Synopsis

Source of validity: Scientific
Rating (out of 5): 2

L-cysteine is an amino acid with antioxidant properties, and there is some scientific rationale for its use in supporting patients undergoing chemotherapy, primarily due to its role as a precursor to glutathione, a major cellular antioxidant. Chemotherapy agents often induce oxidative stress, leading to collateral damage in healthy tissues. L-cysteine supplementation, by boosting glutathione production, may help mitigate this oxidative damage and reduce certain side effects such as mucositis or nephrotoxicity, particularly with drugs like cisplatin.

Some preclinical studies and small human trials have investigated N-acetylcysteine (NAC), a derivative of L-cysteine, for this purpose. NAC has demonstrated protective effects against chemotherapy-induced toxicity in organs such as the kidneys and liver. However, large-scale, high-quality clinical trials using L-cysteine itself (as opposed to NAC) are lacking. There is also a theoretical concern that excessive antioxidant supplementation could reduce the efficacy of chemotherapy by protecting cancer cells in addition to healthy cells.

Overall, while there is a scientific basis and some preliminary evidence for L-cysteine (or its derivatives) in reducing chemotherapy side effects, the evidence is limited and not yet robust. Clinical guidelines do not generally recommend routine use of L-cysteine for this purpose outside of research settings. Physicians should be consulted before considering such supplementation during chemotherapy.

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