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Table of Contents > Supplements > Cysteine
Cysteine
Also Known As:  N-acetyl-L-cysteine (NAC), L-cysteine, acetylcysteine
 
Overview
Uses
Dietary Sources
Available Forms
How to Take It
Precautions
Possible Interactions
Supporting Research

Overview

Cysteine is an amino acid that can be found in many proteins throughout the body. N-acetyl-L-cysteine (NAC), a modified form of cysteine, helps break down mucus and detoxify harmful substances in the body. Both cysteine and NAC have been shown to increase levels of the antioxidant glutathione.

Antioxidants are substances that scavenge free radicals, damaging compounds in the body that alter cell membranes, tamper with DNA, and even cause cell death. Free radicals occur naturally in the body, but environmental toxins (including ultraviolet light, radiation, cigarette smoking, and air pollution) can also increase the number of these damaging particles. Free radicals are believed to contribute to the aging process as well as the development of a number of health problems including heart disease and cancer. Antioxidants such as glutathione can neutralize free radicals and may reduce or even help prevent some of the damage they cause.


Uses

NAC offers a variety of potential therapeutic uses, particularly in the prevention or in the treatment of the following conditions:

Acetaminophen Poisoning

Healthcare practitioners commonly administer oral or intravenous NAC to prevent or reduce liver and kidney damage associated with overdoses of acetaminophen (also called paracetamol), an over the counter medication commonly used for pain or headache. Acetaminophen poisoning can occur at lower doses of the drug if someone drinks alcohol on a regular basis.

Heart Disease

In studies of people having a heart attack or those with ongoing chest pain, NAC, in combination with nitroglycerin (a drug that opens up blood vessels and improves blood flow), has been more effective than either NAC or nitroglycerin alone in reducing subsequent chest pain, heart attack, and the risk of death. However, individuals who receive both NAC and nitroglycerin may experience a severe headache. These results are promising, but further studies are needed to confirm the safety and effectiveness of NAC for heart disease.

Respiratory Illness

A review of scientific studies also found that NAC may help dissolve mucus and improve symptoms associated with chronic bronchitis, asthma, cystic fibrosis and emphysema. Chronic smokers also may benefit from NAC supplementation. Studies on large groups of people have found that NAC appears to have cancer prevention properties in people who are at risk for lung cancer.

Free radical damage is believed to contribute to the development and progression of acute respiratory distress syndrome (ARDS), a condition characterized by the rapid and progressive malfunction of the lungs. Although not all studies agree, some research of animals and people suggest that intravenous NAC may boost levels of glutathione and subsequently prevent and/or treat lung damage caused by ARDS. However, results of other studies have been conflicting. Further investigation is needed.

HIV/AIDS

HIV infection is considered to be a condition of excessive oxidative stress (caused by free radicals) where the antioxidant glutathione is depleted significantly. Therefore, it is believed that supplementation with cysteine may help strengthen the immune system in those with HIV and diminish the bodily damage associated with this infection.

In one well-designed study of people with HIV, those who took a daily supplement regimen including the amino acid glutamine (40 gram per day), vitamin C (800 mg), vitamin E (500 IU), beta-carotene (27,000 IU), selenium (280 mcg), and N-acetylcysteine (2400 mg) gained significantly more weight after 12 weeks than those who took placebo. Similarly, in a smaller-scale study using NAC in HIV positive patients, the supplement did increase glutathione levels while a placebo did not.

These studies and others support the theory that NAC may prove to be a useful addition to conventional medical care for those with HIV. Other studies, however, have shown negative results using NAC for those with HIV. Therefore, more research is needed before conclusions can be drawn about NAC supplements for this infection.

Other:

Low levels of cysteine may be linked to an increased risk of cervical dysplasia (changes to the opening of the uterus, that are precancerous or cancerous). Preliminary evidence also suggests that NAC supplements may:

  • Improve symptoms associated with Sjogren's syndrome (an autoimmune disorder characterized by dry mouth and dry eyes)
  • Enhance cognitive functioning in some individuals with Alzheimer's disease
  • Prevent development of cataracts and macular degneration
  • Slow down motor impairment in amyotrophic lateral sclerosis (ALS, often called Lou Gehrig's disease which is a progressive loss of control of voluntary muscles due to destruction of nerve cells in the brain and spinal cord)
  • Help treat hepatitis C when combined with standard medical treatment
  • Increase HDL cholesterol (the good kind of cholesterol).

Further studies are needed to confirm these early findings.


Dietary Sources

The body synthesizes cysteine from the essential amino acid methionine. Cysteine is also found in most high-protein foods including ricotta, cottage cheese, yogurt, pork, sausage meat, chicken, turkey, duck, luncheon meat, wheat germ, granola, and oat flakes.


Available Forms
  • NAC aerosol spray (prescription)
  • NAC liquid solution (prescription)
  • NAC topical solution
  • L-cysteine powder
  • Cysteine/NAC tablets or capsules

How to Take It

NAC is administered either intravenously or orally in the hospital to treat acetaminophen (paracetamol) poisoning in both children and adults. Acetaminophen poisoning is a medical emergency and treatment must be started within eight hours of an overdose.

Pediatric

There is no specific pediatric recommendation for cysteine. If laboratory tests reveal that the child has an amino acid imbalance that requires treatment, a healthcare provider may recommend a complete amino acid supplement that contains cysteine.

Adult

Recommended adult doses of NAC vary depending on the health condition being treated. The following list provides guidelines for the most common uses.

  • Respiratory illness: 200 mg two times per day for chronic bronchitis. ARDS is a medical emergency and is treated in the intensive care unit in the hospital with intravenous NAC as part of a comprehensive treatment regimen.
  • Antioxidant protection/general health: 500 mg per day to start. Dosage may be increased, with expert guidance. Someone with HIV/AIDS may be put on a dose as high as 4,000 mg per day. Adding a multivitamin will ensure that you are getting the B vitamins you need when taking NAC.

Precautions

Because of the potential for side effects and interactions with medications, dietary supplements should be taken only under the supervision of a knowledgeable healthcare provider.

Some forms of cysteine are toxic and should be avoided. These include D-cysteine, D-cystine, and 5-methyl cysteine.

NAC may raise levels of homocysteine, an amino acid believed to play a role in the development of heart disease. Be sure to have your health care provider check your homocysteine level if you are taking NAC.

Extremely high doses (more than 7 grams) of cysteine should be avoided because it may be toxic to human cells and may even lead to death.

Oral NAC may cause nausea, vomiting, and diarrhea.

Intravenous administration of NAC (to treat, for example, acetaminophen poisoning) may cause severe allergic reactions, even angioedema (significant swelling of the soft tissue just beneath the skin including the face, lips, and around the eyes) or anaphylaxis (a life-threatening allergy that leads to inability to breath). Plus, there has been one case report of seizures from intravenous administration of NAC to a young girl for paracetamol intoxication.

Cysteine supplements should not be taken by individuals with cystinuria, a kidney condition in which excessive amounts of cysteine (along with three other amino acids) are lost in the urine.


Possible Interactions

If you are currently being treated with any of the following medications, you should not use cysteine supplements without first talking to your healthcare provider.

Blood Pressure Medications, Angiotensin-converting Enzyme (ACE) Inhibitors
NAC may enhance the blood pressure-lowering effects of ACE inhibitors, medications commonly used to treat high blood pressure. Examples of ACE inhibitors include benazepril, captopril, enalapril, fosinopril, lisinopril, moexipril, quenipril, ramepril, and trandolapril.

Immunosuppressive Medications
Treatment with NAC may enhance the effectiveness of immunosuppressive medications such as azathioprine, cyclophosphamide, prednisolone, or prednisone. More research in this area is needed.

Cisplatin and Doxorubicin
Laboratory and animal studies have suggested that NAC may reduce the toxic effects associated with both cisplatin and doxorubicin, medications used to treat a variety of cancers. However, scientific studies are needed to see if these effects apply to people.

Nitroglycerin and Isosorbide
Although NAC may enhance the effectiveness of nitroglycerin and isosorbide (two medications commonly used to treat chest pain), this combination may also increase the risk of side effects such as severe headaches and may lead to abnormally low blood pressure.

Oxiconazole
Topical applications of NAC may increase the effectiveness of oxiconazole, an antifungal medication used for athlete's foot.


Supporting Research

Adair JC, Knoefel JE, Morgan N. Controlled trial of N-acetylcysteine for patients with probable Alzheimer's disease. Neurology. 2001;57(8):1515-1517.

Ames BN. Micronutrient deficiencies: A major cause of DNA damage. Ann NY Acad Sci. 2000;889:87-106.

Andreassen OA, Dedeoglu A, Klivenyi P, Beal MF, Bush AI. N-acetyl-L-cysteine improves survival and preserves motor performance in an animal model of familial amylotrophic lateral sclerosis. Neuroreport. 2000;11(11):2491-2493.

Ardissino D, Merlini PA, Savonitto S, Demicheli G, et al. Effect of transdermal nitroglycerin or N-Acetylcysteine, or both, in the long-term treatment of unstable angina pectoris. J Am Coll Cardiol. 1997;29(5):941-947.

Arstall MA, Yang J, Stafford I, Betts WH, Horowitz JD. N-acetylcysteine in combination with nitroglycerin and streptokinase for treatment of evolving acute myocardial infarction: safety and biochemical effects. Circulation. 1995;92:2855-2862.

Behr J, Maier K, Degenkolb B, Krombach F, Vogelmeier C. Antioxidative and clinical effects of high-dose N-acetylcysteine in fibrosing alveolitis. Am J Respir Crit Care Med. 1997;156:1897-1901.

Beloqui O, Prieto J, Suarez M, et al. N-acetyl cysteine enhances the response to interferon-alpha in chronic hepatitis C: a pilot study. J Interferon Res. 1993;13:279-282.

Cai J, Nelson KC, Wu M, Sternberg P Jr, Jones DP. Oxidative damage and protection of the RPE. Prog Retin Eye Res. 2000;19(2):205-221.

Carter EA. Enhanced acetaminophen toxicity associated with prior alcohol consumption in mice; prevention by N-acetylcysteine. Alcohol. Jan-Feb 1987; 4(1): 69-71.

Chevez-Barrios P, Wiseman AL, Rojas E, Ou CN, Lieberman MW. Cataract develoment in gamma-glutamyl transpeptidase deficient mice. Exp Eye Res. 2000;71(6):575-582.

Chirkov YY, Horowitz JD. N-Acetylcysteine potentiates nitroglycerin-induced reversal of platelet aggregation. J Cardiovasc Pharmacol. 1996;28(3):375-380.

Christman BW, Bernard GR. Antilipid mediator and antioxidant therapy in adult respiratory distress syndrome. New Horiz. Nov 1993; 1(4): 623-630.

D'Agostini F, Bagnasco M, Giunciuglio D, Albini A, De Flora S. Inhibition by oral N-acetylcysteine of doxorubicin-induced clastogenicity and alopecia, and prevention of primary tumors and lung micrometastases in mice. Int J Oncol. 1998;13:217-224.

Davreux CJ, Soric I, Nathens AB, et al. N-acetylcysteine attenuates acute lung injury in the rat. Shock. Dec 1997; 8(6): 432-438.

De Flora S, D'Agostini F, Masiello L, Giunciuglio D, Albini A. Synergism between N-Acetylcysteine and doxorubicin in the prevention of tumorigenicity and metastasis in murine models. Int J Cancer. 1996;67:842-848.

De Rosa SC, Zaretsky MD, Dubs JG, Roederer M, Anderson M, Green A, et al. N-acetylcysteine replenishes glutathione in HIV infection. Eur J Clin Invest. 2000;30:915-929.

Domenighetti G, Quattropani C, Schaller MD. Therapeutic use of N-acetylcysteine in acute lung diseases. [Review, French]. Rev Mal Respir. 1999;16(1):29-37.

Domenighetti G, Suter PM, Schaller MD, Ritz R, Perret C. Treatment with N-acetylcysteine during acute respiratory distress syndrome: a randomized, double-blind, placebo-controlled clinical study. J Crit Care. 1997;12(4):177-182.

Doroshow JH, Locker GY, Ifrim I, Myers CE. Prevention of doxorubicin cardiac toxicity in the mouse by N-Acetylcysteine. J Clin Invest. 1981;68:1053-1064.

Droge W. Cysteine and glutathione deficiency in AIDS patients: a rationale for the treatment with N-acetyl-cysteine. [Review]. Pharmacology. 1993;46(2):61-65.

Franceschini G, et al. Dose-related increase in HDL-cholesterol levels after N-acetylcysteine in man. Pharmacol Res. Oct-Nov 1993; 28(3): 213-218.

Goodman MT, McDuffie K, Hernandez B, Wilkens LR, Selhub J. Case-control study of plasma folate, homocysteine, vitamin B12, and cysteine as markers of cervical dysplasia. Cancer. 2000;89:376-382.

Hershkovitz E, Shorer Z, Levitas A, Tal A. Status epilepticus following intravenous N-acetylcysteine therapy. Isr J Med Sci. 1996;32(11):1102-1104.

Iversen HK. N-acetylcysteine enhances nitroglycerin-induced headache and cranial artery response. Clin Pharmacol Ther. 1992;52:125-133.

Jackson IM, et al. Efficacy and tolerability of oral acetylcysteine (Fabrol) in chronic bronchitis: a double-blind placebo controlled study. J Int Med Res. 1984; 12(3): 198-206.

Kozer E, Koren G. Management of paracetamol overdose: current controversies. [Review]. Drug Saf. 2001;24(7):503-512.

Lenz AG, Jorens PG, Meyer B, et al. Oxidatively modified proteins in bronchoalveolar lavage fluid of patients with ARDS and patients at-risk for ARDS. Eur Respir J. 1999;13(1):169-174.

Marchetti G, Lodola E, Licciardello L, Colombo A. Use of N-acetylcysteine in the management of coronary artery diseases. Cardiologia. Jul 1999; 44(7): 633-637.

Micke P, Beeh KM, Schlaak JF, Buhl R. Oral supplementation with whey proteins increases plasma glutathione levels of HIV-infected patients. Eur J Clin Invest. 2001;31(2):171-178..

Muller F, Svardal AM, Nordoy I, Berge RK, Aukrust P, Froland SS. Virological and immunological effects of antioxidant treatment in patients with HIV infection. Eur J Clin Invest. 2000;30(10):905-914.

Patrick L. Hepatitis C: epidemiology and review of complementary/alternative medicine treatments. Alt Med Rev. 1999;4(4):220-238.

Pelle E, et al. Protection against cigarette smoke-induced damage to intact transformed rabbit corneal cells by N-acetyl-L-cysteine. Cell Biol Toxicol. Aug 1998; 14(4): 253-259.

Perry HE, Shannon MW. Efficacy of oral versus intravenous N-acetylcysteine in acetaminophen ovedose:results of an open-label, clinical trial. J Pediatr. Jan 1998;132(1): 149-152.

Pizzorno JE, Murray MT. Textbook of Natural Medicine. Vol 1. 2nd ed. Edinburgh: Churchill Livingstone; 1999:296-297.

Pizzulli, L, Hagendorff A, Zirbes M, Jung W, Lüderitz B. N-Acetylcysteine attenuates nitroglycerin tolerance in patients with angina pectoris and normal left ventricular function. Am J Cardiol. 1997;79:28-33.

Ruiz FJ, et al. N-acetyl-L-cysteine potentiates depressor response to captopril and enalaprilat in SHRs. Am J Physiol. Sep 1994; 267 (3 Pt 2): R767-772.

Shabert JK, Winslow C, Lacey JM, Wilmore DW. Glutamine antioxidant supplementation increases body cell mass in AIDS patients with weight loss: a randomized, double-blind controlled trial. Nutrition. 1999;11:860-864.

Shils, ME, Olson JA, Shike M, Ross AC, eds. Modern Nutrition in Health and Disease. 9th ed. Baltimore, MD: Williams & Wilkins; 1999:543-556.

Smilkstein MJ, Knapp GL, Kulig KW, Rumack BH. Efficacy of oral N-acetylcysteine in the treatment of acetaminophen overdose. Analysis of the national multicenter study (1976 to 1985). N Engl J Med. Dec 15 1988; 319(24): 1557-1562.

Stavem K. Anaphylactic reaction to N-acetylcysteine after poisoning with paracetamol. Tidsskr Nor Laegeforen. May 30 1997; 117(14): 2038-2039.

Stey C, Steurer J, Bachmann S, Medici TC, Tramer MR. The effect of oral N-acetylcysteine in chronic bronchitis: a quantitative systematic review. Eur Respir J. 2000 Aug;16(2):253-262.

Suárez C, Del Arco C, Lahera V, Ruilope LM. N-Acetylcysteine potentiates the antihypertensive effect of angiotensin converting enzyme inhibitors [letter]. Am J Hypertens. 1995;8:859-861.

van Hoogdalem EJ, van den Hoven WE, Terpstra IJ, van Zijtveld J, Verschoor, JSC. Nail penetration of the antifungal agent oxiconazole after repeated topical application in healthy volunteers, and the effect of acetylcysteine. Eur J Pharm Sci. 1997;5:119-127.

van Zandwijk N. N-acetylcysteine for lung cancer prevention. Chest. 1995;107(5):1437-1441.

Walters MT, et al. A double-blind, cross-over, study of oral N-acetylcysteine in Sjogren's syndrome. Scand J Rheumatol Suppl. 1986; 61: 253-258.


Review Date: April 2002
Reviewed By: Participants in the review process include: Jacqueline A. Hart, MD, Department of Internal Medicine, Newton-Wellesley Hospital, Harvard University and Senior Medical Editor Integrative Medicine, Boston, MA; Gary Kracoff, RPh (Pediatric Dosing section February 2001), Johnson Drugs, Natick, Ma; Steven Ottariono, RPh (Pediatric Dosing section February 2001), Veteran's Administrative Hospital, Londonderry, NH; Margie Ullmann-Weil, MS, RD, specializing in combination of complementary and traditional nutritional therapy, Boston, MA. All interaction sections have also been reviewed by a team of experts including Joseph Lamb, MD (July 2000), The Integrative Medicine Works, Alexandria, VA;Enrico Liva, ND, RPh (August 2000), Vital Nutrients, Middletown, CT; Brian T Sanderoff, PD, BS in Pharmacy (March 2000), Clinical Assistant Professor, University of Maryland School of Pharmacy; President, Your Prescription for Health, Owings Mills, MD; Ira Zunin, MD, MPH, MBA (July 2000), President and Chairman, Hawaii State Consortium for Integrative Medicine, Honolulu, HI.

Copyright © 2004 A.D.A.M., Inc

The publisher does not accept any responsibility for the accuracy of the information or the consequences arising from the application, use, or misuse of any of the information contained herein, including any injury and/or damage to any person or property as a matter of product liability, negligence, or otherwise. No warranty, expressed or implied, is made in regard to the contents of this material. No claims or endorsements are made for any drugs or compounds currently marketed or in investigative use. This material is not intended as a guide to self-medication. The reader is advised to discuss the information provided here with a doctor, pharmacist, nurse, or other authorized healthcare practitioner and to check product information (including package inserts) regarding dosage, precautions, warnings, interactions, and contraindications before administering any drug, herb, or supplement discussed herein.

 
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HIV and AIDS
Lung Cancer
Macular Degeneration
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