In this inaugural issue of Investigación y Avances en Psicología, we present studies that address the complexity of behavior and mental health through fundamental topics in psychology, such as neuroplasticity, mental health disorders, psychological intervention, and substance use. The first article explores, through magnetic resonance imaging and BrdU immunohistochemistry, the neuroplastic changes observed in Wistar rats resulting from sexual activity and physical exercise; this paper confirms the dynamic nature of the brain and its sensitivity to environmental experience. The second article highlights the close connection between physical and mental health by analyzing depressive and anxious symptoms, as well as substance use, in individuals living with chronic illnesses such as obesity, hypertension, diabetes mellitus, and asthma. The third article underscores the importance of making psychological care accessible to vulnerable populations. It presents the outcomes of a brief psychological intervention aimed at reducing depressive symptoms in women from rural communities, along with follow-up data obtained after the intervention. The fourth article examines the relationship between Theory of Mind and internalizing disorders—including major depression, generalized anxiety disorder, and social phobia—and invites reflection on how cognitive processes may be linked to the understanding of one’s own mental states and those of others. Finally, the fifth article reports the findings of a pilot study on the clinical conditions of individuals who identified methamphetamine as the drug with the greatest impact when seeking care at units of Centros de Integración Juvenil, A.C. The information obtained helps guide prevention proposals regarding this urgent public health issue. Taken together, the studies presented in this first issue encompass essential topics that underscore the need to integrate empirical evidence from diverse approaches.