A systematic review including 11 studies with a total of 2 540 subjects was abstracted in DARE. In 9 trials, 351 of 723 participants (48.5%) receiving NAC had no exacerbation, compared with 229 of 733 participants (31.2%) receiving placebo. The relative benefit was 1.56 (95% CI: 1.37 to 1.77) and the NNT 5.8 (95% CI: 4.5 to 8.1).
In 5 trials, 286 of 466 participants (61.4%) receiving NAC reported improvement of their symptoms, compared with 160 of 462 participants (34.6%) receiving placebo. The relative benefit was 1.78 (95% CI: 1.54 to 2.05) and the NNT 3.7 (95% CI: 3.0 to 4.9).
The adverse effects were similar with NAC and placebo.