In the absence of a systematic review, we often go looking for randomised controlled trials as the best available evidence to answer questions about treatment.
These two small randomised controlled trials from Korea and Iran respectively, investigate the effectiveness of laughter on mental health.
The first trial from Kyungpook National University Hospital investigated the effects of laughter therapy on depression, cognitive function, quality of life, and the sleep patterns of elderly people living in the community. Patients were randomised to either a control group or laughter therapy and compared using various outcome measures (Geriatric Depression Scale, Mini-Mental State Examination, Short-Form Health Survey-36, Insomnia Severity Index and Pittsburgh Sleep Quality Index).
The laughter therapy showed small positive effects on depression, insomnia, and sleep quality, but the number of patients in the trial and the length of the study make these findings fairly weak.
Ko HJ, Youn CH. Effects of laughter therapy on depression, cognition and sleep among the community-dwelling elderly. Geriatr Gerontol Int. 2011 Jul;11(3):267-74. doi: 10.1111/j.1447-0594.2010.00680.x. Epub 2011 Jan 17. [PubMed abstract]
The second trial involved 60 depressed elderly female patients who were members of a cultural community in Tehran. These women were randomised to a control group, exercise therapy or laughter yoga, which is described as a combination of unconditioned laughter and yogic breathing.
The authors conclude that:
Laughter Yoga is at least as effective as group exercise program in improvement of depression and life satisfaction of elderly depressed women.
Again, this is a small trial and the findings should be interpreted with that in mind.
Shahidi M, Mojtahed A, Modabbernia A, Mojtahed M, Shafiabady A, Delavar A, Honari H. Laughter yoga versus group exercise program in elderly depressed women: a randomized controlled trial. Int J Geriatr Psychiatry. 2011 Mar;26(3):322-7. doi: 10.1002/gps.2545. Epub 2010 Sep 16. [PubMed abstract]