[14][13] As a medication, cysteamine, sold under the brand name Cystagon among others, is indicated to treat cystinosis, a lysosomal storage disease characterized by the abnormal accumulation of cystine, the oxidized dimer of the amino acid cysteine.

[16][8][9][6][10][7][11][17] When applied topically it can lighten skin that's been darkened as a result of post-inflammatory hyperpigmentation, sun exposure and melasma.

[18][19][20][21] Tentative evidence suggests that it may be a more effective depigmentation agent than hydroquinone, retinoids and topical corticosteroids in individuals with chronic skin discoloration.

[22][23][24] Topical application of cysteamine cream has also demonstrated similar efficacy to intradermal tranexamic acid injections for the treatment of Melasma but with much fewer adverse effects.

[24][25] The label for oral formulations of cysteamine carry warnings about symptoms similar to Ehlers-Danlos syndrome, severe skin rashes, ulcers or bleeding in the stomach and intestines, central nervous symptoms including seizures, lethargy, somnolence, depression, and encephalopathy, low white blood cell levels, elevated alkaline phosphatase, and idiopathic intracranial hypertension that can cause headache, tinnitus, dizziness, nausea, double or blurry vision, loss of vision, and pain behind the eye or pain with eye movement.

[8] Additional adverse effects of oral cysteamine include bad breath, skin odor, vomiting, nausea, stomach pain, diarrhea, and loss of appetite.