Objective High-intensity interval training (HIIT) is a safe and feasible form of exercise. The aim of this meta-analysis was to investigate the mental health effects of HIIT, in healthy populations and those with physical illnesses, and to compare the mental health effects to non-active controls and other forms of exercise.

Design Random effects meta-analyses were undertaken for randomised controlled trials (RCTs) comparing HIIT with non-active and/or active (exercise) control conditions for the following coprimary outcomes: mental well-being, symptoms of depression, anxiety and psychological stress. Positive and negative affect, distress and sleep outcomes were summarised narratively.

Data sources Medline, PsycINFO, Embase and CENTRAL databases were searched from inception to 7 July 2020.

Eligibility criteria for selecting studies RCTs that investigated HIIT in healthy populations and/or those with physical illnesses and reported change in mental well-being, depression, anxiety, psychological stress, positive/negative affect, distress and/or sleep quality.

Results Fifty-eight RCTs were retrieved. HIIT led to moderate improvements in mental well-being (standardised mean difference (SMD): 0.418; 95% CI: 0.135 to 0.701; n=12 studies), depression severity (SMD: –0.496; 95% CI: −0.973 to −0.020; n=10) and perceived stress (SMD: −0.474; 95% CI: −0.796 to −0.152; n=4) compared with non-active controls, and small improvements in mental well-being compared with active controls (SMD:0.229; 95% CI: 0.054 to 0.403; n=12). There was a suggestion that HIIT may improve sleep and psychological distress compared with non-active controls: however, these findings were based on a small number of RCTs.

Conclusion These findings support the use of HIIT for mental health in the general population.

Level of evidence The quality of evidence was moderate-to-high according to the Grading of Recommendations Assessment, Development and Evaluation) criteria.

PROSPERO registration number CRD42020182643