Researchers discovered that a single dose of psilocybin can reduce opioid addiction-related behaviors in male mice by activating serotonin receptors in specific brain circuits, but this effect does not work the same way in females. The study reveals that psilocybin changes how the brain processes opioid rewards and withdrawal symptoms, suggesting psychedelics could become a new treatment approach for opioid addiction. However, important sex differences in how the brain responds mean treatments may need to be tailored differently for men and women.