N-acetylcysteine (NAC) has received some scientific attention for its potential role in supporting the treatment and prevention of influenza, but the evidence is limited and not definitive. NAC is a precursor to glutathione, a major intracellular antioxidant, and is thought to modulate oxidative stress and inflammation, both of which are implicated in the pathogenesis of influenza and other respiratory viral infections.

The most notable clinical evidence comes from a double-blind, placebo-controlled trial conducted in Italy (De Flora et al., 1997), in which 262 elderly subjects were given NAC (600 mg twice daily) or placebo for six months during flu season. The study found that NAC supplementation significantly reduced the frequency and severity of influenza-like episodes and symptoms. Notably, while NAC did not reduce the incidence of laboratory-confirmed influenza infection, those who were infected experienced milder symptoms.

Additional mechanistic studies suggest that NAC may inhibit viral replication by reducing the availability of intracellular reactive oxygen species and modulating immune responses. Animal and in vitro studies also indicate possible antiviral and anti-inflammatory effects.

However, high-quality randomized controlled trials in humans are scarce, and major clinical guidelines do not currently recommend NAC as a standard treatment for influenza. Thus, while there is some scientific evidence supporting the use of NAC for influenza, it remains preliminary and its clinical relevance is not fully established.