This meta-analysis evaluates the relationship between adherence to drug therapy, including placebo, and mortality. The study included 21 observational studies with 46,847 participants, focusing on the association between good and poor adherence to drug therapy. Key findings include: - Good adherence to drug therapy was associated with lower mortality (odds ratio 0.56, 95% confidence interval 0.50 to 0.63). - Good adherence to placebo was also associated with lower mortality (odds ratio 0.56, 0.43 to 0.74). - Good adherence to harmful drug therapy was associated with increased mortality (odds ratio 2.90, 1.04 to 8.11). The study concludes that good adherence to drug therapy is linked to positive health outcomes and supports the concept of the "healthy adherer" effect, where adherence to drug therapy may be a surrogate marker for overall healthy behavior. The findings highlight the importance of adhering to prescribed drug therapy for better health outcomes and suggest that stratifying patients by adherence groups can aid in identifying harmful therapies early.This meta-analysis evaluates the relationship between adherence to drug therapy, including placebo, and mortality. The study included 21 observational studies with 46,847 participants, focusing on the association between good and poor adherence to drug therapy. Key findings include: - Good adherence to drug therapy was associated with lower mortality (odds ratio 0.56, 95% confidence interval 0.50 to 0.63). - Good adherence to placebo was also associated with lower mortality (odds ratio 0.56, 0.43 to 0.74). - Good adherence to harmful drug therapy was associated with increased mortality (odds ratio 2.90, 1.04 to 8.11). The study concludes that good adherence to drug therapy is linked to positive health outcomes and supports the concept of the "healthy adherer" effect, where adherence to drug therapy may be a surrogate marker for overall healthy behavior. The findings highlight the importance of adhering to prescribed drug therapy for better health outcomes and suggest that stratifying patients by adherence groups can aid in identifying harmful therapies early.