This study examined why some people don’t respond well to common antidepressant medications called SSRIs. Researchers used prescription records from over 38,000 people to identify those who switched to different antidepressants as a sign of poor response. They found that people with higher education and income were less likely to switch medications, and that genetic factors influenced who responded poorly to treatment. The research demonstrates that switching medications can serve as a reliable marker for identifying nonresponders, potentially helping doctors personalize antidepressant prescribing in the future.