Efficacy of laughter-inducing interventions in patients with somatic or mental health problems: A systematic review and meta-analysis of randomized-controlled trials

Background and purpose: Laughter-inducing interventions hold promise as affordable and easy to implement treatments for a range of ailments. The aim of this study was to build on meta-analytic evidence for the efficacy of such interventions in treating somatic or mental health patients. Methods: Studies eligible for the meta-analysis were identified by a comprehensive literature search in MEDLINE, CENTRAL, Web of Science, and PsycINFO and by a manual search (date of last search 22/06/2021). All randomized controlled trials comparing spontaneous laughter or simulated laughter to treatment as usual, no treatment/waitlist, or attention control groups were included. There were no language or date restrictions. Separate random-effects meta-analyses were conducted for mental health, physiological, and physical health outcomes. Hedges' g is reported as the standardized mean difference estimate. The study was registered on PROSPERO (#CRD42019139299). Results: Forty-five studies comprising 2,547 randomized participants were included. Laughter-inducing interventions showed significant positive effects on mental health (31 studies, 1,543 patients, g = 0.74, 95% CI [0.48; 1.00], I-2 = 81%), physiological (14 studies, 761 patients, g = 0.61 [0.20; 1.03], I-2 = 86%), and physical health outcomes (21 studies, 1,105 patients, g = 0.59 [0.30; 0.88], I-2 = 80%). Only one study reported adverse events, which were mild in nature. Conclusion: Laughter-inducing interventions can have beneficial effects on a variety of health-related outcomes including mental health, physical health, and physiological parameters. Future research should focus on examining differential intervention effects and mechanisms of action.