55 trials with 3 121 patients were included in a Cochrane review . 37 trials assessed physical methods, 10 assessed chemical methods, and 8 a combination of chemical and physical methods. For the most frequently reported outcome, peak flow in the morning (1 665 patients), the SMD was –0.01 (95% CI –0.08 to 0.11). There were no statistically significant differences either in number of patients improved (RR 1.01, 95% CI 0.80 to 1.27), asthma symptom scores (SMD –0.06, 95% CI –0.16 to 0.05), or in medication usage (SMD -0.05, 95% CI –0.17 to 0.07).
Comment: The quality of evidence is downgraded by study limitations (unclear allocation concealment).