Cysteamine is a chemical compound that can be biosynthesized in mammals, including humans, by the degradation of coenzyme A. The intermediate pantetheine is broken down into cysteamine and pantothenic acid. It is the biosynthetic precursor to the neurotransmitter hypotaurine.It is a stable aminothiol, i.e., an organic compound containing both an amine and a thiol functional groups. Cysteamine is a white, water-soluble solid. It is often used as salts of the ammonium derivative [HSCH2CH2NH3]+ including the hydrochloride, phosphocysteamine, and bitartrate.As a medication, cysteamine, sold under the brand name Cystagon among others, is indicated to treat cystinosis. Medical uses
Cysteamine is used to treat cystinosis. It is available by mouth (capsule and extended release capsule) and in eye drops.When applied topically it can scavenge free radicals and lighten skin thats been darkened as a result of post-inflammatory hyperpigmentation, sun exposure and Melasma. Tentative evidence suggests that it may be a more effective depigmentation agent than hydroquinone, retinoids and topical corticosteroids in individuals with chronic skin discoloration. 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. Adverse effects
Topical use
The most important adverse effect related to topical use might be skin irritation. However its significantly better tolerated than alternative skin lightening treatments with similar efficacy.
Research
It was studied in in vitro and animal models for radiation protection in the 1950s, and in similar models from the 1970s onwards for sickle cell anemia, effects on growth, its ability to modulate the immune system, and as a possible inhibitor of HIV.In the 1970s it was tested in clinical trials for Paracetamol toxicity which it failed, and in clinical trials for systemic lupus erythematosus in the 1990s and early 2000s, which it also failed.Clinical trials in Huntingtons disease were begun in the 1990s and were ongoing as of 2015.As of 2013, it was in clinical trials for Parkinsons disease, malaria, radiation sickness, neurodegenerative disorders, neuropsychiatric disorders, and cancer treatment.It has been studied in clinical trials for pediatric nonalcoholic fatty liver disease

References
External links
"Cysteamine". Drug Information Portal. U.S. National Library of Medicine. "Cysteamine hydrochloride". Drug Information Portal. U.S. National Library of Medicine.