Forest plot from meta-analysis carried out on four studies including high-dose N-acetylcysteine (NAC) treatment a) assessing the relative risk of chronic obstructive pulmonary disease (COPD) exacerbations and b) subgroup analysis performed on two randomised... Forest plot from meta-analysis carried out on four studies including high-dose N-acetylcysteine (NAC) treatment a) assessing the relative risk of chronic obstructive pulmonary disease (COPD) exacerbations and b) subgroup analysis performed on two randomised clinical trials in which inclusion criteria required diagnosis of COPD by pulmonary function testing. Mario Cazzola et al. Eur Respir Rev 2015;24:451-461 ©2015 by European Respiratory Society