Overall forest plot from meta-analysis carried out in 11 studies a) assessing the relative risk of adverse events; and subgroup analysis performed on studies including b) low and c) high doses of N-acetylcysteine (NAC). Overall forest plot from meta-analysis carried out in 11 studies a) assessing the relative risk of adverse events; and subgroup analysis performed on studies including b) low and c) high doses of N-acetylcysteine (NAC). Mario Cazzola et al. Eur Respir Rev 2015;24:451-461 ©2015 by European Respiratory Society