A meta-analysis of the association between adherence to drug therapy and mortality was conducted, involving 21 studies with 46,847 participants. The study found that good adherence to drug therapy was associated with lower mortality compared to poor adherence, with an odds ratio of 0.56 (95% confidence interval 0.50 to 0.63). Good adherence to placebo was also associated with lower mortality (0.56, 0.43 to 0.74), and good adherence to beneficial drug therapy was associated with lower mortality (0.55, 0.49 to 0.62). Conversely, good adherence to harmful drug therapy was associated with increased mortality (2.90, 1.04 to 8.11). The study supports the existence of the "healthy adherer" effect, where adherence to drug therapy may be a surrogate marker for overall healthy behavior. The findings suggest that good adherence to drug therapy is associated with positive health outcomes. The study also highlights the importance of measuring adherence to drug therapy in clinical trials to better understand its impact on health outcomes. The study has limitations, including potential biases from unmeasured confounding variables and the use of indirect methods to measure adherence. Despite these limitations, the study provides evidence that good adherence to drug therapy is associated with lower mortality and supports the concept of the "healthy adherer" effect. The study also emphasizes the need for future research to address the causal relationship between adherence and health outcomes.A meta-analysis of the association between adherence to drug therapy and mortality was conducted, involving 21 studies with 46,847 participants. The study found that good adherence to drug therapy was associated with lower mortality compared to poor adherence, with an odds ratio of 0.56 (95% confidence interval 0.50 to 0.63). Good adherence to placebo was also associated with lower mortality (0.56, 0.43 to 0.74), and good adherence to beneficial drug therapy was associated with lower mortality (0.55, 0.49 to 0.62). Conversely, good adherence to harmful drug therapy was associated with increased mortality (2.90, 1.04 to 8.11). The study supports the existence of the "healthy adherer" effect, where adherence to drug therapy may be a surrogate marker for overall healthy behavior. The findings suggest that good adherence to drug therapy is associated with positive health outcomes. The study also highlights the importance of measuring adherence to drug therapy in clinical trials to better understand its impact on health outcomes. The study has limitations, including potential biases from unmeasured confounding variables and the use of indirect methods to measure adherence. Despite these limitations, the study provides evidence that good adherence to drug therapy is associated with lower mortality and supports the concept of the "healthy adherer" effect. The study also emphasizes the need for future research to address the causal relationship between adherence and health outcomes.