This systematic review investigates the link between heat exposure and mental health, finding that both high temperatures and heatwaves correlate with increased mental health-related mortality and morbidity. Analyzing over 50 studies, researchers observed that with each 1°C increase, relative risk (RR) for mental health-related mortality and morbidity slightly rises, with substance-related and organic mental disorders showing the highest mortality risk. Vulnerable groups, such as those over 65 and residents of tropical or subtropical zones, face heightened risks. The review highlights the importance of further research to explore how factors like age, socioeconomic status, and climate zone influence these effects, especially as global temperatures continue to rise.