While it’s not necessary, some users end up injecting sustanon every 3 days. They feel it helps them take advantage of the propionate ester and keep a more consistent release of the drug. Although the pharmaceutical reason for the four ester was to spare the user multiple shots per week, it seems bodybuilders think the best way to take this ester mix is every 3 days. However, this is not the best way to dose sustanon. The most optimal injection schedule is every 5 days. In fact, most users will inject once a week without any issues