Abstract: Four studies, involving a total of 414 participants, met the inclusion criteria. Three studies were conducted in adult participants and one in adolescents. The average age of participants ranged from 14 to 43 years. The trials lasted between two months and 12 months. The interventions were based on Pennebaker's method. The risk of bias across most domains of the studies was generally considered to be low, however three of four studies were considered at high risk of bias due to lack of assessor blinding and one study was at high risk of bias for selective reporting. The interpretation of these studies was limited by diverse outcome measurements, measurement tools, control group techniques, and number and/or times of follow-up. A pooled result from the four studies, including a total of 146 intervention and 135 control participants, indicated uncertain effect in forced expiratory volume in one second (FEV1) % predicted between the disclosure group and the control group (mean difference (MD) 3.43%, 95% confidence interval (CI) -0.61% to 7.47%; very low-quality evidence) at ≤ three months' follow-up. Similarly, evidence from two studies indicated that written emotional disclosure found uncertain effect on forced vital capacity (FVC) (standardised mean difference (SMD) -0.02, 95% CI -0.30 to 0.26; low-quality evidence) and asthma symptoms (SMD -0.22, 95% CI -0.52 to 0.09; low-quality evidence) but may result in improved asthma control at ≤ three months' follow-up (SMD 0.29, 95% CI 0.01 to 0.58; low-quality evidence). We were unable to pool the data for other outcomes. Results from individual trials did not reveal a significant benefit of written emotional disclosure for quality of life, medication use, healthcare utilisation or psychological well-being. Evidence from one trial suggests a significant reduction in beta agonist use (MD -1.62, 95% CI -2.62 to -0.62; low-quality evidence) at ≤ three months' follow-up in the disclosure group compared with controls. The review did not address any adverse effects of emotional writing. Evidence was insufficient to show whether written emotional disclosure compared with writing about non-emotional topics had an effect on the outcomes included in this review. Evidence is insufficient to allow any conclusions as to the role of disclosure in quality of life, psychological well-being, medication use and healthcare utilisation. The evidence presented in this review is generally of low quality. Better designed studies with standardised reporting of outcome measurement instruments are required to determine the effectiveness of written emotional disclosure in the management of asthma.

Plain-language summary: Four studies, involving 414 participants, were included in this review. The trials lasted between two months and 12 months. One study was conducted in the UK, the other three in the USA. All studies compared emotional disclosure writing versus non-stressful writing. Three studies were conducted in adult participants and one in adolescents. The average age of participants ranged from 14 to 43 years. In all trials, most of the participants were female. There is no evidence to support that written emotional disclosure is helpful in improving lung function or symptoms in patients with asthma. However, disclosure may be beneficial for patients' perceptions of their own asthma control. Based on evidence obtained from the studies, we are not able to draw conclusions about the role of written emotional disclosure in quality of life, psychological well-being, asthma medication use or use of healthcare facilities for asthma-related problems. Better designed studies are necessary to determine the effects of written emotional disclosure for patients with asthma. Our interpretation of the studies was limited by variation in study settings, topics of the non-stressful writing exercise and study duration. The evidence presented in this review is generally of low quality. This summary was current to January 2014.