NAC (N-acetylcysteine)
A glutathione precursor with one notable flu-season trial and stronger data in chronic lung disease, which is a drug use, not a supplement claim.
Education only, not medical advice. Talk to your clinician before starting a supplement, especially if you are pregnant, take medication or have a condition.
Evidence grade: C (A strong, B good with gaps, C limited or mixed, D early)
The flu-season trial
In 262 mostly older adults, 600 mg of NAC twice daily for six months did not change rates of influenza infection by antibody testing, but fewer people developed symptomatic illness (25% vs 79% of infected participants) [1]. It is one trial from 1997 and has not been replicated at scale.
Lung disease is a drug context
A meta-analysis found NAC reduced exacerbations of chronic bronchitis and COPD, with higher doses performing better [2]. That is treatment of a disease and belongs with your clinician. As a supplement, NAC can only be described as supporting antioxidant defenses.*
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
Sources
- De Flora et al. 1997, Eur Respir J. doi.org/10.1183/09031936.97.10071535
- Cazzola et al. 2015, Eur Respir Rev. doi.org/10.1183/16000617.00002215
DOIs verified against Crossref and official pages checked on 2026-10-15.