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Cystagon Side Effects

Generic name: cysteamine

Medically reviewed by Last updated on Aug 5, 2023.

Note: This document contains side effect information about cysteamine. Some dosage forms listed on this page may not apply to the brand name Cystagon.

Applies to cysteamine: oral capsule, oral capsule delayed release, oral packet.

Serious side effects of Cystagon

Along with its needed effects, cysteamine (the active ingredient contained in Cystagon) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking cysteamine:

More common

Less common


Incidence not known

Other side effects of Cystagon

Some side effects of cysteamine may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Less common

For Healthcare Professionals

Applies to cysteamine: oral capsule, oral delayed release capsule, oral granule enteric coated.


The most common adverse events were vomiting, abdominal pain, nausea, anorexia, fever, diarrhea, lethargy, headache, and rash.[Ref]


Very common (10% or more): Vomiting (35%), diarrhea (16%)

Common (1% to 10%): Nausea, bad breath, abdominal pain, dyspepsia

Uncommon (0.1% to 1%): Gastrointestinal ulceration and bleeding, constipation, gastroenteritis, duodenitis[Ref]


Very common (10% or more): Anorexia (31%)

Uncommon (0.1% to 1%): Dehydration[Ref]

Nervous system

Very common (10% or more): Lethargy (11%)

Common (1% to 10%): Dizziness, headache, encephalopathy

Uncommon (0.1% to 1%): Somnolence, seizures, convulsions, ataxia, confusion, tremor, hyperkinesia, jitteriness

Postmarketing reports: Benign intracranial hypertension with papilledema[Ref]


Very common (10% or more): Fever (22%)

Common (1% to 10%): Fatigue, asthenia

Uncommon (0.1% to 1%): Decreasing hearing[Ref]


Common (1% to 10%): Rash, skin odor

Uncommon (0.1% to 1%): Hair color changes, skin fragility (molluscoid pseudomotor on elbows)

Frequency not reported: Urticaria

Postmarketing reports: Skin lesions, skin striae, skin fragility[Ref]

Cases of Ehlers-Danlos like syndrome and vascular disorders on elbows have been reported in children chronically treated with high doses of different cysteamine preparations. In cases where histopathological examination of the skin was performed, the results suggested angioendotheliomatosis.[Ref]


Common (1% to 10%): Abnormal liver function

Frequency not reported: Elevated alkaline phosphatase[Ref]


Uncommon (0.1% to 1%): Hypertension[Ref]


Uncommon (0.1% to 1%): Abnormal urine odor[Ref]


Uncommon (0.1% to 1%): Leukopenia, anemia[Ref]


Uncommon (0.1% to 1%): Anaphylactic reaction[Ref]


Uncommon (0.1% to 1%): Joint hyperextension, leg pain, genu valgum, osteopenia, compression fracture, scoliosis

Postmarketing reports: Molluscoid pseudotumors[Ref]


Uncommon (0.1% to 1%): Nervousness, abnormal thinking, depression, emotional lability, hallucinations, nightmares[Ref]


Uncommon (0.1% to 1%): Nephrotic syndrome, interstitial nephritis, renal failure[Ref]

Cases of nephrotic syndrome have been reported within 6 months of starting therapy with progressive recovery after treatment discontinuation. In some cases, histology showed a membranous glomerulonephritis of the renal allograft and hypersensitivity interstitial nephritis.[Ref]


1. (2001) "Product Information. Cystagon (cysteamine)." Mylan Pharmaceuticals Inc

2. Cerner Multum, Inc. "UK Summary of Product Characteristics."

3. Cerner Multum, Inc. "Australian Product Information."

4. (2013) "Product Information. Procysbi (cysteamine)." Raptor Pharmaceutical Corporation

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.