Effectiveness of traditional meditation retreats: A systematic review and meta-analysis

•We conducted a meta-analysis to provide a review of traditional meditation retreats.•The meta-analysis included 21 studies enrolling 2,912 participants.•Psychological outcomes and mindfulness levels were measured in healthy populations.•We obtained Hedge's g=.49 in between group analyses, .45 in pre-post analyses..•Mindfulness levels strongly moderated clinical outcomes.