How much does laughter therapy actually reduce stress?
The evidence shows a moderate to large effect. A meta-analysis of 9 studies involving 347 participants found that laughter therapy significantly reduced stress levels, with the most effective programs using 15 steps [4]. Another meta-analysis of 48 studies reported an overall effect size of 0.668 — meaning the average person in a laughter therapy group had lower stress than about 75% of people in a control group [3]. In practical terms, a randomized trial in married immigrant women found that two weeks of laughter therapy (twice weekly) significantly lowered acculturative stress, anxiety, and depression, and also reduced salivary cortisol — a key stress hormone [5]. A study in elderly people showed a similar drop: stress scores fell significantly after laughter therapy, with a p-value of 0.000 (meaning the result is highly unlikely to be due to chance) [8].
Does it help with anxiety and depression too?
The results are mixed but promising for depression. In a randomized trial of nursing students during the pandemic, online laughter therapy significantly reduced depression scores compared to a control group, but it did not significantly lower anxiety or stress [1]. However, a study of mothers during the pandemic found that both a laughter therapy group and a control group (who watched an entertainment show) experienced decreased depression and anxiety — but only the laughter therapy group showed a significant reduction in parental stress [6]. A systematic review of 16 randomized trials concluded that laughter therapy is effective for reducing depression, stress, and anxiety, and also improves sleep quality [7]. So while the evidence for anxiety is less consistent, laughter therapy appears to have a reliable effect on depression and stress.
What about immune function — does laughter therapy boost it?
The evidence here is thin and inconclusive. One randomized trial measured salivary IgA (an antibody that helps fight infections) in immigrant women after laughter therapy and found no statistically significant change compared to the control group [5]. A systematic review noted that there was only limited evidence for effects on blood glucose, blood pressure, endorphins, and cortisol levels [7]. While some studies suggest laughter may increase endorphins and improve overall well-being [2], the direct link to immune function remains unproven. In short, laughter therapy is a solid stress-reduction tool, but claims about boosting immunity are not yet backed by strong evidence.
Sources used in this answer
The effect of online laughter therapy on depression, anxiety, stress, and loneliness among nursing students during the Covid-19 pandemic
Online laughter therapy significantly reduced depression in nursing students but did not significantly affect anxiety, stress, or loneliness.
Effect of Laughter Therapy on the Psychological and Physiological State of a Person
Survey data showed laughter therapy improved mood (24%), reduced stress and improved well-being (34%), and increased energy and optimism (22%).
Is Laughter Therapy Useful in a Health CRISIS?: Meta-Analysis of Laughter Therapy
Meta-analysis of 48 studies found an overall effect size of 0.668 for laughter therapy, with strongest effects on social and psycho-somatic outcomes.
Effectiveness of Laughter Therapy for Managing Stress: A Meta-Analysis
Meta-analysis of 9 studies (347 participants) found laughter therapy significantly reduced stress, with 15-step programs being most effective.
Effects of laughter therapy on the stress response of married immigrant women in South Korea: A randomized controlled trial
Randomized trial in immigrant women showed laughter therapy significantly decreased acculturative stress, anxiety, depression, and salivary cortisol, but not salivary IgA.
A pilot randomized controlled trial of distance laughter therapy for mothers' level of depression, anxiety, and parental stress during the COVID-19 pandemic.
Pilot trial in mothers during COVID-19 found both laughter therapy and a control TV show reduced depression and anxiety, but only laughter therapy reduced parental stress.
The Effect of Laughter Therapy on Physical and Mental Health: Systematic Review
Systematic review of 16 RCTs concluded laughter therapy reduces pain, depression, stress, and anxiety, and improves sleep quality, but evidence for immune markers was limited.
Effect Of Laughter Therapy On Stress In The Eldery
Quasi-experimental study in elderly people found a significant reduction in stress scores after laughter therapy (p = 0.000).