Ref (type)	Population	Outcome, Interventions	Results and statistical analysis	Effect size	Favours
COPD exacerbations
[72] Systematic review	5055 people 23 RCTs in this analysis	Average number of exacerbations 2 to 36 months with mucolytics with placebo Absolute results not reported	WMD –0.05 exacerbations/month 95% CI –0.05 exacerbations/month to –0.04 exacerbations/month The results of the review should be interpreted with caution It was unclear how many people included in the review had COPD, and there was significant heterogeneity among the RCTs (symptom scores could not be pooled)	Effect size not calculated	mucolytics
[73] Systematic review	Number of people not reported 9 RCTs in this analysis	Average number of exacerbations 3 to 24 months with N-acetylcysteine with placebo Absolute results not reported	Overall weighted effect size 1.37 95% CI 1.25 to 1.50 Reduction 235 The result of the review should be interpreted with caution It was unclear how many people included in the review had COPD, and there was significant heterogeneity among the RCTs (symptom scores could not be pooled)	Effect size not calculated	N-acetylcysteine
[74] RCT	709 Chinese people with COPD, with at least 2 exacerbations per year over 2 years	Exacerbation risk 12 months 325 exacerbations in 354 people with carbocisteine 250 mg twice daily 439 exacerbations in 355 people with placebo	RR 0.75 95% CI 0.63 to 0.91 P = 0.04	Small effect size	carbocisteine