I’ve been taking the antioxidant NAC to help with my asthma…but now I hear that it causes lung cancer. Is it safe to take NAC?


The health benefits of antioxidants such as N-acetylcysteine (NAC) have been so widely touted that many people think you can’t get too much. However, while research does confirm many of the health benefits, unless NAC is taken in an appropriate dose and in combination with the right supporting nutrients, it can be disruptive and devastating to health.

NAC is found naturally in the body. Research suggests that it protects against DNA damage that results from oxidative stress caused by free radicals—unstable molecules that break down cells, disrupting the cell DNA. Oxidative stress is especially a problem in the lungs, where free radicals can form from lung irritants such as smoking and air pollutants. The resulting cell damage leads to upper respiratory infections, such as chronic obstructive pulmonary disease/COPD (which includes emphysema and chronic bronchitis) and cancer.

Smokers and people with lung diseases such as asthma often take NAC because it helps thin mucus, reduces phlegm and coughing and eases expectoration. NAC is also a powerful detoxifier and is used in hospital settings to help clear the liver from acetaminophen overdose. Since NAC helps strengthen immunity, it’s also used as a preventive for colds and flu…and for general immune system support.

Lung Cancer Concerns

However, although NAC is beneficial when the body has more free radicals than it can handle, too much NAC creates another problem. That’s because NAC helps all the body’s cells stay alive longer—including old and damaged cells that are more likely to turn to cancer and that normally would be killed off by the body’s immune system, a process called senescence.

In fact, a recent study led by researchers at Hôpital Henri Mondor in France published in JCI Insight found that NAC not only can accelerate lung cancer, it can initiate the disease when there was no prior increased risk. The researchers tested NAC on two types of mice—normal aged mice and mice who were genetically altered to have stressed lungs similar to people with COPD. Half the aged mice and half the genetically stressed mice were fed NAC added to their drinking water…the rest just got the usual drinking water.

Results: Mice who got NAC had less emphysema (one of the main types of COPD)…but they were more likely to have lung cancer. Not surprisingly, the NAC-fed mice with genetically stressed lungs, making them already at higher risk for lung cancer, were at highest risk—they were 50% more likely to have lung tumors compared with genetically stressed mice who did not get NAC. Alarmingly, though, NAC-fed normal aged mice also had an increased risk compared with normal aged mice who did not get NAC—they were 10% more likely to have lung cancer.

Safer Way to Take NAC

Taking a NAC supplement in an appropriate dose and in combination with other supporting nutrients, such as vitamins A, C and E, can help you get the health benefits while making you less vulnerable to health risks. NAC is generally regarded as safe, and unsafe levels have not been determined. Research supports that typical doses—500 mg of NAC taken twice daily along with 25,000 IU of vitamin A (as beta-carotene)…2,000 mg of vitamin C (as ascorbic acid)…and 200 IU of vitamin E (as mixed tocopherols/tocotrienols), also taken twice daily—are therapeutic. However, individual dosage levels for these nutrients will depend on a patient’s age, lifestyle and history of chronic diseases. Check with a naturopathic doctor or a medical doctor with nutritional expertise before taking these supplements, especially if you are trying to treat a medical condition—good advice that applies to taking other antioxidants as well!