Participants enrolled in the United States/Canada ( odds ratio 3.1 , confidence intervals 2.0-5 .0 , vs. Latin America ) , taking more ( 7 + ) prescription medications ( odds ratio 1.7 , confidence intervals 1.1-2 .7 , vs. 0-2 medications ) , and scoring lower on the Stroke Specific Quality of Life scale ( odds ratio 1.3 , confidence intervals 1.1-1 .5 , per 10 points ) were more likely to withdraw or become lost to follow-up in the study vs. completing the study on assigned antiplatelet therapy .