Deficiency Symptoms: Cysteine deficiencies identified by inherited metabolic disorders or reduced levels in body fluid have been associated with: 1) impaired antioxidant defenses; 2) decreased ability to metabolize drugs or toxic compounds; 3) depressed immune functions; 4) some psycoses; and 5) homocystinemia. Patients with rheumatoid arthritis, hypertension, and smokers have reduced levels of cysteine in fluids and tissues. Clinical trials of cysteine supplementation have shown benefits for skin disorders, hair loss, asthma, bronchitis, allergies, cystic fibrosis, chronic obstructive pulmonary disease, heavy metal toxicity, iron deficiency, diabetes & diabetic nephropathy, seizure disorders, reducing cytoxic treatment side effects, HIV infection, and alcoholism.