In recent years, there has been an increase in the practice of chemsex, which is becoming an increasingly serious public health problem. The complex interaction between chemsex and mental health underscores the need to understand the psychological, social, and environmental factors that influence this practice. Methods: A qualitative descriptive phenomenological study was conducted in the community of Madrid, Spain to explore the depth of the chemsex phenomenon through a thematic analysis. Between April and June 2024, interviews were conducted with 15 MSM (gay, bisexual, and other men who have sex with men) who participate in these practices, using purposive and snowball sampling. Results: three main themes were identified, namely, (T1) contextualization of the practice, (T2) factors associated with chemsex, and (T3) strategies and interventions for risk and harm reduction. Conclusion: Chemsex is a phenomenon that combines sexual practices with substance use in complex social environments, presenting significant risks to physical, mental, and sexual health. It is necessary to implement public health interventions to mitigate these risks.