Caffeine, the world's most consumed stimulant, is commonly used to combat fatigue, This review examined the unclear relationship between long-term caffeine consumption and subjective sleep quality, defined as satisfaction with sleep based on personal perception. Screening 6,908 studies, 10 were included. Results showed limited statistically significant associations, hindered by variability in study quality, data, and assessment methods. Influencing factors such as individual differences and study heterogeneity were identified. The review highlights the need for standardized tools and methodologies, urging future research to explore genetic, cultural, and timing factors to better understand caffeine's impact on sleep quality.