L-Acetyl n-Cysteine (commonly referred to as N-acetylcysteine or NAC) is scientifically studied as a supportive treatment for Chronic Obstructive Pulmonary Disease (COPD). NAC is a precursor to the antioxidant glutathione and also has mucolytic properties, meaning it helps to thin and loosen mucus in the airways. This can be beneficial in COPD, a condition characterized by chronic inflammation and mucus production leading to obstructed airflow.

Several clinical studies and meta-analyses have evaluated the efficacy of NAC in COPD. Evidence shows that chronic oral administration of NAC (usually at doses of 600-1200 mg/day) can reduce the frequency and duration of COPD exacerbations, particularly in patients who are not receiving inhaled corticosteroids. The largest and most cited trials, such as the BRONCUS study, showed a modest reduction in exacerbation rates, although effects on lung function (FEV1) and quality of life were less pronounced. A 2015 Cochrane review concluded that NAC may reduce the risk of exacerbations, especially in patients with frequent exacerbations.

However, the overall quality of evidence is moderate, and some studies have not shown significant benefit. Guidelines from the Global Initiative for Chronic Obstructive Lung Disease (GOLD) mention NAC as a possible adjunct for select patients. In summary, scientific evidence supports a modest benefit in reducing exacerbations in COPD, but routine use is not universally recommended.