (77) |
| Gastroenteritis/viral gastroenteritis | 9 (53) |
| Diarrhea | 6 (35) |
| Breath odor | 4 (24) |
| Nausea | 3 (18) |
| Electrolyte imbalance | 2 (12) |
| Headache | 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 most common adverse reactions (incidence approximately 10% or greater) are sensitivity to light, redness, eye pain/irritation, headache and visual field defects. ( 6 ) To report SUSPECTED ADVERSE REACTIONS, contact Leadiant Biosciences, Inc. at 1-888-393-4584 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. The safety data described below reflect exposure in controlled clinical trials of six months to 19 years duration in approximately 300 patients. The most frequently reported ocular adverse reactions occurring in ≥10% of patients were sensitivity to light, redness, and eye pain/irritation, headache and visual field defects.
Source: FDA drug label, Leadiant Biosciences, Inc., effective April 30, 2025 (SPL set b98ee838-ed23-42a9-93b5-72579e490fba), via openFDA; the full label on DailyMed
What do FAERS reports show?
1,390 reports list cysteamine among the medicines taken, each a report of something that happened, not proof the medicine caused it; 87 are coded as a death and 375 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, 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
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Cysteamine: 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