Psychedelics have intricate effects on the brain, engaging various neurotransmitter systems and neural pathways. This chapter starts with a brief exploration of the pharmacological effects of psychedelics, focusing on the serotonin 5-HT2A receptor. Next, I will explore leading theories on the brain-level effects of psychedelics, including the cortico-striato-thalamo-cortical, the relaxed beliefs under psychedelics, and cortico-claustro-cortical models, which emphasize altered connectivity between key brain regions like the prefrontal cortex, thalamus, and claustrum. I will focus on how psychedelics disrupt conventional cognitive processes and potentially facilitate key aspects of psychedelic experiences. Furthermore, I will review recent evidence on the potential role of the midbrain periaqueductal gray in mediating the effects of psychedelics on spiritual and religious experiences. Finally, I will address the ongoing debate between integration and pluralistic views, exploring whether a single mechanism or multiple pathways account for the multifaceted effects of psychedelics. In this way, I intend to lay out a comprehensive analysis of the neuropharmacology of psychedelices.